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ADVANCE KNOWLEDGE EFFECTS ON HAND MOVEMENTS AND POSTURAL ADJUSTMENTS IN CATCHING

PIETER TIJTGAT

2012

ADVANCE KNOWLEDGE EFFECTS ON HAND MOVEMENTS AND POSTURAL ADJUSTMENTS

IN CATCHING

Pieter TIJTGAT

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Supervisor: Prof. Dr. Matthieu Lenoir University Ghent

Supervisory board: Prof. Dr. Matthieu Lenoir University Ghent Prof. Dr. Simon Bennett Liverpool John Moores University Prof. Dr. Geert Savelsbergh VU University Amsterdam Manchester Metropolitan University Prof. Dr. Dirk De Clercq University Ghent

Examination board: Prof. Dr. Ilse De Bourdeaudhuij University Ghent Prof. Dr. Rob Gray University of Birmingham Prof. Dr. John van der Kamp VU University Amsterdam University of Hong Kong Prof. Dr. Ann Cools University Ghent Prof. Dr. Roel Vaeyens University Ghent Prof. Dr. Leen Haerens University Ghent

Printed by University Press, ZelzateIllustrations by Evelien JonckheereLay-out by Bert Jonckheere

© 2012 Department of Movement and Sports Sciences, Watersportlaan 2, 9000 Ghent, Belgium

ISBN …

All rights reserved. No part of this book may be reproduced, or published, in any form or in any way, by print, photo print, !"#$%&'!()%$)*+,)%-./$)!/*+0)1"-.%2-)3$"%$)3/$!"00"%+)4$%!)-./)*2-.%$5

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TABLE OF CONTENTS

ACKNOWLEDGMENTS - DANKWOORD 8

PROLOGUE 14

PART 1: GENERAL INTRODUCTION 16

>M& E,#N"8,+#+&58*5"%,3&8$&8&*00.&*0&$*'+7&"')8,&)0*01&(#"8K%0'1& & & >O

<M& @+8J*8*%0,$&*0&50,$*18%,*$&%,&58*5"%,3& & & & & & & <P

PM& G,-01)8*%0,&-01&58*5"%,3& & & & & & & & & <Q

3.1. Optical variables for catching 28

3.2. Non-visual information sources 32

RM& @+K8,5#&S,0T.#+3#&#--#5*$&& & & & & & & & PR

4.1. Advance knowledge effects for self-paced actions: wide-spread evidence 35

4.2. Advance knowledge effects for catching: preliminary indications 37

UM& 60$*'18.&8+V'$*)#,*$& & & & & & & & & PO

5.1. Postural adjustments when raising the arm 39

5.2. Advance knowledge effects on postural adjustments 41

WM& E'*.%,#&0-&*"#&*"#$%$& & & & & & & & & R<

PART 2: ORIGINAL RESEARCH 62

I!B4D&>X&&& @+K8,5#&S,0T#.+3#&#--#5*$&0,&S%,#)8*%5$&%,&0,#N"8,+#+&58*5"%,3& & WR

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& & 0-&055.'$%0,&0,&%,*#15#J*%K#&85*%0,$& & & & & & O<

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& & $*8(%.%[8*%0,&8,+&#2'%.%(1%')&50,*10.& & & & & & >><

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& & )0K#)#,*$&8,+&J0$*'18.&8+V'$*)#,*$&-01&58*5"%,3& & & & >PW

PART 3: GENERAL DISCUSSION 154

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PM& !"#01#*%58.&J#1$J#5*%K#& & & & & & & & & >W>

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WM& 6185*%58.&1#.#K8,5#&8,+&-'*'1#&+%1#5*%0,$& & & & & & & >\W

6.1. Future experimental designs: a plea for situation-dependent research 176

6.2. Daily life and sports context 178

SUMMARY - SAMENVATTING 192

EPILOGUE 200

LIST OF PUBLICATIONS 202

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3#"0.J#,M&48)#$&#,&"#1#,X&)%V,&T001+&K8,&+8,Sa&&

Professor Lenoir, Matthieu. Ruim acht jaar geleden klopte ik op je deur, zoekend naar het geschikte

scriptieonderwerp. Ik was immers gebeten door de vraag ‘hoe leer je iemand het best een motorische

vaardigheid aan?’. Je liet me binnen en zou dat de afgelopen jaren nog vele malen doen, steeds bereid

de korte vragen die ik op je afvuurde te beantwoorden. Je opende ook, rechtstreeks of onrechtstreeks,

vele andere deuren: die van het groene en andere labo’s voor experimenten met balvangers, de

practicalokalen, af en toe eens een zwembad, internationale congreszalen en onderzoekscentra in

Amsterdam en Liverpool. Jouw steun bij al deze ondernemingen en je rust in combinatie met hier en

daar plotse improvisatieopdrachten werden ten zeerste geapprecieerd. Merci!

Naast Prof. Lenoir hielden enkele andere gerenommeerde bewegingswetenschappers mij stevig in

het onderzoeksgareel. Deze thesis werd begeleid door professoren Simon Bennett, Geert Savelsbergh

en Dirk De Clercq. Uiteindelijk viel ook Jos Vanrenterghem in en hield mijn meest recente werk

wonderwel in evenwicht.

I have to come up with a very warm thanks for what Simon did for my work. I have to admit, Simon,

,%2$)'/6/+7*$,)$/7)3/+)$/32-*-"%+)*+7),%2$)#$"-"#*')*33$%*#.)./'3/7)-%)"!3$%8/)!,)1%$9)0"6+"&#*+-',5)

I would like to end this word of thanks to you by giving a citation from Liverpudlian Malcolm, who

expressed clearly his and your working style: “I think Simon and I have a same approach towards the

science that we practice, having an attitude of being strictly… but fair!”

Geert, je gaf me niet enkel de kans mijn onderzoeks- en ander geluk eventjes te gaan beproeven in

Amsterdam, je warme persoonlijkheid en gezelligheid samen met een vrije onderzoeksstijl wierp ook

hier in Gent nog eens zijn vruchten af.

Dirk, vakgroepvoorzitter, begeleider, co-auteur en raadgever wanneer ik af en toe eens met een vraag

**+):/)7/2$)9'%3-/5);/-)!**9-)!/)&/$)0%!0)%%9)</'4)//+0)!/-)//+)*+-1%%$7)%3)7/)3$%33/+)-/)92++/+)

10

komen op een vraag die jij me stelde. Ten slotte zeer lovenswaardig: je gaat er telkens voor, ook als een

jong veulen op HILO-weekend je de doorgang belemmert en zelfs uit evenwicht brengt…

Over evenwicht gesproken, Jos, laat dat nu net je specialiteit zijn. Het feit dat ik telkens aan je mouw

kon trekken bij je UGent-trips hebben me geen windeieren gelegd. Je gedrevenheid voor onderzoek

is ongeëvenaard en je diende deze voluit aan te spreken om, in combinatie met je pedagogische

kwaliteiten, mij als koppige student te overtuigen van deze of gene wetenschappelijke approach bij mijn

verblijf - op jouw uitnodiging - in Liverpool. Je was zelfs zo overtuigend dat ik je maar wat graag liet

opdraven om ook mijn collega’s te onderrichten in research skills, een wat mij betreft zeer geslaagde

samenwerking.

48,S&8..#,_&K001&V'..%#&3'..#&$*#',&#,&%S&"00J&+8*&%S&00S&%#*$&"#(&S',,#,&*#1'3+0#,&K001&V'..%#M&&

I would also like to thank the members of the examination board: Prof. Gray, Prof. van der Kamp, Prof.

Cools, Prof. Haerens, Prof. De Bourdeaudhuij and Prof. Vaeyens. I considered it as a great honour that all of

,%2)'"9/7)-%)$/*7)!,)1%$9)*+7)#%!/)%8/$)-%)=./+-)-%)>2/0-"%+)!/)%+)!,)1%$95)?%2$)#$"-"#*')$/@/#-"%+0)

*0)03/#"*'"0-0)"+)8*$"%20)0#"/+-"&#)&/'70)#/$-*"+',)"!3$%8/7)-./)1%$95

Ik wil jullie graag iets vertellen over het 2 verdiep van het HILO. Er wordt daar immers gigantisch

talent gekweekt. Met eerst Jorge, en iets later Eva en uiteindelijk ook Ilse op het bureau, leerde ik stuk voor

stuk - elk op hun manier en helemaal niet saai :-) - gedreven onderzoeksmensen kennen. Talloze collega’s

vullen deze reeks aan en ik vernoem willekeurig hen die het waarschijnlijk leuk, misschien belangrijk

vinden, maar het zeker ook verdienen in dit dankwoord vermeld te worden: Kristof, Jan, Karlijn, Pieter,

Ine, Sam, Bas, !"#$, Pieter, Joeri, Davy, Pierre, Katrien, Sanne, Inge, Audrey, Andries, Johan, Philippe, Jotie, Bert,

Katrien, Veerle, Lennert, Roel, Frederik, Jan, Wim, Isabel, Dirk, Filip, Veerle, Vera, Femke, Maité, Anne, %$&#$',

Tine, Matthieu, to name but a few… Het waren leuke babbels, doctoraatsverdedigingen, outdoorstages,

7//'!%!/+-/+)8*+) 4$20-$*-"/();ABCD1//9/+7/+()%+-E%/</!"+6/+()&'%0%4//$0/00"/0() 03%$-!%!/+-:/0()

traktaties, kortom… bedankt voor alle mooie collega-momenten!

11

De boog kan niet altijd gespannen staan, en dus kan en zal ik niet nalaten de vrienden te bedanken

die mij omringden bij deze ontspanningsmomenten. Het zijn de kompanen van talloze sportieve en

extrasportieve avonturen met ronkende namen zoals MountainbiKing, Sturm und Drank, Machoweekend,

Tour de Frantz en vele andere exploten, waarbij ik het aan jullie verbeeldingskracht overlaat wat

deze ontspanningsmomenten precies inhielden. Ook proost en merci aan alle medebourgondiërs

voor avondvullend vertier in duistere kroegen, na een … (goedgevulde/saaie/verrijkende/leerrijke/

vermoeiende/boeiende/vrije keuze) werkdag. In elk geval verdienen de scouts en alle vrienden die ik

eraan overhield een speciale vermelding, omdat scouting mijn zin voor avonturen en het buitenleven

aanwakkerde en mij liet ontbolsteren van leiding tot stam om ten slotte helemaal te ontwortelen.

Ook de dichtste vrienden komen op dit podium: Joris, kompaan van vele strijden en natuurlijk ook

de Fellowship met reisgenoten Rik en Foef en helaas algauw zonder Aki. De challenging trophee is nu

eventjes de mijne, neem ik aan? Welbedankt, aangenaam gezelschap!

Ik wil graag de thesisstudenten en proefpersonen bedanken die uiteraard een belangrijk aandeel

hadden bij het tot stand komen van dit onderzoek. Dat dit boekje er zo ongewoon stijlvol uitziet heb ik

te danken aan twee talenten: Bert voor de schitterende lay-out die hij aan dit boekje gaf en Evelien voor

de prachtige illustraties en nog zoveel meer (zie hier een beetje verder).

Ik wil ook uiteraard mijn ouders bedanken. Niet alleen omwille van het feit dat ze niet twijfelden aan

mijn LO- en andere keuzes en mij de kans boden mij ten volle te ontwikkelen, maar ook zeker omdat

ik heel goed besef dat ik onder andere de schrijverscapaciteiten van mijn vader en het enthousiasme

voor de wetenschap van mijn moeder geërfd heb, waarvoor dank.

En dan natuurlijk Evelien, ik denk dat je de ‘special price’ meer dan waard bent. Mij op sleeptouw

nemen en mijn leven verrijken, mij onder dompelen in een gezellige omgeving, de variëteit: cultuur, sport,

reizen, gedrevenheid… merci…

12

9,&,'_&"'J_&,%#'T#&"01%[0,*#,&*#3#)0#*M&GS&$.'%*&31883&8-&K1%V#.%VS&$J#.#,+&)#*&+#&

T001+#,&K8,&)%V,&-8K01%#*#&(81+X&bThe road in front of me is long and it is wide, I’ve got

()*"+,"-((,)./0$)1",)2,)"')34)52*$6).7)4"8)(-$)92&&2'1)9$&&).),:2';)./3)<8(&2#$*=)('*)92,:),:25)

doctoraat I’ve gotta take the ride…’

13

6^ECE:B9

Imagine your son as a goal keeper preparing himself to stop a

long-distance shot in the very last minutes of a soccer tournament

(if you don’t have a son, imagine harder). What is going around in

that little head? Will he imagine a die-hard ball in the right corner,

typically for that opponent? Will this advance knowledge have an

"+@2/+#/)%+)."0)02E0/>2/+-)0*8/F)C$)"0)"-):20-)*)!*--/$)%4)'%%9"+6)*-)

the right location and acting adequately? The present thesis attempts

-%)3$%8"7/)0%!/)*+01/$0)-%)-."0)>2/0-"%+)"+)*)!%$/)4%$!*'()0#"/+-"&#)

way. All you can do is just cheer loudly...

6@^!&>X

:9;9^@C&G;!^E4BA!GE;

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GENERAL INTRODUCTION

18

PART IPART IPART I

1. One-handed catching as a tool to study human motor behaviour

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85*%0,$_&%,&58$'&0,#N"8,+#+&(8..&58*5"%,3M&G,*#15#J*%0,&%$&J1#$#,*#+&8$&8&'$#-'.&K#"%5.#&-01&

*"#01#*%58.& 50,$%+#18*%0,$&0,& *"#&1#.8*%0,$"%J&(#*T##,& %,-01)8*%0,&8,+&)0K#)#,*_& 8$&

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,8*'18.&d%M#M_&+8%.7N.%-#&85*%K%*%#$e&8,+&$0)#*%)#$&',,8*'18.&d#M3M_&$J#5%/5&$J01*$&$%*'8*%0,$e&

5%15')$*8,5#$M&B,50,$*18%,#+&58*5"%,3&%,&J81*%5'.81&%$&-01T81+#+&8$&8,&8JJ10J1%8*#&*8$S&

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%,*#1,8..7NJ85#+&308.N+%1#5*#+&)0K#)#,*$&d#M3M_&1#85"%,3_&318$J%,3_&8%)%,3_&01&J0%,*%,3&8*&

$*8*%0,817&0(V#5*$eM&

How do we move? The present thesis is, in its most broad perspective, centred around this question,

and thus how the human system interacts with its environment. This seemingly straightforward question

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psychology and philosophy. However, the domain that perhaps attempts to coalesce the body of

knowledge is human motor control. Interception is an aspect of human motor control that can be

7/&+/7)*0)-./)#%%$7"+*-"%+)E/-1//+)*)3/$4%$!/$G0)E%7,)H%$)*+)"!3'/!/+-)02#.)*0)"+)$*#9/-)03%$-0)

or baseball batting), and an object, surface, gap or target area in the environment (Davids et al. 2002a).

Accordingly, research on interceptive behaviour has not been limited to catching or hitting a ball as

featured in many fast ball sports (e.g., tennis, goal keeping, baseball, cricket, hockey, handball), but has also

considered motor control of daily-life activities such as braking to avoid a rear-end collision (Tijtgat et

al. 2008), crossing a street (Oudejans et al. 1996) or even hitting crawling spiders (Brenner et al. 1998).

Apart from the practical relevance of studying this particular domain of motor control, interception :9;9^@C&G;!^E4BA!GE;

19

can also be considered as a useful vehicle for theoretical considerations on the relationship between

information and movement in goal directed behaviour (Williams et al. 1999; Davids et al. 2002a; Caljouw

/-)*'5)IJJK*L5)M'-.%26.)-./)#2$$/+-)-./0"0)1*0)+%-)"+-/+7/7)-%)-/0-)*)03/#"&#)!%-%$)#%+-$%')-./%$,()-./)

&+7"+60)7%).*8/)$/'/8*+#/)-%)-./%$/-"#*')2+7/$3"++"+60)%4)8"02%!%-%$)E/.*8"%2$5

Because of their highly constrained spatio-temporal requirements, interceptive actions are

distinguished from a broad range of internally-paced actions such as reaching, aiming, pointing and

grasping at stationary objects1 (see Table 1). The latter tasks have a rich research tradition that improved

understanding of how the human system is able to plan and control voluntary movements (e.g.,

Woodworth 1899; Jeannerod et al. 1995; Glover 2004; Elliott et al. 2010). However, it remains to be

#'*$"&/7)"4)-./)0*!/)3$"+#"3'/0)4%2+7)"+)-.%0/)-*090)*$/)*'0%)*33'"#*E'/)-%)/N-/$+*'',D3*#/7)"+-/$#/3-"8/)

behaviour. An important difference between interceptive and reaching or grasping tasks is the self-

paced nature of the latter. In grasping and reaching experiments, participants can generally decide by

themselves when to start the action and at what speed the limb is moved, which means that movement

execution is entirely internally imposed. The observation that visual feedback of the hand contributes

less to the control of catching than grasping, indicates that different control processes are likely to be

"+8%'8/7)"+)E%-.)-*090)HO#./+9)/-)*'5)IJJKL()*'-.%26.)*)#%!!%+)&+*')6$*03)#%+-$%').*0)$/#/+-',)E//+)

suggested (van de Kamp et al. 2011). In aiming experiments, participants usually have to react on a

(visual or auditory) trigger ‘as accurate and/or as quick as possible’. Note, however, that these imposed

instructions are not inherent in the task requirements itself, so that priority to temporal demands will

result in reaction and movement times ‘as short as possible’, whereas higher accuracy demands will

afford longer timing (Fitts and Peterson 1964). Interceptive actions like one-handed catching differ from

-./0/)4%$!/$)-*090)"+)-./"$)$/>2"$/!/+-)-%)/0-*E'"0.)*+7)!*"+-*"+)*)03/#"&#)03*-"%-/!3%$*')$/'*-"%+0."3)

E/-1//+)-./)*33$%*#."+6)%E:/#-)*+7)-./)$/03%+7"+6)/44/#-%$5)O3/#"&#*'',()-./).*+7)"0)-%)E/)3'*#/7)*-)-./)

$/>2"$/7)03*-"*')'%#*-"%+)*-)-./)$"6.-)!%!/+-()02#.)-.*-)-./)&+6/$0)#*+)E/)#'%0/7)*$%2+7)-./)E*'')*-)-./)

appropriate moment in time (Savelsbergh et al. 1992). Not only is coordination between body parts,

joints and limb segments required; but also between key limbs (the hand) and the moving target object

(the ball) in the environment, with the additional constraint of anticipating the impact of the ball on the

hand (Davids et al. 2002b). The current thesis considers whether the theoretical control mechanisms

20

PART IPART I

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Table 1. !"#$%"&'()*+',+"'-)*.)'/$',"#'012%) 12343)20()15'",)652,261',"31"63)'#$523"7"08)62165"08)23)2)

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"3)0*1)2%-2:3)31,2"851.*,-2,(

Next to differences with the abovementioned internally-paced tasks, catching can also be distinguished

from the interceptive task of hitting (Table 1). Indeed, catching adds to a hitting action such that: “the

transport component of a hitting action needs to be coordinated with a grasp component in catching”

HP%%-0!*)*+7)Q/3/$)RSSI()35)ISTL5)U."0)#'%0"+6)!/#.*+"0!)%4)-./)&+6/$0)*+7)-.2!E).*0)-%)0-*$-)*-)*)

certain time instant before the ball contacts the hand (Alderson et al. 1974), because in a purely reactive

0"-2*-"%+)H"5/5()1*"-"+6)4%$)-*#-"'/)"+4%$!*-"%+)%4)E*''D.*+7)#%+-*#-L()-./)&+6/$0)1%2'7)#'%0/)-%%)'*-/)*+7)

the ball would rebound out of the hand. The implication is that it is necessary in one-handed catching

to predict the future relationship between the hand and ball in order to achieve a successful grasp

(Bubic et al. 2010). While the anticipatory grasp in catching still requires a considerable anticipatory

1 For reasons of clarity, the 7/&+"-"%+) %4) "+-/$#/3-"8/)actions is narrowed from here on to externally-paced movements towards moving objects in contrast to internally-paced movements towards stationary objects. It should be acknowledged that this is a 0"!3'"&#*-"%+)%4)*)#%!3'/N)$/*'"-,)in which internally-paced actions might also require extrinsic timing in some cases, e.g., the overhand volleyball serve (Davids et al. 2001a).

:9;9^@C&G;!^E4BA!GE;

21

-"!"+6)#%!3%+/+-)/8/+)1./+)-./)-"!/)#%+0-$*"+-0)*$/)+%-)3*$-"#2'*$',)7/!*+7"+6().*8"+6)024&#"/+-)-"!/)

largely facilitates slow hitting actions (Montagne et al. 1993).

However, hitting actions in fast ball sports often have a time window that is shorter than for catching

(Bootsma and Vanwieringen 1990; Butcher 2001; Gray 2002a). This is assumed to have implications for

the control mechanisms at play. Hitting has been suggested to be more plan-based or program-based

under high temporal constraints than catching, with standard responses and less or even no time for on-

line control (Tresilian 2004; Tresilian and Houseman 2005; van Soest et al. 2010); N.B., on-line corrections

have been observed for very fast hitting movements (Brenner and Smeets 1997). Moreover, it should

be noted that the focus in many hitting and other interception tasks was the temporal regulation of

the interception, which in contrast to catching, only requires the participant to make contact with

a moving target, and thus not consider additional externally imposed impact requirements (e.g., by

'%#*-"%+)03/#"&#*-"%+L2.

Taken together, the study of one-handed catching as interceptive behaviour is acknowledged as

a useful tool for the study of human motor control - both in terms of daily-life activities and sports

- as well as for making theoretical considerations on how goal-directed behaviour is organized. The

externally-paced nature of interceptive actions provides a unique opportunity to study spatiotemporal

#%%$7"+*-"%+)!/#.*+"0!0()1"-.)#*-#."+6)"+)3*$-"#2'*$()7/!*+7"+6)3$/#"0/)&+/D-2+"+6)%4)-"!"+6)%4).*+7)

closure compared to only impacting the target as in hitting. Taking these complicated factors into

consideration, it can seem surprising to the naïve observer that children develop the skill of one-handed

catching automatically and seemingly without much effort. The adroitness of the human system to adapt

-%)/N3/$"!/+-*')!*+"32'*-"%+0)"0)/N/!3'"&/7)*+7)-./%$/-"#*'',)4$*!/7)"+)-./)+/N-)0/#-"%+5)

22

PART IPART IPART I

2. Adaptations to constraints in catching

G*& %$& %..'$*18*#+& (7& #)J%1%58.& #K%+#,5#& *"8*& *"#& "')8,& $7$*#)& %$& 8(.#& *0& 8+8J*& %*$&

)0K#)#,*&*0&$J#5%/5&50,$*18%,*$&8$&0'*.%,#+&(7&*"#&50,$*18%,*N(8$#+&8JJ1085"&0-&;#T#..M&

!"#&J1#$#,*&*"#$%$&50,5#,*18*#$&0,&8,&#.8(018*#+&K#1$%0,&0-&*"%$&8JJ1085"&T%*"&8&$J#5%8.&

#)J"8$%$&0,&*"#&%,Y'#,5#&0-&503,%*%0,&d(7&8+K8,5#&S,0T.#+3#e&8,+&J0$*'18.&8+V'$*)#,*$f&

*T0&8$J#5*$&*"8*&"8K#&1#5#%K#+&.#$$&8**#,*%0,&%,&.%*#18*'1#&0,&%,*#15#J*%K#&85*%0,$M&

In experiments that have sought to determine the instantaneous visual information sources used

for successful interception, it is common to manipulate the visual scene and/or ball properties and then

measure whether a catcher maintains successful performance with a different motor response. In the

current thesis, experimental manipulations will be seen as 6*031,2"013 and the appropriate changes in

motor response will be referred to as 2(2$121"*03. Constraints can be viewed as boundaries and features

that limit motion or make it happen. Newell (1986) organised them into organismic, environmental and

task constraints (see Fig. 1). The different constraints are said to interact to determine the search for an

optimal movement pattern of coordination and control3.

Figure 1. Constraints of organism (individual), task and environment

that specify the optimal pattern of coordination and control in the or-

ganization of movement (Adapted from Newell 1986)

2 It has been shown that different impact requirements in hitting can change the precise coupling between perception and action (Caljouw et al. 2004b)

3 Note however that ‘optimal movement pattern’ refers to the search for a stable pattern of coordination and control that accommodates the prevailing constraints and is hence changeable and not a &N/7) *+7) &+*') %3-"!*') 0%'2-"%+)since movement patterns by themselves are often suboptimal.

:9;9^@C&G;!^E4BA!GE;

23

>,820"3#"6)6*031,2"013 are related to the individual. For example, differences in kinematics between

catchers with weak stereopsis and their controls (Lenoir et al. 1999; Mazyn et al. 2004) have showed

how a defect in the visual system can constrain the way a catching task is approached. Next to these

structural aspects of organismic constraints, functional (time dependent) organismic constraints such

as intentions, emotions, decision-making and memory might invoke changes in movement coordination

(Glazier and Davids 2009). In particular, cognitive involvement through advance knowledge will be

elaborated in the present thesis.

?0+",*0#'012%)6*031,2"013 are properties of the environment such as gravity, temperature and natural

light that usually do not change over experimental set-ups. However, ball catching experiments with

changing background structure (Rosengren et al. 1988; Savelsbergh and Whiting 1988; Bennett et

al. 1999b,c; Montagne and Laurent 1994; van der Kamp et al. 1997) and even gravity circumstances

(McIntyre et al. 2001) have demonstrated that a changing environment induces adaptations of the

motor system. Based on the rationale that visual information is of major importance for interception

(see previous section), studies were developed that manipulated the visual environment during the

actual catching movement. Accordingly, it was shown that a catcher does not have to see the total ball

trajectory for successful catching (Whiting et al. 1970, 1973; Whiting and Sharp 1974; Sharp and Whiting

1974; Mazyn et al. 2007a) and that performance is maintained when intermittent visual samples are

separated by no more than approximately 80 ms (Bennett et al. 2003, 2004, 2006; Lyons et al. 1997;

Elliott et al. 1994; Olivier et al. 1998).

@234)6*031,2"013)#%+#/$+)-./)6%*')%4)-./)*#-"8"-,)H"5/5()#*-#."+6)%$)."--"+6L()-./)03/#"&#)$2'/0)*+7)-./)

physical properties of the task (Mazyn 2006). Manipulation of these task constraints leads to adaptations

"+)!%8/!/+-) E/.*8"%2$) *0) .*0) E//+) /N/!3'"&/7)E,) *'-/$*-"%+0) "+)!%8/!/+-) 9"+/!*-"#0)1./+)E*'')

properties such as size (Savelsbergh et al. 1991a; Jacobs and Michaels 2006; Servos and Goodale 1998;

van der Kamp et al. 1997), weight (Lang and Bastian 2001) or velocity (Williams and Macfarlane 1975;

Laurent et al. 1994; Caljouw et al. 2004a; Mazyn et al. 2006) were changed, or when the wrist was

mechanically perturbed in catching (Polman et al. 1996; Button et al. 2000).

24

PART IPART I

In a recent update of this constraints model (Newell and Jordan 2007), abovementioned ‘task’

constraints were categorized as environmental constraints (i.e., all physical boundary conditions external

to the organism), but for the present purpose, we will not digress in searching the most appropriate

categories of different constraints. More importantly, in this newer version of the constraints model it is

/!3.*0"</7)-.*-)V*0)!2#.)#%+0"7/$*-"%+)+//70)-%)E/)6"8/+)-%)-./)3%-/+-"*')"+@2/+#/)%4)-*09)#%+0-$*"+-0)

as to properties of the environment or the individual in the study of movement in action” (Newell and

Jordan, 2007, p. 22). The clear implication is that it might be premature to predict movement outcome

of certain perception-action couplings without taking the individual constraints of certain expectations

into account, as will be outlined below.

g!"#&$*'+7&0-&)0*01&50,*10.&)'$*&%,5.'+#&*"#&$*'+7&0-&503,%*%K#&J105#$$#$&8$&*"#7&1#.8*#&*0&

J#15#J*%0,&8,+&85*%0,Mh

!59#-2:;A**4)20()B**%%26*11)CDECF)$=)G=

In another recently reworking of the constraints-approach, Shumway-Cook and Woollacott (2012)

considered individual (i.e., the human equivalent of organismic) constraints as an interaction between

perception, action and cognition (see Fig. 2). As illustrated in all abovementioned experiments, the close

relationship between perception and action has been emphasized (see also Vonhofsten 1987) and

consequently investigated in the study of interceptive behaviour. However, it is our contention that the

"+@2/+#/)%4)#%6+"-"%+).*0)$/#/"8/7)!2#.)'/00)*--/+-"%+)"+)-."0)&/'7)%4)$/0/*$#.)H4%$)*+)/N#/3-"%+()0//)

Davids et al. 2001b). Therefore, the current thesis was developed to gain insights into how the cognitive

"+8%'8/!/+-)%4)*78*+#/)9+%1'/76/)!"6.-)"+@2/+#/)E*'')#*-#."+6)E/.*8"%2$5)M0)02#.()1/)7/&+/)#%6+"-"%+)

as 15')6*036"*93)$,*6'33)*.)'/$'6121"*0)1*-2,(3).919,')'+'013.

:9;9^@C&G;!^E4BA!GE;

25

Figure 2. Factors within the individual, the task and the environment that affect the organization of movement. The present

thesis will elaborate the cognitive factor of advance knowledge in the individual constraint and the stability factor of the task

constraint when catching a ball while standing. These focus points are highlighted in bold font. (Adapted from Shumway-Cook

and Woollacott 2012)

26

PART IPART I

At the level of task constraints, next to direct task manipulations, mobility and stability were designated

as constraining the movement at hand (Fig. 2). In terms of mobility, the continuous control mechanism

of locomotion towards the ball has been intensively investigated (e.g., Chapman 1968; Dannemiller et al.

1996; Lenoir et al. 2002; McBeath et al. 1995) and will not be treated in the present thesis. Importantly,

however, the stability requirements of catching a ball when standing has not been investigated in depth.

Moreover, many ball catching experiments were conducted in a seated position (i.e., Savelsbergh et al.

1991a; Caljouw et al. 2004a; Dessing et al. 2005), thereby eliminating the additional constraint of keeping

23$"6.-)E*'*+#/5)W/8/$-./'/00()0%!/)"+7"$/#-)"+7"#*-"%+0)4%$)-./)3%-/+-"*'',)"!3%$-*+-)"+@2/+#/)%4)3%0-2$*')

stability during catching have been shown (Rosengren et al. 1988; Davids et al. 2000; Angelakopoulos et

al. 2005; Savelsbergh et al. 2005). The role of postural adjustments while catching will be an important

theme of the current thesis and is further elaborated in section 5 of this introduction.

Taken together, the elaborated version of the constraint-approach of Newell (1986) permits a

theoretical framework to uncover some aspects that might have been overlooked in previous ball

#*-#."+6)'"-/$*-2$/X)-./)"+@2/+#/)%4)*78*+#/)9+%1'/76/)%+).*+7)9"+/!*-"#0)*+7)3%0-2$*')*7:20-!/+-0)"+)

catching. In the next section, different information sources that are believed to make catches successful,

are summarized.

:9;9^@C&G;!^E4BA!GE;

27

3. Information for catching

@,&0K#1K%#T& %$&3%K#,&0,&T"8*&S%,+&0-& %,-01)8*%0,& %$&'$#+& -01& %,*#15#J*%K#&85*%0,$M&

i%$'8.& %,-01)8*%0,&0-& *"#& (8..&T%..& (#& %+#,*%/#+& 8$& *"#&)8%,& 50,*1%('*01& *0& $'55#$$-'.&

%,*#15#J*%0,&8,+&*"#&J10)%,#,*&-',5*%0,&0-&J#15#J*%0,N85*%0,&50'J.%,3&T%..&(#&#)J"8$%[#+M&

i%$'8._&('*&8.$0&8'+%*017_&J10J1%05#J*%K#&8,+&*85*%.#&5'#$_&81#&$#,$017&$0'15#$&*"8*&J10K%+#&

%,$*8,*8,#0'$& %,-01)8*%0,& 0,& "0T& *0& )0K#M& H0T#K#1_& 0*"#1& %,-01)8*%0,& *"8*& %$& ,0*&

%,$*8,*8,#0'$.7&0(*8%,#+_&%$&%,*10+'5#+&8$&J0*#,*%8..7&%,Y'#,*%8.M&@+K8,5#&S,0T.#+3#_&8,&

%,-01)8*%0,&$0'15#&*"8*&%$&0(*8%,#+&J1%01&*0&*"#&/1$*&$#,$017&%,-01)8*%0,_&%$&+#$%3,8*#+&

8$&8&50))0,&*"#)#&%,&*"#&5'11#,*&*"#$%$M&

In order to catch successfully an actor has to reach out the upper limb and grasp the moving ball4.

U."0)7/!*+70)*)#/$-*"+)03*-"*')*+7)-/!3%$*')&+/D-2+"+6)%4)-./).*+7)-%1*$70)-./)E*'')"+)1."#.)3%0"-"%+)

and velocity of the ball together with an estimate of time before contact combine to shape the catching

movement (Dessing et al. 2005). The predominant information source to guide such behaviour is vision

(Williams et al. 1999). Research on interception has focussed on what kind of visual information is used

-%)3%0"-"%+)-./).*+7)*-)-./)$"6.-)3'*#/)*-)-./)$"6.-)-"!/()*+7)-./+)1./+)-%)#'%0/)-./)&+6/$0)*-)-./)$"6.-)

time to contact (TTC) so that the ball is grasped smoothly without fumbling out of the hand (Alderson

et al. 1974).

3.1. Optical variables for catching

Several sources of visual information are available in the optical array that might play a role in

the visuomotor guidance of successful interception. For a comprehensive discussion of these visual

information sources and empirical validity for their use in interception, the interested reader is referred

28

PART IPART I

-%)0%!/)/N#/''/+-)$/8"/10)%+)-."0)-%3"#)HY/6*+)RSSZ[)\*6%)/-)*'5)IJJSL5)]%$/)03/#"&#*'',()-.%0/)8"02*')

correlates important for being at the right time at the right place (i.e., to catch a ball) were stipulated

by Gray and Sieffert (2005). In this section, we will constrain ourselves to some examples of real ball

catching experiments that intended to discover which visual information sources enable interception.

Although not exhaustive, monocular (one eye) optical sources of information for interception

guidance are optical image size (the angle subtended by the ball) and its expansion rate, tau (!, see

below), optical gap (the angle between the ball, hand and eye) and its rate of change, angular location

(in reference to the horizontal, especially for falling balls) and approach speed of the ball (Fig. 3).

Figure 3. Monocular optical variables potentially involved in catching. ! is the angle subtended by the ball

and the front nodal point of the eye. " is the angle between ball, the hand and the eye (optical gap). #$is

the angle subtended by the ball’s centre relative to the horizontal (angular location). (Adapted from Zago et

al. 2009)

4 Note that at the same time, the catcher has the seemingly simple but additional requisite of keeping the body in balance, a topic that had remarkably less attention in catching literature, but will be deliberately addressed in section 5 of this introduction.

:9;9^@C&G;!^E4BA!GE;

29

^0"+6)*)E*'')-.*-)7/@*-/7)*0)"-)*33$%*#./7)-%)-./)#*-#./$()0%!/)E*'')#*-#."+6)/N3/$"!/+-0)0266/0-/7)

that the timing of grasp closure for catching is regulated by the ratio of the ball’s image size to the rate

of change of size, known as the optical variable tau (Savelsbergh et al. 1991a, 1993). This particular visual

3*$*!/-/$)3'*,/7)*)0"6+"&#*+-)$%'/)"+)3*0-)!%-%$)#%+-$%')'"-/$*-2$/)E/#*20/)"-)-$"66/$/7)*)&/$#/)7/E*-/)

%+)-./)-./%$/-"#*')6$%2+7"+60)%4)-."0),%2+6)&/'7)%4)$/0/*$#.)H0//)P%N)R)4%$)!%$/)"+4%$!*-"%+)*E%2-)-./)

optical variable tau).

Next to monocular visual cues, binocular visual information sources such as binocular disparity and

its rate of change, ocular vergence and binocular retinal image information aid successful performance, as

/8"7/+#/7)E,)-./)&+7"+6)-.*-)#*-#."+6)3/$4%$!*+#/)7/-/$"%$*-/7)4%$)!%+%#2'*$)#%!3*$/7)-%)E"+%#2'*$)

viewing (Vonhofsten et al. 1992; van der Kamp et al. 1997; Montagne et al. 1993). Binocular cues for

BOX 1. THE RISE AND FALL OF TAU

The optical variable tau or the ratio of image size and expansion velocity is considered as a direct estimate of the time before contact with a target will occur (TTC). Tau does not require computations (e.g., distance and velocity of the approaching ball) and has therefore become a paradigm example of J.J. Gibson’s ecological psychology (Gibson 1979). In this approach, all information required for catching is entirely present in surrounding structured light and thus available for direct perception. Although tau has been argued to guide brake behaviour (Lee 1976), interceptive hitting (Lee et al. 1983; Bootsma and Vanwieringen 1990) and catching (see main text), the exclusive use of this %3-"#*')8*$"*E'/).*0)E//+)4*'0"&/7)HU$/0"'"*+)RSSJ()RSS_()RSSK()RSSS*(E[)O!//-0()/-)*'5)RSSTL5)A!3%$-*+-)arguments against tau-guidance are the requirements that the ball approaches the eye directly and at constant speed, in addition to empirical evidence for the use of binocular information sources for TTC judgements (see main text). In conclusion, Gibson’s idea that in normal conditions the "+4%$!*-"%+)*8*"'*E'/) "+) -./)0-"!2'20) "0) 024&#"/+-) 4%$)*7/>2*-/)3/$#/3-"%+() "0)6/+/$*'',)*33$/#"*-/7)*!%+6)$/0/*$#./$05);%1/8/$()-./)/N"0-/+#/)*+7)"7/+-"&#*-"%+)%4)"+8*$"*+-0)H02#.)*0)-*2L)"+)#%+-$*0-)to time-varying use of many visual cues, and direct versus indirect perception continues the debate on how the visuomotor guidance of a catching task is regulated (see e.g., Michaels and Carello 1981; Lee 2009; Zago et al. 2009).

30

PART IPART I

catching were further investigated by experiments with a telestereoscope, a device that increased

interocular distance, and hence convergence and (absolute as well as relative) disparity (Judge and

Bradford 1988; Bennett et al. 1999a, 2000; van der Kamp et al. 1999; Savelsbergh and van der Kamp

2000). Absolute disparity or the difference in ball location between the left and right eye was suggested

to be involved in catches that were executed in the dark (Bennett et al. 1999a; van der Kamp et al.

1999), whereas differences between a dark and illuminated environment pointed to the contribution

of relative disparity (in relation to its background) in the timing of one-handed catching (Savelsbergh

*+7)8*+)7/$)`*!3)IJJJL5)a"+*'',()-./)&+7"+6)%4)'%1/$)3/$4%$!*+#/)-%6/-./$)1"-.)7"44/$/+-)!%8/!/+-)

kinematics for catchers with poor compared to good stereo vision (depth perception), endorses the

use of binocular information sources for the control of interceptive actions (Lenoir et al. 1999; Mazyn

et al. 2004, 2007a).

The aforementioned visual cues are suggested to contribute separately, or in combination with

other visual cues, to the visual information that guides interception (Rushton and Wann 1999; van der

Kamp et al. 1999; Zago et al. 2009). However, the question remains how these instantaneous information

sources are actually used to move the hand towards the ball. As an extension to separate estimates

of ball location and time of contact (i.e., to predict when to be where), a servo-controlling mechanism

has been suggested by which velocity of the lateral hand movement is continuously adjusted to the

3/$#/3-2*'',)03/#"&/7)$/>2"$/7)8/'%#"-,)H"5/5()7"8"7"+6)/0-"!*-/7)'*-/$*')7"44/$/+#/)E/-1//+)E*'')*+7).*+7)

through estimated TTC). Notwithstanding the attractiveness of this required velocity model (Peper et

al. 1994; Montagne et al. 1999, 2000), and its enhancements (Dessing et al. 2002, 2005), in showing a

close and continuous coupling between visual information and hand movements, it remains unclear if

this mechanism can be generalized to three-dimensional unconstrained catching movements that are

performed in daily life (Gray and Sieffert 2005; Tijtgat et al. 2009).

Clearly, then, there is a close relationship between what ball catchers perceive and how they respond

to this with a motor act. This close perception-action coupling has been recognized as an important

mechanism in interceptive behaviour (Williams et al. 1999). However, it is important to consider that

"7/+-"4,"+6)-./)8"02*')"+32-)8*$"*E'/0)-.*-)*$/)7/#"0"8/)"+)02##/0042')3/$4%$!*+#/)"0)%+',)-./)&$0-)0-/3)"+) :9;9^@C&G;!^E4BA!GE;

31

fully understanding the functioning of the visuomotor system. While direct perception-action coupling

elegantly illustrates how a catcher is able to respond (motor output) to instantaneous visual perception,

it remains equally critical to acknowledge how these transformations are guided by relevant neuro-

anatomical, neurophysiological and musculo-skeletal properties of the human action system (Tresilian

1999b; Beek et al. 2003). Further attempts to unravel the underlying mechanisms of these ‘black boxes’

is, and will be, an important goal for future research in interceptive behaviour.

3.2. Non-visual information sources

Since vision is considered as the most dominant sensory channel for human behaviour (Schmidt

*+7)B//)IJJbL)*+7)/03/#"*'',)4%$)3/$#/"8"+6)-./)@"6.-)#.*$*#-/$"0-"#0)%4)*)E*'')Ha"0#.!*+)*+7)O#.+/"7/$)

1985), it is obvious that most of the experiments on interception are directed towards the use of visual

information. However, it should be noted that other, non-visual sources of instantaneous information

could contribute to interception control. Next to vision, the presence or absence of auditory information

(e.g., a warning beep, the sound generated by ball release of a ball-projection machine or the noise of

a baseball bat whizzing trough the air) has been shown to change movement outcome for interception

(Savelsbergh et al. 1991b; Lacquaniti and Maioli 1989a; Button 2002; Tresilian and Plooy 2006)5. In the

case of visual suppression of the catching limb, an experienced catcher can rely on proprioceptive

information of the suppressed hand (Rosengren et al. 1988; Bennett, et al. 1999b,c; Fischman and

Schneider 1985). Also, the absence of visual information can be substituted by kinaesthetic and cutaneous

information for falling balls (Lacquaniti and Maioli 1989a). So together with visual information, auditory

cues can provided a goal keeper with instantaneous sensory information on the ball trajectory, while

proprioceptive and tactile information might be involved in the control of the interception.

However, as a totally different - for not being instantaneously available - information source, 2(+206')

40*-%'(8' has received much less attention in the study of interceptive behaviour. Advance knowledge

"0)"+)/00/+#/)*8*"'*E'/)E/4%$/)-./)&$0-)0/+0%$,)"+4%$!*-"%+)"0)%E-*"+/75)U./)/44/#-)%4)*78*+#/)"+4%$!*-"%+)

on human movement has previously been observed by changing gait patterns when walking on a dry

32

PART IPART I

#%!3*$/7)-%)*)3%-/+-"*'',)0'"33/$,)@%%$)Hc.*!)*+7)Y/74/$+)IJJI[)]*$"6%'7)*+7)Q*-'*)IJJI[);/"7/+)/-)

al. 2006), a more scaled postural response when participants repeatedly felt the ground shifting beneath

their feet (Horak et al. 1989), as well as different hand kinematics when participants are certain that

they have to aim at a particular location with or without vision (Hansen et al. 2006). In general, this

advance knowledge was gathered through the repetition of trials of the same condition such as blocks

of a repeating backwards perturbation, or by explicitly announcing what kind of trial there might be

expected (e.g., “the next walking trial will be slippery”; Marigold and Patla 2002). Traditionally, these

*78*+#/)9+%1'/76/)/44/#-0).*8/)E//+)"7/+-"&/7)*0)4*#"'"-*-"+6)4//74%$1*$7)!%8/!/+-)#%+-$%')HP2E"#)

et al. 2010; Elliott et al. 2010). However, from an ecological perspective, advance knowledge has been

interpreted as a form of intentional information that emerges under the various constraints related

-%)-./)03/#"&#)3/$4%$!*+#/)#%+-/N-)Hd*8"70)/-)*'5)IJJREL5);%1)7"44/$/+-)4%$!0)%4)+%+D"+0-*+-*+/%20)

*78*+#/)9+%1'/76/)!"6.-)"+@2/+#/)"+-/$#/3-"8/)E/.*8"%2$)"0)*)#%$/)-./!/)"+)-./)3$/0/+-)-./0"0)*+7)1"'')

be further explored in the next section.

5 Nevertheless, since the "+@2/+#/)%4)*27"-%$,)"+4%$!*-"%+)was beyond the scope of the current thesis, it was decided to minimize possible auditory information in the present experiments by wearing sound-masking headphones.

:9;9^@C&G;!^E4BA!GE;

33

4. Advance knowledge effects

!"%$& $#5*%0,& 0'*.%,#$& T"7& 8& $'($*8,*%8.& J81*& 0-& *"%$& *"#$%$& 50,5#,*18*#$& 0,& *"#&

%,K#$*%38*%0,&0-&8+K8,5#&S,0T.#+3#&d8$&8&-',5*%0,8.&%,+%K%+'8.&50,$*18%,*e&%,&%,*#15#J*%K#&

85*%0,$M&?%1$*_&%*&%$&$"0T,&*"8*&8+K8,5#&S,0T.#+3#&%,Y'#,5#$&*"#&)0K#)#,*&0'*50)#&0-&

$#K#18.&$#.-NJ85#+&*8$S$M&I#50,+_&%*&$"0'.+&(#&,0*#+&*"8*&*"%$&%,Y'#,5#&"8$&(##,&.813#.7&

0K#1.00S#+&%,&J1#K%0'$&.%*#18*'1#&0,&%,*#15#J*%0,&8,+&5#1*8%,.7&0,&58*5"%,3M&?%,8..7_&$0)#&

$J81$#&#K%+#,5#&0-&1#5#,*&#ZJ#1%)#,*$&0,&8+K8,5#&S,0T.#+3#&%,&%,*#15#J*%K#&85*%0,$&%$&

+#$51%(#+M

g!"#&10.#&0-&503,%*%K#&J105#$$%,3&%,&*"#&50,*10.&0-&K%$'8..7&3'%+#+&85*%0,&%$&0-*#,&0K#1.00S#+M&G,&-85*_&

)0$*&#ZJ#1%)#,*$&%,&*"%$&81#8&81#&+#.%(#18*#.7&+#$%3,#+&*0&1#)0K#&#ZJ#5*8,57&8,+&)#)017&#--#5*$&

*"10'3"&18,+0)%[8*%0,&0-&50,+%*%0,$&8,+&*0&*"#&'$#&0-&',-8)%.%81&0(V#5*$&0'*&0-&50,*#Z*M&!"#$#&"%3".7&

50,*10..#+&.8(018*017&50,+%*%0,$&dconstraints, authors notee&1#)0K#&)8,7&0-&*"#&1#3'.81%*%#$&*"8*&81#&

8K8%.8(.#&T"#,&J#0J.#&J#1-01)&85*%0,$&%,&*"#&1#8.&T01.+M&?01&#Z8)J.#_&%,&)8,7&$%*'8*%0,$&%,&T"%5"&

J#0J.#&81#&1#2'%1#+&*0&%,*#15#J*&8,&8JJ1085"%,3&0(V#5*&d#M3M_&T"#,&J.87%,3&(8$#(8..&01&-00*(8..e_&*"#&

0(V#5*&"8$&8&-8)%.%81&$%[#&8,+&*18K#.$&8*&8&J1#+%5*8(.#&$J##+M&D#*&%,&J$75"0J"7$%58.&#ZJ#1%)#,*$&0,&

!!A_&%*&%$&,#5#$$817&*0&K817&0(V#5*&$J##+&8,+&0(V#5*&$%[#&0K#1&8&.813#&18,3#Mh&

H,2:)CDDC2F)$=)EEIJ=

U./)*E%8/)#"-*-"%+)"+7"#*-/0).%1)-./)"+@2/+#/)%4)*78*+#/)9+%1'/76/)%+)"+-/$#/3-"8/)*#-"%+0)!"6.-)

have been underestimated in previous experimental methodologies. Notwithstanding their merits in

gaining insights in the functioning of the visuomotor system, it is remarkable that the potential effect

of advance knowledge on a catching movement has received so little attention. On the one hand,

34

PART IPART I

memorized information of previous trials together with expectancies of the upcoming trial is suggested

to be common in sports situations and other daily-life contexts under investigation, indicating that

a predictable context such as a blocked-order experimental set-up has relevance. This is intuitively

/N/!3'"&/7)E,)V3$/7"#-*E'/) -$*:/#-%$"/0) 4%$)!%8"+6)%E:/#-0) "+) -./) $/*')1%$'7e) HO/$8%0)*+7)=%%7*'/)

1998, p. 93) and the “predictable ball speed for ball sports” as cited above by Gray (2002a), although

aerodynamic effects of ball trajectories (Mehta and Pallis 2001) are suggested to induce randomness in

interceptive behaviour. On the other hand, studies that provided recognisable, recurrent task constraints

H/565()E,).*8"+6)*)E'%#9/7D%$7/$)7/0"6+L)!*9/)"-)7"4&#2'-)-%)7/-/$!"+/)1./-./$)-./)%E0/$8/7)%2-#%!/0)

were a function of intentional constraints on the part of the individual participants (i.e., advance

knowledge) or the task constraints imposed such as a changing ball speed and size (Davids et al. 2001b).

In fact, most of the studies on interceptive behaviour selected either a blocked-order (e.g., Mazyn et

al. 2006) or random-order (e.g., Caljouw et al. 2004a) design without explicitly taking into account the

above considerations. In the following paragraphs, it will be illustrated how advance knowledge effects

have stimulated a considerable number of studies in self-paced aiming actions. This will be followed by

an overview of the exceptional catching and hitting experiments that provide some evidence for the

effect of advance knowledge6.

4.1. Advance knowledge effects for self-paced actions: wide-spread evidence

In explaining movement control when visual feedback is present or absent, several studies on aiming

and grasping suggested that advance knowledge of such feedback will result in different movement

outcomes (Zelaznik et al. 1983; Elliott and Allard 1985; Khan et al. 2002; Heath et al. 2006; Neely et al.

2008). The effect of advance knowledge was investigated using a blocked-order versus random-order

experimental set-up7. It has been shown that a blocked-order situation (i.e., all trials of one block with

vision, another block without vision) leads to expectancies of the availability of visual feedback information.

These expectancies are referred to in the current thesis as "#$%"6"1)2(+206')40*-%'(8', since the exact

task condition (blocked-order or random-order) was not explicitly mentioned by the investigators,

but instead evolved through experiencing the same task conditions repeatedly. The expectancy-effect

6 Advance knowledge by visual anticipation based on the preparatory actions of the opposing player in sports contexts (see, e.g., Abernethy 1990; Savelsbergh et al. 2002; O."!)/-)*'5)IJJbL)"0)+%-)03/#"&#*'',)addressed in the current thesis.

7 In blocked order, there was a block with trial conditions AAAAAA than BBBBBB; in random order, trial conditions were, e.g., AABABB than BABBAA.

:9;9^@C&G;!^E4BA!GE;

35

refers to conscious information about the future trial acting as a cognitive mediator towards the most

appropriate movement strategy. If participants know for certain that visual feedback will be provided, an

online mode of control is preferred. In the case of unavailable or unreliable visual information, however,

-./)!%8/!/+-)"0) "+"-"*-/7)1"-.)*)!%$/)%4@"+/)*+7)./+#/)4//74%$1*$7)!%7/)%4)#%+-$%')HW//',)/-)*'5)

2008). Nevertheless, an alternative explanation has been presented to elucidate differences between

blocked-order and random-order conditions. By showing that participants did not take advantage of

expectancy from previous trials in an additionally alternating condition8, it was suggested that the adjusted

movement execution in the blocked-order condition expressed a particular effect of trial-by-trial history

through cumulative learning based on recent repetitive experiences rather than a cognitively mediated

movement strategy (Song and Nakayama 2007; Whitwell et al. 2008; Whitwell and Goodale 2009). Our

approach is that trial-by-trial history can also be categorized as a form of implicit advance knowledge,

clearly establishing a non-instantaneous guidance that does not appear from direct sensory information,

but from experience. Note in this respect that we would not necessarily classify advance knowledge as

*+)/N#'20"8/)."6.)#%!32-*-"%+*')E$*"+)#%+0-$2#-()E2-)$*-./$)*0)*)E$%*7',)7/&+/7)!/#.*+"0!)/N3$/00"+6)

how information that does not belong to the properties of the isolated trial (instantaneous sensory

"+4%$!*-"%+L)!"6.-)"+@2/+#/)!%-%$)E/.*8"%2$)H0//)*'0%)B%3/<D]%'"+/$)/-)*'5)IJJZL5

Other experiments tested the effect of advance knowledge by explicitly precueing certain task

conditions. This '/$%"6"1) 2(+206') 40*-%'(8' was presented in a random context so that the effect

of trial-by-trial history within a trial was minimized. For fast aiming or grasping movements, explicit

*78*+#/)"+4%$!*-"%+)%4)-./)03/#"&#)%2-#%!/)3*$*!/-/$0)H"5/5()7"$/#-"%+)%$)*!3'"-27/L)%4)-./)23#%!"+6)

movement (Rosenbaum 1980; Craighero et al. 1996, 1998; Olivier and Bard 2000; Mieschke et al. 2001;

Borysiuk and Sadowski 2007) or visual condition (Hansen et al. 2006) has been shown to result in a

shorter reaction time and adjusted movement execution. However, it is not clear whether the optimal

movement pattern for such self-paced actions, performed as quick as possible, would also apply to the

one-handed catching task under study (see also section 1). In the following paragraphs, some preliminary

indications are presented that implicit advance knowledge effects might affect catching behaviour and

one study is introduced that addressed explicit advance knowledge for catching.

36

PART IPART I

4.2. Advance knowledge effects for catching: preliminary indications

M+)"!3%$-*+-)*$62!/+-)4%$)*78*+#/)9+%1'/76/)/44/#-0)%+)#*-#."+6)%$"6"+*-/0)4$%!)-./)03/#"&#)#*0/)

of grasping a free falling ball with the outstretched arm (no transport is required). A free falling ball is

0-$%+6',)*##/'/$*-/7)E,)6$*8"-,)0%)-.*-)$/',"+6)/N#'20"8/',)%+)"+0-*+-*+/%20)&$0-D%$7/$)8"02*')"+4%$!*-"%+)

1%2'7) '/*7) -%) 02E0-*+-"*') /$$%$0() /03/#"*'',) #'%0/) -%) #%+-*#-) +/*$) -./) /+7)%4) E*'') @"6.-) H\*6%)/-) *'5)

2009). Evidence for the existence of an internal model based on advance knowledge of gravity has

been found for interception (e.g., Lacquaniti and Maioli 1989a; McIntyre et al. 2001; Zago et al. 2004;

Senot et al. 2005) and the representation of this gravitational motion has been attributed to the human

vestibular cortex (Indovina et al. 2005). However, the current thesis investigated ball trajectories that are

projected towards the participants shoulder with a straight or sometimes (pseudo)parabolic trajectory

that is subject to aerodynamic effects. Consequently, the suggested internalized model of gravitation is

presumed to be of less importance for such interceptions (see also Baures et al. 2007).

Interestingly, when catching under visual occlusions and there was uncertainty about the exact

72$*-"%+)%4)0//+)@"6.-()'/$'61206:)<'52+"*9, was argued to direct attention to the initial portion of the

@"6.-)-.*-)1*0)#/$-*"+',)8"0"E'/)HO.*$3)*+7)f."-"+6)RSZbL5)c%+8/$0/',()*78*+#/)9+%1'/76/)%4)-./)72$*-"%+)

of occlusion intervals during intermittent vision has been suggested not to affect catching performance

(Lyons et al. 1997). Nevertheless, since the latter results were restricted to performance outcome and

the possible effect of advance knowledge was not scrutinized at a kinematic level, it remains unclear to

1.*-)/N-/+-)-./)*#-2*')!%8/!/+-)#%%$7"+*-"%+)1*0)"+@2/+#/7)E,)*78*+#/)9+%1'/76/5)f./+)-./)1$"0-)

of the catching arm was mechanically perturbed unexpectedly during a catching action, the (incorrect)

expectation of a new perturbation in subsequent non-perturbed trials constrained participants to a

movement pattern similar to perturbation trials, thereby ignoring the instructions not to anticipate such

perturbations (Button et al. 2000). Therefore, implicitly gathered advance knowledge was suggested to

induce an intentional ‘squirt’ in the initial movement impulse.

To test this effect of advance knowledge on catching, Button et al. (2002) replicated their study of

wrist perturbation during catching, but with the introduction of an expected-unexpected paradigm.

8 In alternating order, the trial conditions changed alternately, i.e., ABABAB than ABABAB (Song and Nakayama 2007; Whitwell et al. 2008; Whitwell and Goodale 2009).

:9;9^@C&G;!^E4BA!GE;

37

Perturbations in the expected condition were preceded by a verbal warning, while in the unexpected

condition these perturbations appeared unannounced. Participants demonstrated different adaptations

between the expected and unexpected condition, with an anticipatory strategy suggested to be based

on explicit advance knowledge of perturbation. In the absence of advance knowledge of perturbation,

an opportunistic, tracking-based strategy was introduced to cope with sudden changes in constraints.

In hitting tasks, several studies indicated towards the effect of implicit (van Donkelaar et al. 1992;

Daum et al. 2007) and explicit (Teixeira et al. 2006; Marinovic et al. 2008) advance knowledge on

movement execution speed. For baseball batting, it has been shown that advance knowledge based

%+)3$/8"%20)3"-#./0)*+7)3"-#.)#%2+-)"+@2/+#/0)-./)-/!3%$*')*+7)03*-"*')*##2$*#,)%4)*)E*0/E*'')01"+6)

(Gray 2002a, 2002b). However, since different movement strategies are suggested between hitting

and catching (see section 1; Tresilian 2004), the role of advance knowledge in catching awaits further

empirical evidence.

The aforementioned studies provide some evidence that advance knowledge plays a role in shaping

the perception-action coupling based on instantaneous sensory information. A main purpose of the

present thesis was to further scrutinize how different types of advance knowledge affect the interceptive

behaviour for catching. The next section addresses an aspect that has reached little attention in the

study of interceptive behaviour, i.e., its postural control.

38

PART IPART I

5. Postural adjustments

@& 5.81%/58*%0,& %$& 3%K#,&T"7& J0$*'18.& 8+V'$*)#,*$& -01& %,*#15#J*%K#& 85*%0,$& +#$#1K#&

8& 5.0$#1& #Z8)%,8*%0,M& ^8%$%,3& *"#& 81)& -01& 58*5"%,3& %$& $'JJ0$#+& *0& %,+'5#& J0$*'18.&

8+V'$*)#,*$_& 8$& "8$& (##,& $"0T,& -01& $#K#18.& $#.-NJ85#+& 81)N18%$%,3& *8$S$M& H0T#K#1_& %*&

1#)8%,$&',5.#81&"0T&*"#$#&J0$*'18.&8+V'$*)#,*$&#K0.K#&-01&*"#&$J#5%/5&*8$S&50,$*18%,*$&

+'1%,3&%,*#15#J*%0,M&F01#0K#1_&*"#&10.#&0-&8+K8,5#&S,0T.#+3#&0,&J0$*'18.&8+V'$*)#,*$&

+'1%,3&%,*#15#J*%K#&85*%0,$&"8$&,0*&(##,&$*'+%#+&7#*M&!"#1#-01#&%*&1#)8%,$&',S,0T,&%-&8,+&

"0T&*"%$&T0'.+&%,Y'#,5#&J0$*'18.&50,*10.&-01&58*5"%,3M

g!T0&-',+8)#,*8.&2'#$*%0,$&.%#&8*&*"#&"#81*&0-&*"%$&/#.+&0-&$*'+7&dhuman motor control, authors

noteeM&E,#&%$&"0T&T#&50,*10.&0'1&)0K#)#,*$f&*"#&0*"#1&%$&"0T&T#&)8%,*8%,&$*8(%.%*7h

K*3'0<29#)ELLEF)$=)M=

5.1. Postural adjustments when raising the arm

Although maintaining stability has been largely acknowledged in the study of human movement

control (see above citation), it is remarkable that only sparse attention has been directed to the

additional stability requirements during interceptive behaviour. Although it has been emphasized that the

movement of the catching hand interacts with the ability to maintain a stable posture (Davids et al. 2000;

Angelakopoulos et al. 2005; Savelsbergh et al. 2005), the exact mechanism of such postural control

during catching has not yet been investigated. Interceptive actions such as catching typically require that

the arm is raised upwards and towards the ball so that postural adjustments are necessary to overcome

the disturbance of body posture (Bouisset and Do 2008). This raising of the arm disturbs the body for :9;9^@C&G;!^E4BA!GE;

39

two reasons. First, the moving segment causes a quick change of the geometry of the body which leads

to a small forward acceleration of centre of mass (COM). Second, the internal forces caused by the

muscle contraction to move the arm results in reaction forces on the supporting segments (Massion

1992). Notably,)201"6"$21*,:)$*319,2%)2(N931#'013)(APA) have been the subject of much research, typically

in a paradigm where the outstretched arm was raised (see Box 2 for more information of APA).

It remains to be examined, however, whether the same postural adjustments will also be applied for the

03/#"&#)-*09)#%+0-$*"+-0)%4)$*"0"+6)-./)*$!)"+)/N-/$+*'',D3*#/7)"+-/$#/3-"8/)*#-"%+0)*0)"+)#*-#."+65)W/N-)

to placing the hand at the right time at the required spatial location, catching also requires a control

of limb compliance to absorb ball momentum during the dynamic interaction between hand and ball

(Lacquaniti and Maioli 1989b; Lacquaniti et al. 1991, 1992), which may also impose postural adjustments.

BOX 2. APA: PREPARATORY EQUILIBRIUM CONTROL... OR JUST MOVEMENT SUPPORT?

Anticipatory postural adjustments (APA) typically occur simultaneously with, or just before, the initiation of a voluntary movement by a feedforward control mechanism (Cordo and Nashner 1982). g8"7/+#/)4%$)MQM)1*0)>2*+-"&/7)E,)%+0/-)%4)3%0-2$*')!20#'/0)*#-"8"-,)*+7)E*#91*$70)7"03'*#/!/+-)of centre of foot pressure (COP) before the start of the focal movement. Importantly, APA can vary "+)$/'*-"%+)-%)03/#"&#)-*09)#%+0-$*"+-0)HP%2"00/-)*+7)B/)P%</#)IJJIL5)a%$)/N*!3'/()-./)!*6+"-27/)and onset of APA has been shown to scale with movement speed and/or additional load (Horak et al. 1984; Lee et al. 1987; Bouisset et al. 2000; Bleuse et al. 2002, 2006; Mochizuki et al. 2004; Termoz et al. 2004; Zattara and Bouisset 1988). Moreover, APA occur earlier in self-paced than reaction-time arm raisings (Horak et al. 1984; De Wolf et al. 1998; Nougier et al. 1999; Berrigan et al. 2006; Bleuse et al. 2008). Whereas APA have been commonly attributed to overcome the upcoming postural disturbance (e.g., Bouisset and Zattara 1987), their function has recently been suggested to ensure segment stabilization (Pozzo et al. 2001; Patla et al. 2002). Based on computer simulations, it seemed unlikely that the observed initial small variations in COM movement in arm raising are accompanied by immediate postural compensations, because they do not involve a threat to balance (Loram and Lakie 2002).

PART I

40

PART IPART I

Indeed, APA in response to the expected and actual mechanical impulse of a load has been illustrated

when catching with the hand already outstretched at impact location (Shiratori and Latash 2001; Li and

Aruin 2007, 2009). Therefore, it was of interest here to scrutinize postural adjustments in response to

interceptive actions, since they are suggested to play a fundamental role for successful performance.

5.2. Advance knowledge effects on postural adjustments

Returning to advance knowledge effects (see section 4), it has been shown that prior knowledge of

*+)/N-/$+*')3/$-2$E*-"%+).*0)*+)"+@2/+#/)%+)3%0-2$*')#%+-$%')4%$)0-*+7"+6)E*'*+#/5)a%$)/N*!3'/()*78*+#/)

knowledge of the characteristics of a forthcoming displacement of the visual scene inhibited the visually

induced body sway and reduced postural re-adjustments (Guerraz et al. 2001; Freitas Junior and Barela

2004). Also, when surface perturbations were expected by using a blocked-order presentation (Horak

et al. 1989) or an auditory cue (McChesney et al. 1996), postural responses were reduced. However, the

task of the participants during these experiments was solely to maintain standing posture without an

*77"-"%+*')-*09)-%)E/)3/$4%$!/75)U./$/4%$/()"-)"0)+%-)#'/*$).%1)*78*+#/)9+%1'/76/)#%2'7)*'0%)"+@2/+#/)

the postural adjustments induced by an additional task such as catching. Indeed, since advance knowledge

"0)0266/0-/7)-%)3'*,)*+)"+@2/+-"*')$%'/)%+)!%8/!/+-)/N/#2-"%+)72$"+6)"+-/$#/3-"%+)H0//)0/#-"%+)KL)*+7)

on postural control for balance as outlined above, it remains to be determined if advance knowledge

would also affect postural adjustments during externally-paced upper limb movements such as catching.

:9;9^@C&G;!^E4BA!GE;

41

6. Outline of the thesis

The general purpose of the current thesis was to investigate how advance knowledge of task

#%+0-$*"+-0)"+@2/+#/0)!%-%$)E/.*8"%2$)72$"+6)#*-#."+6)!%8/!/+-05)A+)-./)/N3/$"!/+-0)%4)0-27,)R)*+7)

4, good ball catchers tried to catch as many balls as possible while the task constraint of ball speed was

manipulated. In study 1, advance knowledge effects were investigated by comparing arm kinematics

between catching at different ball speeds presented in a blocked or random order. Importantly,

observed differences could not only be induced by a change in cognitively mediated movement strategy

(expectation) based on implicit advance knowledge, but also by a trial-by-trial history effect (prepare

movement based on the preceding trials) that might have caused changes to the movement kinematics.

Therefore, in study 2, trials with explicit advance knowledge of impending visual occlusion (expected

condition) were compared with unexpected visual occlusion trials; both trial types were randomly

interspersed between normal vision trials. Again, differences between a situation with and without

advance knowledge could provide evidence if and how the human system is able to gear its movement

based on advance knowledge.

Moving the hand towards a target while standing demands postural adjustments. To date, however,

it is unknown how these postural adjustments evolve when catching while standing upright. Hence, in

study 3, a pilot study was performed to compare catching a ball at high speed to a well-documented

arm raising task. It was questioned how raising the arm for catching differs from raising. To measure

postural adjustments, a full-body capture of the movement was accompanied with kinetics of the

postural adjustments and measurements of postural muscle activation.

Next to differences in how the hand moves towards the object-to-be-intercepted (see study 1

and 2), it was questioned if advance knowledge also has an impact on postural adjustments to the

movement. In study 4, the blocked-random order paradigm was repeated to scrutinize how implicit

*78*+#/)9+%1'/76/)"+@2/+#/0)-./)"+-/$3'*,)E/-1//+)*$!)!%8/!/+-0)*+7)3%0-2$*')*7:20-!/+-0)72$"+6)

catching.

PART I

42

PART IPART I

!0&$'))81%[#_&*"#&1#$#815"&2'#$*%0,$&*"8*&T#1#&%,K#$*%38*#+&%,&*"#&01%3%,8.&1#$#815"&0-&*"#&J1#$#,*&*"#$%$&81#X[STUDY 1] ]"8*&%$&*"#&%,Y'#,5#&0-&%)J.%5%*&8+K8,5#&S,0T.#+3#&0-&(8..&$J##+&0,&)0K#)#,*&S%,#)8*%5$&%,&58*5"%,3j[STUDY 2] ]"8*& %$& *"#& %,Y'#,5#& 0-& #ZJ.%5%*& 8+K8,5#& S,0T.#+3#& 0-& K%$'8.&055.'$%0,&0,&)0K#)#,*&S%,#)8*%5$&%,&58*5"%,3j[STUDY 3]&]"8*&81#&*"#&J0$*'18.&8+V'$*)#,*$&-01&58*5"%,3j&H0T&+0&J0$*'18.&8+V'$*)#,*$&%,&58*5"%,3&+%--#1&-10)&J0$*'18.&8+V'$*)#,*$&%,&T#..N$*'+%#+&81)&18%$%,3&*8$S$j[STUDY 4]&&]"8*&%$&*"#&%,Y'#,5#&0-&%)J.%5%*&8+K8,5#&S,0T.#+3#&0-&(8..&$J##+&0,&*"#&%,*#1J.87&(#*T##,&81)&)0K#)#,*$&8,+&J0$*'18.&8+V'$*)#,*$&%,&58*5"%,3j

RESEARCH QUESTIONS

:9;9^@C&G;!^E4BA!GE;

43

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PART IPART I

:9;9^@C&G;!^E4BA!GE;

61

6@^!&<X

E^G:G;@C&^9I9@^AH

[ABSTRACT] The purpose of this experiment was to examine the effects of advance knowledge on the kinematics of one-handed catching. Balls were launched from a distance of 8.4 m by a ball-projection machine with adjustable launching speed. Fifteen skilled ball catchers caught 160 balls with their preferred hand under blocked-order (4 blocks, each comprising 20 trials at one of 4 different ball speeds) or ran-dom-order (4 blocks, each comprising 20 trials of 4 different ball speeds) conditions. P,)3$%:/#-"+6)E*''0)1"-.)7"44/$/+-)E*'') 03//70) 4$%!)*)&N/7)3%0"-"%+() "-)1*0)3%00"E'/)to modify the temporal constraints of the catching task. In both the blocked-order and random-order conditions, catching performance (number of catches, touches and misses) decreased with increasing temporal constraints. Analysis of successful trials indicated that this equal level of catching performance was achieved with different !%8/!/+-) 9"+/!*-"#05) O3/#"&#*'',() -./$/) 1*0) *) #.*+6/) "+)!%8/!/+-) -"!/() '*-/+#,()1$"0-)8/'%#"-,)3$%&'/()*+7)#%/4&#"/+-)%4)0-$*"6.-+/005)P*0/7)%+)/N3/#-*+#,)%4)3$/8"%20)trials, movement kinematics were scaled to ball speed in the blocked-order condition whereas in the random-order condition, participants exhibited a more default initial response. However, this latter mode of control was functional in that it increased the likelihood of success for the higher ball speeds while also providing participants with a larger temporal window to negotiate the unexpected temporal constraint on-line for the lowest ball speed.

[KEYWORDS] Ball catching; Advance knowledge, Blocked- versus random-order, Kinematics; Planning-control

BASED ON Tijtgat P, Bennett SJ, Savelsbergh GJP, De Clercq D, Lenoir M. (2010) Advance knowledge effects on kinematics of one-handed catching.)?/$',"#'012%)R,2"0)K'3'2,65F)CDE, 875-884

STUDY I: ADVANCE KNOWLEDGE EFFECTS ON

KINEMATICS OF ONE-HANDED CATCHING

PART II

64

PART IIPART II

I!B4D&GX&&@4i@;A9&L;E]C94:9&9??9A!I&E;&LG;9F@!GAI&E?&E;9NH@;494&A@!AHG;:&

INTRODUCTION

It is well documented that the human system is capable of taking advantage of advance knowledge

when performing motor tasks (Zago et al. 2009), and that this may emanate from different forms and/or

on different time scales. For instance, on a short time scale, it has been shown that precueing with advance

knowledge on direction and extent of motion (Rosenbaum 1980) or target location and impending

visual condition (Hansen et al. 2006) can facilitate rapid aiming tasks, whereas on a longer time scale (i.e.,

when more time passes between receiving advance knowledge and movement execution), advance

expectations can be formed based on the history of previous pitches in baseball hitting (Gray 2002a,

2002b). In the latter case, advance information regarding previous stimuli can be incorporated into an

internal model of the ball approach trajectory that facilitates successful performance of an interception

task (Zago et al. 2004; Senot et al. 2005; Lopez-Moliner et al. 2007). Recent work has suggested that

advance information processing during action preparation in a catching task has been located in the left

parietal posterior cortex (Nader et al. 2008).

Advance knowledge is also implicitly available when the task is completed in a predictable order,

and can lead to different interceptive behaviour as compared to an unpredictable order. In a study by

Daum et al. (2007), which required targets moving in a desktop virtual environment to be intercepted

with a haptic interface, it was found that a context of unpredictable target motion resulted in a higher

maximal interception speed. It was suggested that when advance knowledge of target direction was

absent (unpredictable), participants used a “#*,') ,"34:)20() %'33)2669,21')31,21'8:” (Daum et al. 2007,

p. 489) that involved attempting to match the interception object to the moving target as quickly as

possible in order to minimize the subsequent distance to the target after a possible change of direction.

Importantly, this type of motor control indicates that at least part of the response is prepared in advance I!B4D&G

65

of movement onset and hence is in contrast to the suggested exclusive reliance on continuous control

during interceptive actions (Bootsma et al. 1997; Montagne et al. 1999; Dessing et al. 2002).

One of the main advantages exhibited when provided with advance knowledge in aiming studies is

that it enables participants to modify temporal aspects of motor action. First, when advance knowledge

is provided regarding the number of items to be processed (i.e., which targets from a larger set should

be responded to), there is a reduction in reaction time (Khan et al. 2008). Second, by providing advance

knowledge on target location, it is possible to rely more on pre-planning of movement kinematics,

1."#.)"0)-./+)$/@/#-/7)"+)'/00)+//7)4%$)%+D'"+/)#%+-$%')*+7)*)$/72#-"%+)"+)!%8/!/+-)-"!/)HP%$,0"29)

and Sadowski 2007). However, it is important to note that a distinction has to be made between self-

paced motor tasks, in which participants are typically instructed to act as quickly and accurately as

they deem possible (Elliott and Allard 1985; Khan et al. 1998, 2002), and externally paced tasks such

*0) "+-/$#/3-"8/) *#-"%+0() 1."#.) $/>2"$/) *) 03/#"&#) 03*-"%-/!3%$*') $/'*-"%+0."3) E/-1//+) -./) *33$%*#.)

object and responding effector to be established and maintained. As a consequence of these different

timing constraints (i.e., internally vs. externally imposed), aiming for stationary objects is prone to a

speed-accuracy trade-off, whereby there is a shift in the amount that movement kinematics are planned

in advance or adjusted on-line. It remains to be determined, however, if the same mode of control

operates in a catching task, which has externally imposed temporal constraints. Recently, it has been

shown in two-dimensional interceptive hitting tasks that movement time and peak transport velocity

can be varied independently in order to meet the space-time accuracy demands imposed by different

target speeds and sizes (Tresilian et al. 2009). For example, participants can achieve better temporal

accuracy by maintaining a higher peak wrist velocity, even if there is an increase in overall movement

time. In the current study, it will be investigated if the same independent control strategy is present in a

three-dimensional catching task.

To date, studies on catching under different temporal constraints have shown that humans are

capable of adapting their movement kinematics to increasing ball speeds, although a decrease in catching

performance cannot be entirely overcome (Laurent et al. 1994; Mazyn et al. 2006). However, while

these studies used ball speeds up to 19.7 m/s (Mazyn et al. 2006) in order to challenge human catching PART II

66

PART IIPART II

abilities with extreme temporal constraints, it is relevant to remark that the different ball speeds were

received in a blocked-order. This methodological constraint may have facilitated a mode of control by

1."#.)*78*+#/)9+%1'/76/)%4)E*'')03//7)4$%!)-./)3$/#/7"+6)E*''0)1*0)"+#%$3%$*-/7)*+7)"+@2/+#/7)-./)

subsequent response. Therefore, it is not clear whether the decline in Latency time (LT) that occurred

with increasing temporal constraints was solely a consequence of the temporal constraint itself, or

whether an “'/1,2)a3b9",1c)*.)"01'01"*02%)"0.*,#21"*0” (Button et al. 2000, p. 28), which in this case would be

based on advance knowledge of the expected ball speed, had an effect on the information processing.

Likewise, one could ask if the observed relationship between an expected temporal constraint and

9"+/!*-"#)!/*02$/0)02#.)*0)!%8/!/+-)-"!/)HB*2$/+-)/-)*'5)RSSK[)]*<,+)/-)*'5)IJJTL()8/'%#"-,)3$%&'/)%4)

the wrist (Laurent et al. 1994) or rectilinearity of the wrist trajectory (Laurent et al. 1994; Mazyn et al.

2006) was not also biased by advance knowledge of ball speed. In this respect, it is relevant to note that

in a ball catching experiment with mechanical perturbations of the wrist, Button et al. (2002) found that

when advance knowledge of such a perturbation was announced, the wrist velocity had a higher peak

and occurred earlier during the unfolding of the catch.

Therefore, the purpose of the current experiment was to examine the effects of advance knowledge

on the kinematics of one-handed catching, which unlike internally paced aiming movements, is subject to

externally imposed temporal constraints that must be met while also satisfying severe spatial constraints

(i.e., high accuracy and precision of hand placement relative to the ball trajectory). To this end, a blocked-

order versus random-order design was implemented in order to create distinct conditions of certainty

and uncertainty regarding impending ball speed and hence temporal constraints. Based on previous

studies of movement kinematics in interception tasks, it was hypothesised that under blocked-order

conditions a close coupling between ball speed and spatiotemporal adaptations would be evident. An

earlier movement onset under higher temporal constraints was expected to be accompanied with a

-$*+03%$-)8/'%#"-,) -.*-)1*0)*7:20-/7) -%) -./)03/#"&#) -/!3%$*')#%+0-$*"+-) HB*2$/+-)/-)*'5)RSSK[)B")*+7)

B*2$/+-)RSSb[)]*<,+)/-)*'5)IJJTL5);%1/8/$()*)7"44/$/+-)-$*+03%$-)8/'%#"-,)3$%&'/)1*0)/N3/#-/7)2+7/$)

random-order conditions, with a higher and earlier occurring maximal wrist velocity (Button et al. 2002;

Daum et al. 2007), independently of the unexpected temporal constraint.I!B4D&G

67

METHODS

Participants

In order for participants to be successful under the rather demanding temporal constraints imposed

"+)-./)/N3/$"!/+-()*+7)./+#/)-%)/+02$/)-.*-)-./$/)1*0)+%)@%%$)/44/#-()"-)1*0)$/>2"$/7)-.*-)-./,).*7)

partaken in some form of ball sport (i.e., soccer, tennis, volleyball) for several years, and that in a pre-

test they could catch 14 out of 20 balls at a ball speed of 13.3 m/s. In addition, to ensure that catching

3/$4%$!*+#/)1*0)+%-)"+@2/+#/7)E,)'"!"-*-"%+0)"+)0-*+7*$7)42+#-"%+"+6)%4)-./)8"02*')0,0-/!)H0//)]*<,+)

et al. 2004), participants were required to achieve visual acuity of 0.90 on the Snellen E-chart, as well

as 0*,#2%)0-/$/%)*#2"-,)%4)KJ)0)%4)*$#)%+)-./)Y*+7%!)d%-)O-/$/%)P2--/$@,)-/0-)E*--/$,)HO-/$/%)C3-"#*')

Company, Inc., Chicago, USA). Having scanned volunteer participants on these criteria, 15 male self-

declared right handed participants (mean age: 21.5 ± 2.6 years) were selected. All participants gave

their written informed consent in the experiment, which was approved by the Ethical Committee of

the host University.

Task and apparatus

Participants were asked to stand still in a relaxed standing position with their feet parallel, arms

besides the body with the thumb of the right hand holding a switch located on the right thigh, and

head upright with gaze located straight ahead. Yellow, mid-pressured tennis balls were launched at a

distance of 8.4 m from the participant’s frontal plane by a ball-projection machine (Promatch/Mubo

B.V., Gorinchem, The Netherlands) at four different speeds (9.4 ± 0.08 m/s, 11.4 ± 0.36 m/s, 13.3 ±

J5I_)!k0)*+7)Rb5j)l)J5RT)!k0L()$/02'-"+6)"+)E*'')@"6.-)-"!/0)%4)jST)l)Z5b)!0()Z_Z)l)IK5_)!0()TIS)l)RR5J)

ms and 532 ± 5.5 ms respectively1. Small inter-trial variability for each ball speed was inevitable and was

$/@/#-/7)E,)*)#%/4&#"/+-)%4)8*$"*-"%+)E/-1//+)J5S)*+7)_5Im5)M)."6./$)E*'')03//7)$/02'-/7)"+)*)'%1/$)E*'')

@"6.-)-"!/)*+7)*)."6./$)-/!3%$*')#%+0-$*"+-5)U./)"+"-"*')./"6.-)%4)-./)E*'')!*#."+/)*+7)'*2+#.)*+6'/)1*0)

PART II

68

PART IIPART II

adjusted so that the balls arrived above the participant’s right shoulder for each of the four approach

speeds with a spatial standard deviation of not more than 11 cm. In order to avoid visual anticipation of

launching angle, and hence the ball approach speed, the ball machine was covered with black plastic that

had a small cut-out section through which the balls were released; an opto-electric device was mounted

at the exit of the ball machine to detect the time of ball release. Finally, to minimize auditory anticipation

of the moment of ball release, as well as ball speed, participants wore headphones that minimized sound

generated by the ball machine during ball release. A face shield was worn to protect the face, while not

7"0-2$E"+6)*##/00)-%)-./)42'')8"02*')&/'75)

The catching movement with the right arm was tracked with a 3D motion analysis system (Qualisys

AB, Gothenburg, Sweden) operating at 240 Hz. Eight infrared cameras were used to register the position

%4)$/@/#-"8/)!*$9/$0)-.*-)1/$/)*--*#./7)1"-.)*7./0"8/)-*3/)%+)9/,)'%#*-"%+0)%4)-./)3*$-"#"3*+-G0)*$!)

*+7).*+75)O3/#"&#*'',()-./)!*$9/$0)1/$/)3'*#/7)%+X)0.%2'7/$)H02'#20)"+-/$-2E/$#2'*$"0)%4)-./).2!/$20L()

elbow (epicondylus lateralis and medialis of the humerus), wrist (processus styloideus of radius and

ulna) and hand (Caput metacarpale I, II and V and phalanx distalis of pollux, index and digitus minimus). A

switch was attached to the participant’s right thigh in order to provide information about the initiation

of the catching movement. When the switch was released, an analogue signal (3.9 volts) was generated

that was input to the motion analysis system. A microphone was mounted on the forearm near the

participant’s wrist, and was used to record an audio signal that enabled the moment of ball-hand contact

to be derived. An additional webcam was used as a witness camera during every trial.

Procedure

Participants attempted to catch a total of 160 balls that were projected at four different ball speeds

in two conditions that differed according to presentation order. In a blocked-order condition, balls were

projected in 4 blocks of 20 trials in which the same ball speed was repeated from trial-to-trial. The order

of the blocks was randomly assigned across participants. In a random-order condition, 80 trials were

randomly ordered and delivered in 4 blocks such that each ball speed was received 20 times. By using a

1) P*'') @"6.-) -"!/0() $/02'-*+-) E*'')speeds and landing locations were evaluated in a pilot study conducted prior to the experiment. High Speed Cameras (Bassler AG, Ahrensburg, Germany) registered at 100 Hz the moment the ball left the ball machine and contacted a panel that was at 8.4 m from the ball machine (participant’s frontal plane).

I!B4D&G

69

fully randomised order, it was possible that the same ball speed could be repeated from trial-to-trial. All

participants were exposed to both conditions. Eight participants started in the blocked-order condition,

seven in the random-order condition.

Every trial followed the same procedure. Before the ball was launched, the participant looked at the

experimenter. After a signal from the experimenter (i.e., raising of the right-hand thumb), the participant

focussed his gaze on the ball machine and was aware that a ball would soon be released. Participants

were instructed to catch as many balls as possible but they were given no further explanations on the

purpose of the experiment in order to avoid conceivable anticipation due to this prior knowledge (e.g.,

the supposition that trials would arrive at the same ball speed in the blocked-order condition). Trials in

1."#.)-./)3*$-"#"3*+-)%$)/N3/$"!/+-/$)$/3%$-/7)-.*-)-./$/)1*0)*)!*:%$)7/8"*-"%+)%4)-./)+%$!*')@"6.-)

path were not examined. These trials were retaken after each block of 20 trials in the blocked-order

condition and after the 80 trials in the random-order condition.

Dependent measures and data analysis

Each trial was scored as a catch, a touch (ball-hand contact, but no catch) or a miss (no ball-hand

contact) (see Bennett et al. 1999). Successful trials (catches) were further examined by means of a

kinematic analysis completed using proprietary motion analysis software (Visual 3D v4.00.17, C-motion

Inc., Gaithersburg, MD, USA). Several kinematic variables were derived from the time-synchronised

analogue signals of the optoelectronic trigger, thigh-located switch and microphone, in combination

with the 3D-coordinates of the markers positioned on the catching arm and hand. The position data

4$%!)-./)!*$9/$0)1*0)&'-/$/7)1"-.)*)P2--/$1%$-.)'%1D3*00)&'-/$)%4)0/#%+7)$/#2$0"8/)%$7/$)*-)*)#2-D

off frequency of 10 Hz. Due to a technical problem, data from one of the participants could not be

included in the kinematical analysis.

Following on from the work of Mazyn et al. (2006), the following kinematic measures were extracted:

Y/03%+0/)-"!/)HY0UL()1."#.) "0)-./)-%-*')72$*-"%+)4$%!)-./)!%!/+-)-./)E*'')&$0-)*33/*$/7)2+-"') -./)

moment of ball-hand contact; Latency time (LT), which is the time between ball appearance and release PART II

70

PART IPART IIPART II

of the thigh-located switch; Movement time (MT), which is the time between release of the thigh-located

switch and ball-hand contact; Grasping time (GT), which is the time between maximal hand aperture

and ball-hand contact. From the momentary wrist velocity, that was calculated as the resultant of the

velocities in the /F y and)7 axes, the following variables were determined: Initial Wrist Velocity (WVini),

1."#.)"0)-./)!/*+)1$"0-)8/'%#"-,)72$"+6)-./)&$0-)RJJ)!0)*4-/$)$/'/*0/)%4)-./)-."6.D'%#*-/7)01"-#.[)Q/*9)

Wrist Velocity (PWV) during the catching action; Time To Peak Wrist Velocity (T_TO_PWV), which is

the time between movement onset and the moment of peak wrist velocity; and Time After Peak Wrist

Velocity (T_AFTER_PWV), which is the time between peak wrist velocity and ball-hand contact. The

c%/4&#"/+-)%4)0-$*"6.-+/00)Hc%OL)1*0)*'0%)/N-$*#-/7)*+7)03/#"&/0)-./)$/#-"'"+/*$"-,)%4)-./)1$"0-)3*-.5)

CoS is the total distance the wrist covers between movement onset and ball-hand contact divided by

the shortest path possible between these two points multiplied by 100 (see also Mazyn et al. 2004,

2006, 2007). We also calculated DxW, which is the linear distance between the position of the wrist at

movement onset and ball-hand contact in the anterior-posterior axis (/ axis). Peak of Hand Aperture

(PHA) was determined as the maximal linear distance between thumb and index during the unfolding

of the catch.

The number of catches, touches and misses were submitted to separate 4 ball speed (9.4, 11.4,

13.3, 15.8 m/s) ! 2 condition (blocked-order, random-order) ANOVA with repeated measures on

both factors. Intra-participant mean data from the successful trials for each kinematic measure were

calculated and submitted to separate 4 ball speed (9.4, 11.4, 13.3, 15.8 m/s) ! 2 condition (blocked-

order, random-order) ANOVA with repeated measures on both factors. Finally, in order to elucidate

the differences between caught and touched trials, additional ANOVA with repeated measures were

executed on the intra-participant mean and standard deviations of the kinematics, with levels depending

%+) -./) 024&#"/+-) +2!E/$) %4) #*-#./0) *+7) -%2#./0) 4%$) /8/$,) #%+7"-"%+) *+7) E*'') 03//75)U./) '/8/') %4)

0"6+"&#*+#/)1*0)0/-)*-)p ! 0.05. In the case of violations of the sphericity assumption, F values were

*7:20-/7)1"-.)-./)=$//+.%20/D=/"00/$)3$%#/72$/5)O"6+"&#*+-)!*"+)*+7)"+-/$*#-"%+)/44/#-0)1/$/)42$-./$)

analyzed using Newman-Keul post-hoc tests (p < 0.05).

71

I!B4D&G

RESULTS

Performance outcome

A main effect of ball speed was evident for number of catches (F2,30

= 81.804, p < 0.001), touches

(F3,42

= 81.179, p < 0.001) and misses (F1,20

= 19.158, p)n)J5JJRL5)U./$/)1/$/)+%)0"6+"&#*+-)!*"+)/44/#-0)

of condition or interaction effects for number of catches or touches. Post-hoc testing indicated that in

E%-.)-./)E'%#9/7D%$7/$)*+7)$*+7%!D%$7/$)#%+7"-"%+0()-./$/)1*0)*)0"6+"&#*+-)7/#$/*0/)"+)-./)+2!E/$)

of balls caught (p < 0.001), and a corresponding increase in number of touches as ball speed increased

from 11.4 to 13.3 m/s, and then again from 13.3 to 15.8 m/s (p < 0.001); the number of catches and

touches did not differ between the two slowest balls speeds. Participants caught almost all balls at the

lowest ball speed and only half of the balls at the highest ball speed (see Fig. 1).

Figure 1. A2165"08)$',.*,#206'F)

1*965'3)20()#"33'3)21)15').*9,)<2%%)

3$''(3) .*,) <%*64'(;*,(',) 6*0("1"*0)

dRe)20(),20(*#;*,(',)6*0("1"*0)dKe)

23) 2) $',6'0128') *.) 1*12%) 62165"08)

1,"2%3)21)1521)<2%%)3$''()20().*,)1521)

6*0("1"*0)d0)f)EGePART II

72

PART IPART IIPART II

U./$/)1*0().%1/8/$()*)0"6+"&#*+-)E*'')03//7)o)#%+7"-"%+)"+-/$*#-"%+)4%$)-./)*!%2+-)%4)E*''0)!"00/7)

(F1,17

= 9.083, p < 0.001). While there were a very small number of misses overall, there was a difference

between the conditions at the highest speed. On average 1.13 balls were missed in the random-order

condition compared to 0.33 balls missed in the blocked-order condition (p < 0.001).

Kinematics

Table 1 shows the means and standard deviations of the kinematic variables as a function of ball

speed and condition, as well the resulting interaction effects. For the purpose of brevity, main effects of

ball speed and condition are described in the main body text where appropriate.

There was a main effect of ball speed for RsT (F3,39

= 16,101.327, p < 0.001), but no main effect of

condition or an interaction effect. Post-hoc testing indicated that RsT decreased for each increase in ball

speed (p n)J5JJRL5)U./$/)1/$/().%1/8/$()0"6+"&#*+-)"+-/$*#-"%+)/44/#-0)4%$)]U)HF3,39

= 6.307, p < 0.01)

and LT (F3,39

= 15.198, p < 0.001). MT (p < 0.001) and LT (p < 0.001) were reduced in both conditions

as ball speed increased from 11.4 to 13.3 m/s and then to 15.8 m/s. Importantly, though, at the lowest

ball speed, LT was shorter (p < 0.001) and MT longer (p < 0.001) when catching in the random-order

condition than in the blocked-order condition (see Fig. 2).

73

I!B4D&G

Figure 2. >+',+"'-)*.)15')1'#$*,2%)31,9619,')*.)15')62165"08)#*+'#'01)21)15').*9,)<2%%)3$''(3).*,)<%*64'(;

*,(',)6*0("1"*0)20(),20(*#;*,(',)6*0("1"*0)d0)f)EIe=)g',*;$*"01)"3)3'1)21)15')#*#'01)*.)#*+'#'01)*03'1=)

V@)"3)"0)<%264F)8,':)352('3),'h'61)Q@=)@i^]@?KiUBT)"06%9('3)H@

PART II

74

PART IPART IIPART II

Table 1. Q'203) 20() 3120(2,() ('+"21"*03) d!`e) *.) 4"0'#21"62%) +2,"2<%'3) .*,) 15') .*9,) <2%%) 3$''(3) 90(',)

15'))<%*64'(;)20(),20(*#;*,(',)6*0("1"*0=)!121"31"62%))"01',261"*0)'..'613)*.)<2%%)3$''()j)6*0("1"*0).*,)'+',:)

('$'0('01)+2,"2<%')d0)f)EIe

75

I!B4D&G

Table 1 (continued).)Q'203)20()3120(2,()('+"21"*03)d!`e)*.)4"0'#21"62%)+2,"2<%'3).*,)15').*9,)<2%%)

3$''(3) 90(',) 15') ) <%*64'(;) 20() ,20(*#;*,(',) 6*0("1"*0=) !121"31"62%) ) "01',261"*0) '..'613) *.) <2%%) 3$''() j)

6*0("1"*0).*,)'+',:)('$'0('01)+2,"2<%')d0)f)EIe

a"62$/)_*)0.%10)-./)"+-/$D3*$-"#"3*+-)!/*+)1$"0-)8/'%#"-,)3$%&'/0)*-)/*#.)E*'')03//7)*+7)#%+7"-"%+5)

U./)"+-$*D3*$-"#"3*+-)!/*+)1$"0-)8/'%#"-,)3$%&'/0)%4)-.$//)$/3$/0/+-*-"8/)"+7"8"72*'0)*$/)3$/0/+-/7)"+)

a"65)_ED75) A-)#*+)E/)0//+)-.*-() 4$%!)!%8/!/+-) "+"-"*-"%+)%+()-./)1$"0-)8/'%#"-,)3$%&'/0)1/$/)7"44/$/+-)

between ball speeds in the blocked-order condition (left panel), while they were more similar between

E*'') 03//70) 4%$) -./) &$0-) RJJ)!0) "+) -./) $*+7%!D%$7/$) #%+7"-"%+) H$"6.-) 3*+/'L5)U."0)1*0) $/@/#-/7) "+)

*)0"6+"&#*+-) "+-/$*#-"%+)/44/#-) 4%$)fi"+") HF3,39

= 20.81, p < 0.001). Initial wrist velocity differed with PART II

76

PART IPART IIPART II

each ball speed in the blocked-order condition whereas in the random-order condition only the initial

wrist velocity for the lowest ball speed was different from the other three ball speeds (p < 0.005).

U./)"+-/$*#-"%+)/44/#-)4%$)Qfi)*'0%)*33$%*#./7)#%+8/+-"%+*')'/8/'0)%4)0"6+"&#*+#/)HF2,22

= 3.396, p =

0.06). PWV tended to increase with each increase in ball speed for both conditions (F3,39

= 176.807,

p < 0.001) but this amplitude scaling was more evident when trials were received in blocked-order.

M)0"6+"&#*+-)E*'')03//7)o)#%+7"-"%+)"+-/$*#-"%+)1*0)+%-/7)4%$)UpUCpQfi)HF2,21

= 14.740, p < 0.001)

and T_AFTER_PWV (F3,39

= 33.126, p < 0.001). Post-hoc testing indicated that T_TO_PWV did not

change over ball speed for the random-order condition, whereas in the blocked-order condition there

was a difference between the two lowest ball speeds (p < 0.001) as well as between the two highest

ball speeds (p < 0.001; Fig. 2 and 3), showing evidence of time scaling. T_AFTER_PWV was reduced for

both conditions with increasing ball speed (p < 0.001), but was longer in the random-order condition

than the blocked-order condition at the two lowest ball speeds (p < 0.001) and shorter at the highest

ball peed (p < 0.001).

U./$/)1*0)*)0"6+"&#*+-)"+-/$*#-"%+)/44/#-)4%$)#%/4&#"/+-)%4)0-$*"6.-+/00)HF3.39

= 8.681, p < 0.001).

Post-hoc tests revealed that for both conditions the two higher ball speeds (13.3 and 15.8 m/s) resulted

in a more rectilinear trajectory as the wrist was moved to the place of contact (p < 0.001). There

was, however, a difference between conditions at the lowest ball speed, with a higher CoS exhibited

in the random-order condition than the blocked-order condition (p < 0.001). The effect of ball speed

*33$%*#./7)0"6+"&#*+#/)4%$)dNf)HF2,20

= 3.590, p = 0.06) and tended to be lower at the highest speed

as compared to the lower ball speeds. For PHA there was a main effect of ball speed (F3,39

= 27.04, p <

0.001) and condition (F1,13

= 4.477, p = 0.05). PHA increased as a function of each increase in ball speed

and was on average 0.2 cm greater for the blocked-order condition as compared to the random-order

#%+7"-"%+5)U./$/)1/$/)+%)0"6+"&#*+-)/44/#-0)%4)E*'')03//7)%$)#%+7"-"%+)4%$)6$*03"+6)-"!/)H=UL5)=$*03)

initiation occurred at a constant time of approximately 60 ms before ball-hand contact.

77

I!B4D&G

Figure 3. B,"31) +'%*6"1:)

$,*&%'3) .*,) <%*64'(;*,(',)

d%'.1) $20'%e) 20() ,20(*#;

*,(',) d,"851) $20'%e)

6*0("1"*03) 21) 15') .*9,)

<2%%) 3$''(3=) Q'20) -,"31)

+'%*6"1"'3)*.)2%%)$2,1"6"$2013)

d0)f) EIe) 2,') ,'$,'3'01'()

(ae) 23) -'%%) 23) 15,'')

"0("+"(92%) $2,1"6"$2013) ^U)

(beF)OR)dce)20()KR)dde=)U%93)

3:#<*%3) ,'$,'3'01) U'24)

B,"31)T'%*6"1:PART II

78

PART IPART IIPART II

For the highest ball speed, 2 outcome (catch, touch) ! 2 condition (blocked-order, random-order)

ANOVA with repeated measures on both factors were calculated on the intra-participant mean and

0-*+7*$7)7/8"*-"%+0)%4)-./)9"+/!*-"#0()0"+#/)4%$)-.*-)E*'')03//7)-./$/)1*0)*)024&#"/+-)*!%2+-)%4)#*-#./0)

*+7)-%2#./0)4%$)/*#.)3*$-"#"3*+-5)W%)0"6+"&#*+-)/44/#-0)1/$/)4%2+7)4%$)Y0U()E2-)-./) "+-$*D3*$-"#"3*+-)

standard deviation of RsT was larger (±2 ms) for touches than for catches in both conditions (F1,13

=

5.263, p)n)J5JbL5);%1/8/$()"+#'27"+6)-%2#./0)"+)-./)*+*',0"0)$/02'-/7)"+)*)0"6+"&#*+-)/44/#-)%4)#%+7"-"%+)

for LT (F1,13

= 6.483, p < 0.05) MT (F1,13

= 5.283, p < 0.05) and WVini (F1,13

= 13.215, p < 0.005). LT

was on average 9 ms longer and MT 7 ms shorter for random-order catching than for blocked-order

#*-#."+6()1."'/)"+"-"*')1$"0-)8/'%#"-,)1*0)lJ5__)!k0)'%1/$5)BU)*33$%*#./7)0"6+"&#*+#/)4%$)-./)%2-#%!/)

! condition interaction (F1,13

= 3.688, p = 0.08): in the blocked-order condition, LT was on average

between 201 and 202 ms for both catches and touches, whereas movement started on average later

(215 ms) when the ball was touched than when caught successfully (207.5 ms) in the random-order

#%+7"-"%+5)U./$/)1*0)*)0"6+"&#*+-)"+-/$*#-"%+)4%$)-./)"+-$*D3*$-"#"3*+-)8*$"*E"'"-,)%4)UpUCpQfi)HF1,13

=

4.718, p < 0.05): whereas the standard deviation of T_TO_PWV was the same for the random-order

condition whether the ball was caught or touched (±28 ms), variability was greater for touches (78 ms)

-.*+)4%$)#*-#./0)HRj)!0L)"+)-./)E'%#9/7D%$7/$)#%+7"-"%+5)W%)%-./$)0"6+"&#*+-)/44/#-0)1/$/)8"0"E'/)4%$)-./)

kinematic variables and their standard deviations.

79

I!B4D&G

DISCUSSION

The objective of this study was to explore the effect of advance knowledge regarding temporal

constraints of a one-handed catching task on performance outcome and movement kinematics. By

presenting balls to be caught at one of four different ball speeds in either blocked-order or random-

order, we aimed to determine if participants’ certainty of expectation regarding the temporal

#%+0-$*"+-0)%4)E*'')-$*:/#-%$,)4*#"'"-*-/7)*)!%7"&#*-"%+)-%)-./)!%-%$)$/03%+0/)*+7)./'3/7)-%)!*"+-*"+)

successful performance. The blocked-order condition was expected to provide knowledge gathered

72$"+6)3$/8"%20)-$"*'0)$/6*$7"+6)-./)23#%!"+6)E*'')03//7()./+#/)$/02'-"+6)"+)/4&#"/+-)*7*3-*-"%+0)-%)-./)

temporal constraints such as an earlier movement onset and a higher maximal wrist velocity under

higher temporal constraints. Under conditions of uncertainty about the temporal constraints (random-

order ball speed), it was expected that the participants would attempt to minimize errors and hence

exhibit a generalized response in which they move their hand with a high and early occurring peak

wrist velocity. In this respect, movement kinematics in the random-order condition would be largely

"+7/3/+7/+-)%4)-./)03/#"&#)-/!3%$*')#%+0-$*"+-)%4)/*#.)-$"*'5

Consistent with previous work (Laurent et al. 1994; Bennett et al. 1999; Mazyn et al. 2006), it was

found that catching performance decreased with increasing ball speed and hence increasing temporal

constraints. The decrease in number of catches was accompanied by an increase in number of touches

H0//)a"65)RL()"+7"#*-"+6)-.*-)-./)&+/)03*-"%-/!3%$*')#%+-$%')%4)-./)#*-#."+6)*#-"%+)$/>2"$/7)-%)02##/0042'',)

6$*03)-./)E*''()1*0)*44/#-/7)HP/++/--)/-)*'5)RSSSL5)M'-.%26.)%+',)Rm)%4)-./)E*''0)1/$/)-%-*'',)!"00/7()-./$/)

was a larger number of misses when attempting to catch balls projected with the highest speed in the

$*+7%!D%$7/$)#%+7"-"%+)#%!3*$/7)-%)-./)E'%#9/7D%$7/$)#%+7"-"%+5)U."0)&+7"+6)!"6.-)"+7"#*-/)*)8/$,)

marginal advantage in terms of outcome performance in blocked-order conditions due to an advance

knowledge effect but overall there was little difference between blocked-order and random-order

catching performance.

Analysis of successful catches indicated that there was a change in kinematics as a function of

temporal constraints (see Table 1 and Fig. 2, see also Laurent et al. 1994; Mazyn et al. 2006). In both the PART II

80

PART IPART IIPART II

blocked-order and random-order conditions, the increase in ball speed resulted in a reduced response

time, latency time, movement time, higher peak wrist velocity, a more rectilinear movement trajectory

*+7)*)."6./$)3/*9)%4).*+7)*3/$-2$/5)U./)%E0/$8/7)*7*3-*-"%+0)"+)]U)*+7)Q/*9f$i/')#%+&$!)#*-#./$0G)

ability to meet the time-accuracy demands of the task at hand (Tresilian et al. 2009). Perhaps surprisingly,

DxW was only marginally (p = 0.06) different between ball speed-conditions. The backward shift of

the place of ball-hand contact under increasing temporal constraints that has previously been reported

(Laurent et al. 1994; Mazyn et al. 2006) was much smaller in the current study and only evident at the

highest ball speed-condition. This unexpected result, greater differences could be expected especially

in the blocked-order condition, might be explained by small methodological differences between these

studies. For example, visual anticipation before ball release could not be avoided in the study of Mazyn

et al. (2006). This could account for the greater LT and smaller MT in the current experiment, because

participants might have waited longer in order to acquire more visual information, followed by a reduced

movement execution.

Despite not permitting outcome performance to be maintained (see above), the adaptations to the

spatio-temporal control of the catching hand were functional and resulted in the grasp being initiated at

*)#%+0-*+-)-"!/)%4)TJ)!0)E/4%$/)E*''D.*+7)#%+-*#-)Ha"65)IL5)O"!"'*$)&+7"+60)%4)*)#%+0-*+-)-"!/D-%D#%+-*#-)

strategy for the timing of the grasp in catching have been reported in many other studies (Lacquaniti and

Maioli 1989; Savelsbergh et al. 1991, 1993; Laurent et al. 1994; Button et al. 2002; Mazyn et al. 2006).

;%1/8/$() -./$/)1*0) *'0%) *) 6/+/$*') -/+7/+#,) 4%$) *78*+#/) 9+%1'/76/)%4)E*'') 03//7) -%) "+@2/+#/)

movement kinematics at the lower balls speeds. The catching movement was initiated earlier after ball

release (i.e., reduced LT) in the random-order condition and was accompanied by a greater magnitude

of peak wrist velocity that occurred at a similarly earlier time of 160-170 ms after movement onset; for

evidence of a comparable adaptation in wrist velocity in the face of an unexpected perturbation, see

P2--%+)/-)*'5)HIJJJ()IJJIL5)M0)0.%1+)"+)a"65)_()-./)"+"-"*')1$"0-)8/'%#"-,)H&$0-)RJJ)!0L)1*0)#'/*$',)*7:20-/7)

to ball speed in the blocked-order condition (left panel), whereas some overlap in the initial part of

the wrist velocity was visible in the random-order condition (right panel, see also van Donkelaar et al.

1992). The magnitude of peak wrist velocity was scaled to ball speed in both conditions, although to a

81

I!B4D&G

lesser extent for the random-order condition. Nevertheless, whereas the timing of peak wrist velocity

in the blocked-order condition co-varied with ball speed (Fig. 3, left panel), no such time scaling of wrist

velocity was evident in the random-order condition (Fig. 3, right panel). These differences in wrist velocity

3$%&'/)1/$/)!%$/)/8"7/+-)4%$)0%!/)3*$-"#"3*+-0)Ha"65)_E(#L)-.*+)4%$)%-./$0)Ha"65)_7L5);*8"+6)"+"-"*-/7)

the movement earlier and with a greater magnitude of initial wrist velocity, participants then moved

with a less rectilinear hand path in the random-order condition than the blocked-order condition at

the lowest ball speed. In combination, these adaptations resulted in a longer movement time, which is

consistent with a mode of control in which participants use a larger temporal window to negotiate the

unexpected temporal constraint on-line. Importantly, however, it was only possible to use this mode of

control when the temporal constraints were not too severe.

In an attempt to elucidate the possible reasons for failures, kinematics of caught trials were compared

to touched trials. This was only possible at the highest ball speed, since for that ball speed-condition

024&#"/+-)-$"*'0)1/$/)/8"7/+-)-%):20-"4,)*+)*+*',0"05)Y/03%+0/)-"!/)1*0)!%$/)8*$"*E'/)1"-."+)3*$-"#"3*+-0)

for trials that were touched as compared to catches, indicating a more stable timing in successful trials,

even though the differences were very small (± 2 ms). Inclusion of the touched trials with the caught

-$"*'0)$/02'-/7)"+)*)0"6+"&#*+-',)'%+6/$)BU)*+7)0.%$-/$)]U)4%$)$*+7%!D%$7/$)#*-#."+6)*0)#%!3*$/7)-%)

blocked-order catching. At this highest ball speed, initial wrist velocity was higher for blocked-order

catching than for random-order catching. It seems that advanced knowledge of ball speed resulted in

*)."6./$)"+"-"*')1$"0-)8/'%#"-,)E/#*20/)*)."6.)E*'')03//7)1*0)/N3/#-/75)U./$/)1*0)*'0%)*)+/*$)0"6+"&#*+-)

interaction for LT: in random-order trials that were touched, movement onset was delayed as compared

to blocked-order and successful random-order catching. The absence of advance information of ball

speed might have resulted in an unbalanced timing with too much time for movement preparation and

too little for movement execution. For blocked-order catching, failures were characterized by a greater

variability to reach the peak of wrist velocity. However, while explanations for failure at that ball speed

might be speculative, catching performance remained equal for both conditions.

M'-.%26.)*78*+#/)9+%1'/76/)%4)E*'')03//7)7"7)+%-)$/02'-)"+)*)0"6+"&#*+-)6$/*-/$)*!%2+-)%4)E*''0)

caught in this experiment, it can be argued that participants use of different movement planning and PART II

82

PART IPART IIPART II

#%+-$%') 0-$*-/6"/0)1/$/) E/0-) &-) 2+7/$) -./) 6"8/+) #"$#2!0-*+#/05) A+) -./) E'%#9/7D%$7/$) #%+7"-"%+() -./)

advance knowledge of ball speed permitted a movement strategy closely adapted on a trial-by-trial

basis to the temporal constraints. For instance, when participants knew that a slow ball was coming,

they delayed movement onset and then adapted the subsequent movement to the remaining time

%4)@"6.-5)A+)-./)$*+7%!D%$7/$)#%+7"-"%+().%1/8/$()"-)1%2'7)0//!)-.*-)3*$-"#"3*+-0)3$%72#/7)*+)"+"-"*')

response that had more ('.29%1 time and velocity characteristics. Such an approach has been reported

previously in several other tasks and is suggested to be adaptive in the sense that it gives participants

"+#$/*0/7)%33%$-2+"-,)-%)$/03%+7)-%)*+)2+#/$-*"+)0"-2*-"%+5)A+7//7()-./$/)1%2'7).*8/)E//+)#'/*$)E/+/&-)

to respond with an early movement of high magnitude velocity in the random-order condition because

E*''0)3$%:/#-/7)*-)-./)."6./0-)03//70)1%2'7).*8/)E//+)8/$,)7"4&#2'-)-%)#*-#.).*7)3*$-"#"3*+-0)*7%3-/7)

similar movement kinematics to those used for the slower ball speeds in the blocked-order condition.

The cost associated with using a initial ('.29%1 response would in fact be quite low because participants

could continue with this response if the ball speed was high, while they could modify their movement

kinematics online if the ball speed actually turned out to be lower than initially planned for. In contrast

to the blocked-order condition, where adaptations to ball speed could be prepared well in advance,

"-)1*0)%+',)*-) -./)8/$,)!%!/+-)%4)E*'') $/'/*0/)H"5/5()1./+)-./)&$0-)8"02*') "+4%$!*-"%+)1*0)*8*"'*E'/L)

-.*-)3*$-"#"3*+-0)"+)-./)$*+7%!D%$7/$)#%+7"-"%+)#%2'7)0-*$-)-%)"+#%$3%$*-/)*7*3-*-"%+0)-%)-./)03/#"&#)

ball speed in their movement plan and subsequent control. Before that moment of ball release, the

uncertainty of ball speed could only lead to a default preparation, which resulted in the observed #*,')

('.29%1)!%-%$)*+01/$5)W%-/)-.*-)-."0)7"44/$/+-)!%8/!/+-)0-$*-/6,)0-"'')$/02'-/7)"+)*+)/>2*'',)/4&#"/+-)

catching performance that provides additional evidence of the capability of the perceptuo-motor system

to adapt its actions depending on the imposed task constraints (van der Kamp et al. 1997; Mazyn et al.

2007).

c'/*$',()-./+()-./)&+7"+60)"+)-./)#2$$/+-)0-27,)%4)7"44/$/+#/0)E/-1//+)#*-#."+6)2+7/$)E'%#9/7D%$7/$)

and random-order temporal constraints suggest that participants exerted some cognitive control over

-./"$)!%8/!/+-)/N/#2-"%+5)U."0)"+-/$3$/-*-"%+)"0)7"4&#2'-)-%)$/#%+#"'/)1"-.)*+)/N#'20"8/)%+D'"+/)#%+-$%')

0-$*-/6,) "+)1."#.) -./) "+@2/+#/)%4) #%6+"-"8/)%3/$*-"%+0) 02#.)*0)/N3/#-*-"%+)*+7)3$"%$) 9+%1'/76/) "0)

$/:/#-/7)H]"#.*/'0)IJJJ[)]"#.*/'0)/-)*'5)IJJRL5);%1/8/$()1/)7%)+%-)"+-/$3$/-)-./0/)&+7"+60)-%)0266/0-)

83

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that the human system is not able to control most of the daily-life activities by means of direct feedback

loops based on on-line visual information. Instead, we agree with the suggestion that some kind of

internal representation might aid at least a part of movement control (Norman 2002; Zago et al. 2009;

Nitsch 2009) and that this is even more pronounced in so-called 900219,2% (Jensen et al. 1989) sport

situations that impose severe temporal constraints (Regan 1997).

For future research that is intended to be relevant for real life situations in which there is trial-

to-trial variability in ball speed due to human factors (Ranganathan and Carlton 2007; Werner et al.

2008; Moras et al. 2008), the results of the current study highlight the importance of randomizing ball

03//705)M78*+#/)9+%1'/76/)E*0/7)%+)3$/#/7"+6)-$"*'0).*0)*)0-$%+6)"+@2/+#/)%+)-./)#%+-$%')%4)#*-#."+6)

movement that is not evident in outcome performance. While it remains unclear what contribution to

the observed differences in movement kinematics is made by recent experience of previous trials and/

or the expression of explicit knowledge of upcoming trials (de Lussanet et al. 2002; Song and Nakayama

IJJZL()"-)1"'')E/)"+-/$/0-"+6)-%)/N*!"+/)"+)42-2$/)1%$9)-./)"+@2/+#/)%4)03*-"*')2+#/$-*"+-,)%+)"+-/$#/3-"8/)

behaviour, in order to examine human behaviour in representative designs (Araujo et al. 2007). Only

-./+)"-)1"'')E/)3%00"E'/)-%)6/+/$*'"</)/!3"$"#*')&+7"+60)-%)*)$/*')'"4/)0"-2*-"%+5)

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CONCLUSION

U./)#2$$/+-)/N3/$"!/+-)0.%10)-.*-)"!3'"#"-)*78*+#/)9+%1'/76/)%4)E*'')03//7).*7)*+)"+@2/+#/)%+)

movement kinematics, although catching performance remained the same. Trials that were presented

in blocks of the same ball speed led to a better scaling of movement kinematics based on expectancy

4$%!)3$/8"%20)-$"*'05)U./$/4%$/()-./)"+@2/+#/)%4)*78*+#/)9+%1'/76/)0.%2'7)E/)*#9+%1'/76/7)"+)42-2$/)

experimental designs.

ACKNOWLEDGEMENTS

The authors are grateful to Ann Van Landeghem for helping with data collection.

85

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Savelsbergh GJP, Whiting HTA, Bootsma RJ (1991) Grasping tau. O*9,02%)*.)?/$',"#'012%)U3:65*%*8:W)

[9#20)U',6'$1"*0)20()U',.*,#206'F)EJ, 315-322

Savelsbergh GJP, Whiting HTA, Pijpers JR, Van Santvoord AAM (1993) The visual guidance of catching.

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Werner SL, Suri M, Guido JA, Meister K, Jones DG (2008) Relationships between ball velocity and

throwing mechanics in collegiate baseball pitchers. O*9,02%)*.)!5*9%(',)20()?%<*-)!9,8',:F)EJF 905-908

Zago M, Bosco G, Maffei V, Iosa M, Ivanenko YP, Lacquaniti F (2004) Internal models of target

motion: expected dynamics overrides measured kinematics in timing manual interceptions. O*9,02%)*.)

Y'9,*$5:3"*%*8:F)LE, 1620-1634

Zago M, McIntyre J, Senot P, Lacquaniti F (2009) Visuo-motor coordination and internal models for

object interception. ?/$',"#'012%)R,2"0)K'3'2,65F)ELC, 571-604

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[ABSTRACT] U."0)0-27,)/N*!"+/7).%1)/N3'"#"-)*78*+#/)9+%1'/76/)!"6.-)"+@2/+#/)adaptive behaviour to visual occlusions. Catching performance and kinematics of good ball catchers were compared between no, early and late occlusion trials. Discrete visual occlusions of 400 ms, occurring early or late in the ball’s approach trajectory, were randomly interspersed between no occlusion trials. In one condition, the presence and type of occlusion were announced a priori (expected), whereas in another condition no such information was provided (unexpected). Expectation of occlusion resulted in an adapted limb transport and increased grasping time, whereas in the unexpected condition a higher peak of wrist velocity was evident for all occlusion conditions. The observed different adaptations cannot be explained by trial-by-trial adaptations alone *+7)"+0-/*7)3$%8"7/)/8"7/+#/)4%$)-./)"+@2/+#/)%4)/N3'"#"-)*78*+#/)9+%1'/76/)"+)-./)motor response of interceptive actions.

[KEYWORDS] Explicit advance knowledge; Interceptive actions; Visual occlusion; Adaptations; Kinematics

BASED ON: Tijtgat P, Bennett SJ, Savelsbergh GJP, De Clercq D, Lenoir M. (2011) U%)9+%1)%$)+%-) -%)9+%1X) "+@2/+#/)%4)/N3'"#"-)*78*+#/)9+%1'/76/)%4)%##'20"%+)%+)interceptive actions. ?/$',"#'012%)R,2"0)K'3'2,65F)CEI, 483-490

STUDY 2:

TO KNOW OR NOT TO KNOW: INFLUENCE

OF EXPLICIT ADVANCE KNOWLEDGE OF

OCCLUSION ON INTERCEPTIVE ACTIONS

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I!B4D&<X&&!E&L;E]&E^&;E!&!E&L;E]X&G;?CB9;A9&E?&9k6CGAG!&@4i@;A9&L;E]C94:9&E?&EAACBIGE;&E;&G;!9^A96!Gi9&@A!GE;I&

INTRODUCTION

The human perceptuo-motor system has been shown to adapt to information-based perturbations

in a variety of tasks, including repetitive (Woodworth 1899; Vince 1948) and discrete aiming tasks (Keele

and Posner 1968; Carlton 1981; Moore 1984; Elliott 1988, Elliott et al. 1995), grasping (Wing et al. 1986;

Winges et al. 2003; Fukui and Inui 2006), catching (Whiting et al. 1970, 1973, 1974; Sharp and Whiting

1974, 1975; Lamb and Burwitz 1988; Lacquaniti and Maioli 1989; Mazyn et al. 2007a, Dessing et al. 2009)

and hitting (Marinovic et al. 2009; van Soest et al. 2010). Imposing such perturbations in experimental

0/--"+60)"+@2/+#/0)4*#-%$0)02#.)*0)!%8/!/+-)3$/3*$*-"%+()*0)1/'')*0)2+7/$',"+6)#%+-$%')3$%#/00/0)-.*-)

are responsible for adaptations in kinematics as the movement unfolds (Elliott and Lee 1995; van der

Kamp et al. 1997; Schenk et al. 2004).

However, while it is clear that the availability of sensory information (e.g., full vision vs. occluded vision)

72$"+6)*)-$"*')"+@2/+#/0)!%-%$)E/.*8"%2$()\/'*<+"9)/-)*'5)HRSj_L)0.%1/7)-.*-)/N3/#-*+#,)$/6*$7"+6)-./)

upcoming sensory information is an important source of advance information. Zelaznik et al. found that

when trials are received in blocked order and hence there is a clear expectation regarding the sensory

information, aiming movements under a full vision condition were performed with a higher spatial

accuracy compared to a visual occlusion condition. However, this difference decreased when trials were

received in random order. The implication is that participants were able to use advance knowledge to

3'*+)-%)-*9/)*78*+-*6/)%4)8"0"%+)1./+)*8*"'*E'/5)O2E0/>2/+-',()"-)1*0)#%+&$!/7)-.*-)3*$-"#"3*+-0)*'0%)

adopt different movement strategies depending on their advance knowledge. For instance, movement

kinematics are consistent with an optimized use of visual feedback when an occlusion is expected,

compared to a default strategy when occlusion and no occlusion of vision are equally likely (Jakobson

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*+7)=%%7*'/)RSSR[)`.*+)/-)*'5)IJJI[);*+0/+)/-)*'5)IJJTL5)W/2$*')/8"7/+#/)4%$)-./)"+@2/+#/)%4)*78*+#/)

knowledge has been shown in motor learning (Willingham et al. 2002). Being explicitly aware of a

repeating sequence activates additional brain areas in the posterior parietal, superior parietal and dorsal

prefrontal cortex.

A somewhat different interpretation of differences between movement kinematics and outcome

when trials are performed in blocked compared to random order is necessary if one suggests that the

visuomotor system is cognitively impenetrable (Song and Nakayama 2007; Whitwell et al. 2008). As an

alternative, these authors attributed differences between blocked-order and random-order reaching

and grasping to trial-by-trial adaptations. In a catching task, Dessing et al. (2009) showed that early

%##'20"%+)H"5/5()8"0"%+)%##'27/7)4%$)*33$%N"!*-/',)-./)"+"-"*')-."$7)%4)@"6.-)-"!/L)%+',).*7)*+)/44/#-)1./+)

trials were presented in random order. The lack of effect on movement kinematics when trials were

presented in blocked order was suggested to result from trial-by-trial adaptations in the visuomotor

gain rather than velocity gain. In other words, because participants tried to catch the ball, they were able

to adapt visuomotor gain after the previous trial(s), which proved appropriate for the successive trial(s).

While not intending to refute the possibility of trial-by-trial adaptations in the aforementioned work,

it is important to consider that trials performed in blocked-order also permit the expression of implicit

advance knowledge regarding the upcoming availability of information (Tijtgat et al. 2010). The present

study, therefore, compared trials received only in random order, either with or without explicit advance

knowledge (see Button et al. 2002 for a comparable design). In this way, the study was designed to

7/-/$!"+/)-./)"+@2/+#/)%4)/N3'"#"-)*78*+#/)9+%1'/76/)1./+)-./)3%00"E"'"-,)%4)-$"*'DE,D-$"*')*7*3-*-"%+0)

was minimized. It was hypothesised that providing explicit advance knowledge regarding an upcoming

visual occlusion (i.e., early or late) would enable participants to prepare a response optimized to the

*8*"'*E'/)"+4%$!*-"%+5)O3/#"&#*'',()"-)1*0)/N3/#-/7)-.*-)4%$)-./)-$*+03%$-)3.*0/)%4)#*-#."+6()3*$-"#"3*+-0)

would respond with an earlier movement onset, in combination with an earlier and retreated wrist

displacement (Button et al. 2002; Mazyn et al. 2007a). In the grasping phase, a greater peak hand aperture

was expected as this increases the safety margin and thereby the likelihood of making a successful catch.

However, no change in the timing of the grasp was predicted as this has previously been shown to be PART II

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robust against visual occlusion (Mazyn et al. 2007a). In the absence of explicit advance knowledge, it was

hypothesised that participants would respond initially with a default control strategy irrespective of the

presence and duration of visual occlusion (Jakobson and Goodale 1991; Khan et al. 2002; Hansen et al.

2006; Mazyn et al. 2007a).

METHODS

Participants

Twenty male, self-declared right-handed participants (mean age: 22.5 ± 2.2 years) with normal

or corrected-to-normal vision gave their written informed consent for the experiment, which was

approved by the Ethical Committee of the host University. They had experience in some form of ball

sport (i.e., soccer, basketball and volleyball) and obtained a catching score of at least 17 out of 20 balls

in a pretest (ball speed: 10.62 m/s).

Task and apparatus

Before each catching trial, participants were asked to stand still in a relaxed position with their

feet parallel and the thumb of the right hand holding a switch located on the right thigh. Yellow, mid-

pressured tennis balls were launched at a distance of 10 m from the participant’s frontal plane by a

ball-projection machine (Promatch/Mubo B.V., Gorinchem, The Netherlands) with an average ball speed

%4)RJ5TI)l)J5RI)!k0()$/02'-"+6)"+)*+)*8/$*6/)E*'')@"6.-)-"!/)%4)SKI)l)RR)!0)-%)-./)3*$-"#"3*+-G0)4$%+-*')

plane. The initial height of the ball machine and launch angle was adjusted so that the balls arrived above

the participant’s right shoulder with a spatial standard deviation of no more than 13 cm. An optoelectric

device was mounted at the exit of the ball machine to detect the time of ball release. To minimize

auditory anticipation of the moment of ball release, participants listened to instrumental music played

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I!B4D&<

through headphones.

Visual occlusions were achieved with a pair of PLATO liquid-crystal occlusion goggles (Translucent

Technologies, Inc., Toronto, Ontario, Canada). The goggles were interfaced with a PC that regulated the

duration of the transparent and opaque states of the lenses. For early visual occlusion trials, the goggles

1/$/)%3/+)4%$)-./)&$0-)IJJ)!0)*4-/$)E*'')$/'/*0/()-./+)#'%0/7)4%$)KJJ)!0)*+7)&+*'',)%3/+)*6*"+)2+-"')-./)

+/N-)-$"*'5)a%$)'*-/)8"02*')%##'20"%+)-$"*'0()-./)6%66'/0)1/$/)%3/+)4%$)-./)&$0-)TJJ)!0)*+7)-./+)#'%0/7)4%$)

-./)$/!*"+7/$)%4)E*'')@"6.-)H"5/5()*33$%N"!*-/',)_bJ)!0)7/3/+7"+6)%+)-./)/N*#-)'%#*-"%+)%4)-./)E*''D.*+7)

contact). The goggles were returned to the open state between each trial. The goggles stayed open for

-./)&$0-)RJ)-$"*'0)*+7)-./)"+-/$03/$0/7)-$"*'0)1"-.%2-)%##'20"%+5)U./)#*-#."+6)!%8/!/+-)1"-.)-./)$"6.-)

arm was tracked with a 3D motion analysis system (Qualisys AB, Gothenburg, Sweden) operating at 240

;<5)g"6.-)"+4$*$/7)#*!/$*0)1/$/)20/7)-%)$/6"0-/$)-./)3%0"-"%+)%4)$/@/#-"8/)!*$9/$0)-.*-)1/$/)*--*#./7)

with adhesive tape on the following key locations: shoulder (sulcus intertubercularis of the humerus),

elbow (epicondylus lateralis and medialis of the humerus), wrist (processus styloideus of radius and

ulna) and hand (phalanx distalis of index and digitus minimus). The switch attached to the lateral side

of the participant’s right thigh was pressed with the thumb of the catching hand in preparation of each

trial. The release of the switch generated an analogue signal that provided information of the initiation

of the catching movement. A microphone was mounted on the forearm near the participant’s wrist

and was used to record an audio signal that enabled the moment of ball-hand contact to be derived1.

Experimental design and procedure

U./)/N3/$"!/+-*')7/0"6+)#%+0"0-/7)%4)-1%)3.*0/0)-.*-)1/$/)$/#/"8/7)"+)&N/7)%$7/$5)U./)&$0-)3.*0/)

comprised of blocks of trials in which participants were given advance knowledge about the availability

%4)8"02*')"+4%$!*-"%+)72$"+6)E*'')@"6.-)H/N3/#-/7)#%+7"-"%+L5)Q*$-"#"3*+-0)1/$/)6"8/+)*)1$"--/+)"+0-$2#-"%+)

from an experimenter before each trial on the type of occlusion that could be expected: no occlusion

(no), an early occlusion (early) or a late occlusion (late). In the second phase, no explicit advance

knowledge was provided (unexpected condition), leaving participants to respond to an occlusion as PART II

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and when it occurred. Both experimental phases comprised of familiarisation trials followed by test

trials. During familiarisation, participants were required to perform the catching task under randomly

assigned early or late visual occlusions until a criterion of 7 successful catches out of 10 was achieved

4%$)/*#.)%##'20"%+5)U."0)#$"-/$"%+)1*0)20/7)-%)/+02$/)-.*-)/*#.)3*$-"#"3*+-)1*0)024&#"/+-',)4*!"'"*$"</7)

to the experimental condition and was reached at on average 46 trials in the advance knowledge

phase and 26 trials in the phase without advance knowledge. Participants then completed 10 trials

with no occlusion, followed by 55 no occlusion trials with 10 early and 10 late occlusion trials randomly

interleaved (Y = 85 test trials); for a similar design see Button et al. (2002).

Apart from differences in prior instruction (i.e., advance knowledge or no advance knowledge)

between the two test phases, every trial followed the same procedure. Before the ball was launched,

the participant looked at the experimenter. After a signal from the experimenter (i.e., raising of the

right-hand thumb), the participant focused his gaze on the ball machine and was aware that a ball would

soon be released. Participants were instructed to catch as many balls as possible. Trials in which the

/N3/$"!/+-/$)$/3%$-/7)-.*-)-./$/)1*0)*)!*:%$)7/8"*-"%+)%4)-./)+%$!*')@"6.-)3*-.)H%+',)R5Jjm)%4)*'')

trials) were not examined but retaken after each session.

Dependent measures and data analysis

Catching performance was evaluated using the number of successful catches for each occlusion

(no/early/late) and each expectancy condition (expected-unexpected). Although we attempted to

control for learning within and between experimental phases by providing a familiarization phase, it was

7/#"7/7)-%)42$-./$)!"+"!"</)3%00"E'/)'/*$+"+6)/44/#-0)E,)$/0-$"#-"+6)-./)9"+/!*-"#*')*+*',0"0)-%)*)03/#"&#)

02E0/-)%4)-$"*'05)U%)-."0)/+7()1/)0/'/#-/7)-./)'*0-)&8/)-$"*'0)4%$)/*#.)%4)-./)/N3/#-/7)%##'20"%+)#%+7"-"%+0)

*+7)-./)&$0-)&8/)-$"*'0)4%$)/*#.)%4)-./)2+/N3/#-/7)%##'20"%+)#%+7"-"%+05)a"8/)+%)%##'20"%+)-$"*'0)1/$/)

selected according to a criterion that minimized any potential sequence and/or carry-over effects from

*)3$/#/7"+6)%##'20"%+)-$"*'5)O3/#"&#*'',()-./)0/'/#-/7)+%)%##'20"%+)-$"*'0)*'1*,0)3$/#/7/7)*+)/*$',)%$)*)'*-/)

occlusion trial but could not be preceded by another occlusion trial. The selected trials were subjected

1 If this analogue signal failed to detect the moment of ball-hand contact, it was derived from the 3D visual reconstruction of the catching movement in the Qualisys software program. A clearly visible sudden jerky backward movement of the index and thumb marker as a consequence of the ball impact was recognized as the moment of contact (Mazyn et al. 2007b).

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to a kinematic analysis, which was completed using proprietary motion analysis software (Visual 3D

8K5jI5J()cD!%-"%+)A+#5()=*"-./$0E2$6()]d()^OML5)U./)!*$9/$)3%0"-"%+)7*-*)1/$/)&'-/$/7)20"+6)*)0/#%+7D

%$7/$)$/#2$0"8/) '%1D3*00)P2--/$1%$-.)&'-/$)H#2-)%44)*-)RJ);<L5)O2E0/>2/+-',() -./) 4%''%1"+6)9"+/!*-"#)

variables were derived from the time-synchronised analogue signals of the optoelectronic trigger, thigh-

located switch and microphone, in combination with the 3D coordinates of the markers positioned on

the catching arm and hand:

Transport variables:

q)) B*-/+#,)-"!/)HBU()"+)!0LX)-"!/)E/-1//+)E*'')*33/*$*+#/)*+7)$/'/*0/)%4)-./)-."6.D'%#*-/7))

switch (movement onset).

q)) ]%8/!/+-)-"!/)H]U()"+)!0LX)-"!/)E/-1//+)$/'/*0/)%4)-./)-."6.D'%#*-/7)01"-#.)*+7)E*''D)

hand contact.

q)) d"03'*#/!/+-)%4)-./)1$"0-)HdNf()"+)#!LX)7"0-*+#/)E/-1//+)-./)3%0"-"%+)%4)-./)1$"0-)*-))

movement onset and ball-hand contact in the anterior-posterior axis (/-axis).

q)) Q/*9)f$"0-)i/'%#"-,)HQfi()"+)!k0LX)&$0-)3/*9)%4)-./)1$"0-)8/'%#"-,)72$"+6)-./)#*-#."+6)))

action (the momentary wrist velocity was calculated as the resultant of the velocities in

the /-, y- and 7-axis).

q)) U"!/)U%)Q/*9)f$"0-)i/'%#"-,)HUpUCpQfi()"+)!0LX)-"!/)E/-1//+)!%8/!/+-)%+0/-)*+7))

the moment of peak wrist velocity.

Grasping variables:

q)) Q/*9)%4);*+7)M3/$-2$/)HQ;M()"+)#!LX)!*N"!2!)'"+/*$)7"0-*+#/)E/-1//+)-.2!E)*+7)))

index during the unfolding of the catch2.

q)) =$*03"+6)-"!/)H=U()"+)!0LX)-"!/)E/-1//+)!*N"!2!).*+7)*3/$-2$/)*+7)E*''D.*+7)#%+-*#-5

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Given the likely deviation from normal distribution for near maximal performance (especially for no

occlusion trials), Friedman’s tests were conducted on the catching performance scores, with Wilcoxon

signed-rank post hoc tests (Sidak step-down-adjusted p values).

The trials selected for the kinematical analysis were submitted to a linear mixed model (variance

#%!3%+/+-0)1*0)-./)0/'/#-/7)8*$"*+#/)0-$2#-2$/L)1"-.)-.$//)&N/7)4*#-%$0)H/N3/#-*+#,()%##'20"%+)*+7)

-$"*')+2!E/$L)*+7)*)$*+7%!)4*#-%$)H02E:/#-L5)O"6+"&#*+-)!*"+)*+7)"+-/$*#-"%+)/44/#-0)%4)/N3/#-*+#,)*+7)

%##'20"%+)1/$/)42$-./$)*+*',</7)20"+6)*7:20-/7)'/*0-)0"6+"&#*+-)7"44/$/+#/0)HBOdL)-/0-0)Hp < 0.05).

RESULTS

M0)/N3/#-/7().*8"+6)#%!3'/-/7)-./)4*!"'"*$"0*-"%+)0/00"%+0()SI5Tbm)%4)*'')E*''0)1/$/)#*26.-)"+)-./)-/0-)

3.*0/5);%1/8/$()"+)03"-/)%4)-./)."6.)#*-#."+6)0#%$/0()-./$/)1*0)*)0"6+"&#*+-)/44/#-)%4)%##'20"%+)4%$)E%-.)

expected (!22,20

= 32.39, p < 0.001) and unexpected (!22,20

= 15.40, p < 0.001) condition. Participants

caught more balls (9.70 out of 10) in trials with no occlusion compared to both early and late occlusion

trials (on average 7.8 balls out of 10, p n)J5JJbL5)U./$/)1/$/)+%)0"6+"&#*+-)7"44/$/+#/0)E/-1//+)-./)

expected and the unexpected condition. Importantly, in almost all trials in which the ball was not caught,

there was a clear ball-hand contact, which indicates that gross spatial positioning was well maintained.

Table 1 shows the group means and inter-participant standard deviations of transport and grasping

variables. Main and interaction effects of expectancy and occlusion for each variable are also presented.

Importantly, no effects of trial number were observed, which implies that the effects of expectancy

presented in Table 1 most likely were not due to learning across the experiment.

2 For most of the participants, a clear peak near the end of the catch characterized hand aperture. However, 5 participants had a plateau shape or a double peak. PHA was then corrected 0%) -.*-) "-) $/@/#-0) -./) 0-*$-) %4)the grasping phase (i.e., a second 3/*9L)*-) -./)&+*')#'%02$/)%4) -./)hand.

99

I!B4D&<

Expectancy

A main effect of expectancy was observed for DxW, an effect that was superseded by an interaction

with occlusion (see below). There was also a main expectancy effect for PWV (see Table 1). Participants

had a higher maximal wrist velocity in the unexpected condition (p < 0.001) compared to the expected

condition. No other main effects of expectancy were found.

Occlusion

M'')9"+/!*-"#)8*$"*E'/0)0.%1/7)*)0"6+"&#*+-)!*"+)/44/#-)%4)%##'20"%+5)C##'20"%+)$/02'-/7)"+)*7*3-*-"%+0)

in the transport and grasping phase of the catching movement. These effects are summarized in Table

1. Importantly, however, some of these occlusion effects were superseded by an interaction with

expectancy (see below).

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Table 1. Q'203)20()3120(2,()('+"21"*03)d!`e)*.)62165"08)$',.*,#206')1*8'15',)-"15)1,203$*,1)20()8,23$)

+2,"2<%'3).*,)15')15,'')+"392%)*66%93"*03)d0*k'2,%:k%21'e)90(',)15')'/$'61'()20()90'/$'61'()6*0("1"*0=)!121"31"62%)

#2"0)20()"01',261"*0)'..'613)*.)*66%93"*0)20()'/$'61206:)6*0("1"*0).*,)'+',:)('$'0('01)+2,"2<%')d0)f)CDe

101

I!B4D&<

Expectancy by occlusion

A+)-./)-$*+03%$-)3.*0/()*)0"6+"&#*+-) "+-/$*#-"%+)/44/#-)1*0)4%2+7)4%$)dNf)*+7)UpUCpQfi5)U./)

expectation of a late occlusion resulted in ball-hand contact being positioned 3.8 cm further forward

compared to an expected no occlusion (p < 0.001), while in the unexpected condition, the hand was

32-)4%$1*$7)*0)"4)*)'*-/)%##'20"%+)1*0)/N3/#-/7)H_b)#!L()1"-.)+%)0"6+"&#*+-)7"44/$/+#/0)E/-1//+)+%)*+7)

late occlusion trials (see Fig. 1). The expectation of a late occlusion also resulted in an 18 ms shorter

T_TO_PWV as compared to an expected no occlusion (p < 0.005), whereas T_TO_PWV was the

same for both no and late occlusion trials in the unexpected condition.

Figure 1. Q'20)1,2N'61*,:)*.)15')-,"31)

"0)15')/7;$%20')d/;2/"3),'$,'3'013)15')20;

1',"*,;$*31',"*,)2/"3)20()7;2/"3)15')+',1"62%)

2/"3e) *.)$2,1"6"$201) O!) .*,) '265)*66%93"*0)

d0*k'2,%:k%21'e)20()'/$'61206:)d?)'/$'61;

'(F)l)90'/$'61'(ePART II

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PART IPART IIPART II

With respect to the grasp kinematics, the timing of the peak of hand aperture (GT) was characterized

E,) *) 0"6+"&#*+-) "+-/$*#-"%+) /44/#-) E/-1//+) /N3/#-*+#,) *+7) %##'20"%+5) =U)1*0) '%+6/$) 4%$) -./) /*$',)

occlusion trials than for no occlusion trials in the expected as well as the unexpected condition (p <

0.001). Late occlusion trials, however, differed between expectancy condition (p < 0.001), with GT-

values that corresponded to early occlusion trials in the expected condition and to no occlusion trials

in the unexpected condition.

103

I!B4D&<

DISCUSSION

The aim of the present experiment was to elucidate whether and how the human motor system

adapts to visual information of an approaching object that is expectedly or unexpectedly perturbed,

/*$',)%$)'*-/)72$"+6)"-0)-$*:/#-%$,5)U./)!*"+)&+7"+60)%4)-."0)0-27,)$/8/*')-.*-)-./)%E0/$8/7)*7*3-*-"%+0)

to visual occlusions differed when participants were aware in advance of the impending visual condition

(i.e., whether there would be an early, late or no visual occlusion).

In contrast to our predictions, movement onset was not affected by the explicit advance knowledge

%4)*+)23#%!"+6)%##'20"%+5);%1/8/$()72$"+6)-./)2+4%'7"+6)%4)-./)#*-#."+6)!%8/!/+-()-./$/)1/$/)0"6+"&#*+-)

differences between the expected and unexpected condition, although these mostly depended on the

visual information available (i.e., interaction effect, see below). An exception was the slightly higher wrist

velocity peak for the unexpected condition compared to expected condition (see also Daum et al.

2007). In the absence of advance knowledge, such an observed adaptive response is suggested to give

increased opportunities to overcome an uncertain situation (Tijtgat et al. 2010).

Compared to when no occlusion was expected, peak of the wrist velocity was reached earlier

and forward displacement of the wrist (DxW) was increased when it was known in advance (i.e.,

expected late), or there was uncertainty (i.e., unexpected no and late) that there would be a late

%##'20"%+)H"5/5()6%66'/0)1%2'7)%$)#%2'7)E/)%##'27/7) 4$%!)TJJ)!0)*4-/$) $/'/*0/)2+-"') -./)&+*')#*-#.L5)

A different strategy was evident in early occlusion trials, where a time-buying strategy was evident in

the gross motor orientation of the hand, irrespective of advance knowledge. Indeed, when vision was

occluded between 200 ms and 600 ms after release, participants located the wrist earlier and closer

to the body, which delayed ball-hand contact and thereby increased the time that the ball was visible

toward the end of the trial (Fig. 1, see also the increased MT). Such an adaptive strategy enabled

participants to take advantage of online control processes and thus minimize any errors that resulted

from not having access to vision during the early occlusion.

In the grasping phase, the greater peak hand aperture for occlusion trials corroborates earlier

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research (Wing et al. 1986; Jakobson and Goodale 1991; Fukui and Inui 2006; Mazyn et al. 2007a;

f."-1/'')/-)*'5)IJJj()IJJSL()1."#.).*0)0266/0-/7)-.*-) "+#$/*0/7)3/*9)*3/$-2$/)$/@/#-0)-./)20/)%4)*)

safety margin when vision is occluded. In the current study, hand aperture was presumably increased in

early and late occlusion trials because participants had restricted access to important visual information

4$%!)E*'')@"6.-5)d"44/$/+#/0)"+)6$*03"+6)-"!/)*0)*)42+#-"%+)%4)/*$',)%##'20"%+0)1/$/)#%+0"0-/+-)1"-.)-.%0/)

%4)3/*9)*3/$-2$/)*+7) $/@/#-/7) -./) "+#$/*0/7) -"!/)+//7/7) -%)#'%0/) -./).*+7)1./+) "-)1*0)%3/+/7)

1"7/$5)M'0%()*+)"+@2/+#/)%4)*78*+#/)9+%1'/76/)%+)6$*03"+6)-"!/)1*0)%E0/$8/7)4%$)'*-/)%##'20"%+)-$"*'05)

Grasping time was longer when a late occlusion was announced a priori. However, when such a late

%##'20"%+)#%2'7)+%-)E/)*+-"#"3*-/7()03/#"&#)*7*3-*-"%+0)%4)-./)-"!"+6)%4)-./)6$*03)1/$/)'*#9"+6)0%)-.*-)

grasping time was equal to trials with no occlusion (see Table 1). Such adaptations to the grasping

phase of catching contrast with previous work that has reported invariant timing across various task

constraints (Savelsbergh et al. 1991, 1993; Laurent et al. 1994; Bennett et al. 1999; Mazyn et al. 2006;

Tijtgat et al. 2010), as well as in the face of perturbations (Polman et al. 1996; Button et al. 2000; Mazyn

et al. 2007a), although it has been previously reported at individual level (Button et al. 2000, 2002) .

Taken together, the observed differences between expected and unexpected occlusion trials suggest

*+)"+@2/+#/)%4)/N3'"#"-)*78*+#/)9+%1'/76/)%+)!%8/!/+-)/N/#2-"%+5)U."0)"+-/$3$/-*-"%+)#.*''/+6/0)-./)

suggestion of a visuomotor system that is mainly regulated by trial-by-trial history with only a marginal

"+@2/+#/)%4)/N3'"#"-)*78*+#/)9+%1'/76/)H7/)B200*+/-)/-)*'5)IJJI[)O%+6)*+7)W*9*,*!*)IJJZ[)f."-1/'')

et al. 2008, 2009). Notwithstanding the undeniable adaptive process based on previous trials (Scheidt

et al. 2001; Zago et al. 2010), it is our contention that explicit (i.e., conscious or declarative) advance

9+%1'/76/)#*+)*'0%)/N/$-)*+)"+@2/+#/)%+)-./).2!*+)3/$#/3-2%D!%-%$)0,0-/!)Hf"''"+6.*!)/-)*'5)RSjS[)

Willingham 1998). Accordingly, both trial-by-trial adaptations and cognition could affect kinematics on the

#2$$/+-)-$"*')HP/++/--)/-)*'5)IJRJL()*'-.%26.)-."0)"0)'"9/',)-%)E/)"+@2/+#/7)E,)-./)03/#"&#)-*09)#%+0-$*"+-0)

(i.e., duration and locus of occlusion, nature of eye movements required to track the approaching ball).

A+7//7()1."'/)*)#%!!%+)+/2$*')+/-1%$9).*0)E//+)"7/+-"&/7)4%$)3$%#/72$*')*+7)7/#'*$*-"8/)'/*$+"+6()

additional brain regions (i.e., posterior parietal, superior parietal and dorsal prefrontal cortex) have

been shown to be activated when explicit advance (declarative) knowledge was provided in sequence

learning (Willingham et al. 2002).

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SUMMARY AND IMPLICATIONS

This study showed that explicit advance knowledge regarding the upcoming availability of visual

"+4%$!*-"%+) "+@2/+#/0) -./) *7*3-"8/) E/.*8"%$5) O2#.) &+7"+60) *$/) +%-) #%+0"0-/+-) 1"-.) *) 0"!3'/) 3$"%$)

history effect (i.e., trial-by-trial adaptation), since this would not predict consistent differences between

expectancy conditions. Indeed, in the current study, prior task history was equal for both conditions

(randomly assigned occlusion trials). Therefore, the current results add to the call to consider expectancy

as 20)"#$*,1201)6*031,2"01)*0)#*+'#'01)3:31'#3 (Davids and Button 2000, p. 515). In this way, a tennis

players’ fast reaction will be affected by the advance knowledge of the opponents preferred shooting

7"$/#-"%+():20-)'"9/)0%!/%+/G0)1*'9"+6)3*--/$+)1"'')#.*+6/)1./+)*)0'"33/$,)@%%$)"0)*++%2+#/7)E/4%$/)H0//)

also Marigold and Patla 2002). As such, expectancy should not be disregarded in future experimental

methodologies.

ACKNOWLEDGEMENTS

The authors are grateful to Cindy Lowyck and Arnout Sercu for their help in data collection. We

also thank two anonymous reviewers for their helpful comments on earlier versions of this paper.

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U3:65*%*8:W)[9#20)U',6'$1"*0)20()U',.*,#206'F)MS, 1040-1055

Vince MA (1948) Corrective movements in a pursuit task. X92,1',%:)N*9,02%)*.)'/$',"#'012%)$5:3"*%*8:)

20()6*8021')#'("62%)36"'06'3F)E, 85-103

Whiting HTA, Sharp RH (1974) Visual occlusion factors in a discrete ball-catching task.) O*9,02%)*.)

Q*1*,)R'52+"*,F)S, 11-16

f."-"+6);UM()="'')gP()O-/3./+0%+)h])HRSZJL)c$"-"#*')-"!/)"+-/$8*'0)4%$)-*9"+6)"+)@"6.-)"+4%$!*-"%+)"+)

a ball-catching task. ?,8*0*#"63F)EM, 265-272

Whiting HTA, Alderson GJK, Sanderson FH (1973) Critical time intervals for viewing and individual

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Whitwell RL, Goodale MA (2009) Updating the programming of a precision grip is a function of

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Whitwell RL, Lambert LM, Goodale MA (2008) Grasping future events: explicit knowledge of the

*8*"'*E"'"-,)%4)8"02*')4//7E*#9)4*"'0)-%)$/'"*E',)"+@2/+#/)3$/./+0"%+5)?/$',"#'012%)R,2"0)K'3'2,65F)EPPF)603-

611

Willingham DB (1998) A neuropsychological theory of motor skill learning. U3:65*%*8"62%)K'+"'-F)EDG,

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Willingham DB, Nissen MJ, Bullemer P (1989) On the development of procedural knowledge.

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Willingham DB, Salidis J, Gabrieli JDE (2002) Direct comparison of neural systems mediating

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Wing AM, Turton A, Fraser C (1986) Grasp size and accuracy of approach in reaching. O*9,02%)*.)

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Winges SA, Weber DJ, Santello M (2003) The role of vision on hand preshaping during reach to

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Woodworth RS (1899) The accuracy of voluntary movement. U3:65*%*8"62%)K'+"'-F)M (Monograph

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Zago M, Iosa M, Maffei V, Lacquaniti F (2010) Extrapolation of vertical target motion through a brief

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movements. O*9,02%)*.)Q*1*,)R'52+"*,F)EG, 217-236

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[ABSTRACT] The purpose of this study was to investigate to which extent postural adjustments in response to raising the arm in ball catching resemble those as commonly seen in a reaction-time arm raising task. To this end, full-body kinematics, kinetics and postural muscle activity were measured. The arm raising movement in #*-#."+6) 0.%1/7)IT)7/6$//0)!%$/) /'E%1)@/N"%+) -.*+) -./) $/*#-"%+D-"!/) -*095)U./)consequently smaller changes in momentum in anterior-posterior direction resulted in altered corrective horizontal ground reaction forces and centre of pressure deviations. Initial postural adjustments appeared to support the initial arm raising movement by segment stabilization. Afterwards, an inverted pendulum mechanism was suggested as subsequent equilibrium control for catching, whereas additional segmental counter rotation was observed in the reaction-time task. These results indicate that postural adjustments for arm raising can conceptually differ between similar tasks depending %+)-./)03/#"&#)-*09)#%+0-$*"+-05

[KEYWORDS] Postural adjustments; Catching; Arm raising; Segment stabilization; Equilibrium control

BASED ON: Tijtgat P, Vanrenterghem J, Bennett SJ, De Clercq D, Savelsbergh GJP, Lenoir M. (In revision) Postural adjustments in catching: on the interplay between segment stabilization and equilibrium control. Q*1*,)A*01,*%

STUDY 3: POSTURAL ADJUSTMENTS IN CATCHING: ON THE INTERPLAY BETWEEN SEGMENT

STABILIZATION AND EQUILIBRIUM CONTROL

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I!B4D&PX&6EI!B^@C&@4lBI!F9;!I&G;&A@!AHG;:X&E;&!H9&G;!9^6C@D&c9!]99;&I9:F9;!&I!@cGCGm@!GE;&@;4&9nBGCGc^GBF&AE;!^EC&

INTRODUCTION

While interceptive actions such as catching have been extensively investigated in order to gain

further insight in how the human perceptual-motor system is organized (Zago et al. 2009), less attention

has been paid to the role that postural control might play during such actions. This is relevant because

some experiments have shown postural balance might be decisive for successful catching performance in

childhood. For example, performance in poor catchers was found to approach the level of good catchers

when sitting or with the aid of a support (Davids et al. 2000; Angelakopoulos et al. 2005; Savelsbergh et

al. 2005). Several other studies of catching have shown that prior to responding by moving the relevant

effectors, there is an anticipatory muscle contraction in muscles that are responsible for postural control

(Shiratori and Latash 2001; Li and Aruin 2007, 2009). However, these experiments focused on postural

adjustments when a ball was falling down, and hence did not demand an actual reaching movement that

would disturb postural balance. Catching an approaching object while standing demands at least some

postural control in response to raising the arm upwards and towards the object, as well as eventually

controlling postural disequilibrium as a consequence of expected and actual mechanical impulse of the

E*'')*#-"+6)%+)-./).*+7)H/565()#$"#9/-)&/'7"+6().*+7E*''L5)

In the past decades, many studies have been devoted to the analysis of coordination between the

focal movement of arm raising and its concomitant postural adjustments to maintain equilibrium. This

was typically studied in the task of raising the arm from the vertical downward (arm besides the body)

to the horizontal forward position. When raising the arm while standing, body posture is disturbed for

two reasons (Massion 1992). First, a moving segment causes a quick change of the geometry of the

body which leads to a forward acceleration of the segment and whole body centre of mass (COM; Fig

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1a). Second, the internal forces caused by this acceleration of the prime mover results in reaction forces

on the supporting segments (Fig 1b). To counteract the destabilizing consequences of these forces, the

central nervous system is suggested to exhibit anticipatory postural adjustments (APA; Bouisset and

Zattara 1987; Zattara and Bouisset 1988). APA is believed to occur simultaneously with, or just before,

the initiation of the voluntary movement by a feedforward control mechanism (Cordo and Nashner

1982). For self-paced arm raising (Bleuse et al. 2002; Hirschfeld 2007; Girolami et al. 2010; Aimola et

al. 2011) as well as raising one or both arms as a reaction to an auditory or visual stimulus (Aruin

and Latash 1995; Hodges et al. 1999; Cuisinier et al. 2005; Bleuse et al. 2006, 2008), the mechanical

effect of APA has been reported as a backwards shift of the centre of pressure (COP) starting before

!%8/!/+-)%+0/-5)U."0).*0)E//+)"7/+-"&/7)*0)*+)"+8/$-/7)3/+72'2!)!/#.*+"0!)*-)-./)'/8/')%4)-./)*+9'/)

to generate anticipatory forward acceleration of the whole body COM to compensate for the ensuing

inertial forces from prime mover motion (Fig. 1a). However, the functional role of these observations

as actual APA has recently been questioned (Pozzo et al. 2001; Patla et al. 2002). By comparing model-

based with experimental data, it has been suggested that the initial postural control of COM at the

level of the ankle is passive and that APA are better explained by local segment stabilization to counter

reactive torques acting on the shoulder rather than to compensate the destabilizing effect from small

forward acceleration of whole body COM (Fig. 1b).

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Figure 1. B5'0),2"3"08)15')2,#)-5"%')3120("08F)<*(:)$*319,')"3)("319,<'().*,)1-*),'23*03=)a)K2"3"08)15')

2,#)6293'3)2)b9"64)65208')*.)15')8'*#'1,:)*.)15')<*(:)-5"65)%'2(3)1*)2).*,-2,()266'%',21"*0)*.)15')6'01,')

*.)#233)*.)15')2,#)dA>Qarme)20()-5*%')<*(:)dA>Q

<*(:e=)b)@5')"01',02%).*,6'3)6293'()<:)15"3)266'%',21"*0)*.)

15')2,#),'39%13)"0),'261"*0).*,6'3)*0)15')39$$*,1"08)3'8#'013

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After the initial movement impulse and its destabilizing effects, subsequent postural adjustments

are required to regain postural equilibrium. Besides the standard inverted pendulum mechanism which

is controlled at the level of the ankle and controls displacement of the COP, an additional segmental

counter-rotation mechanism exists which acts primarily at hip-level and is often required to retain

balance in more destabilizing situations (Hof 2007). The latter counter-rotation mechanism involves

increased horizontal ground reaction forces (GRF) which generate linear accelerations of the whole

body COM, in contrast to the former mechanism which relates to torque generation at the ankle and

leads to displacement of COP. In other words, the inverted pendulum mechanism translates the GRF

vector whereas the segmental counter-rotation mechanism rotates the GRF vector.

From the above studies, it remains unclear whether the postural control mechanisms observed for

arm raising can be generalized across actions that differ in task constraints. Therefore, the aim of present

experiment was to ascertain if postural control mechanisms that were typically observed in well-studied

internally driven arm raising tasks would also be present in a similar arm raising task with a different, i.e.,

externally driven, action goal. Unconstrained one-handed catching requires a precise spatiotemporal

coordination of the catching arm in relation to the approaching ball (Tijtgat et al. 2010) in order to bring

the catching hand to the right place at the right time, whereas raising the arm in reaction to an external

stimulus demands less complex and internally driven intra-limb coordination. Therefore, kinematics,

kinetics and postural muscle activation of raising the arm at high velocity in unconstrained real ball

catching was compared to that of an arm raising reaction-time task. Differences in postural adjustments

E/-1//+)-./0/)-*090)#%2'7)0./7)0%!/)'"6.-)%+).%1)-./).2!*+)0,0-/!)!%7"&/0)3%0-2$*')*7:20-!/+-0)

7/3/+7"+6)%+)-./)03/#"&#)-*09)#%+0-$*"+-5

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METHODS

Participants

Six male self-declared right handed participants (aged between 21 and 23, mean weight 74.9 ±

7 kg and mean height 180.3 ± 4 cm) gave their written informed consent (approved by the Ethical

Committee of the host University) before participating.

Materials and procedure

Participants were asked to stand still with their feet parallel (two marked lines) on a force plate

(AMTI, 1000 Hz), arms besides the body and head upright with gaze located straight ahead. The

experiment consisted of 10 trials of two tasks in successive order: catching (CATCH) and a reaction-

time action (RAISE). In CATCH, participants were instructed to catch yellow, mid-pressured tennis

balls. In RAISE, they were instructed to raise their right arm as fast as possible until horizontal from the

moment they saw a ball coming out of a ball machine. At the completion of the movement, the end

position was retained for more than 3 seconds so that a new equilibrium-position was established. Balls

were launched at a speed of 15.8 ± 0.16 m/s at 8.4 m from the participant’s frontal plane by a ball-

projection machine (Promatch/Mubo B.V., Gorinchem, The Netherlands). The machine was covered

with black plastic that had a small cut-out section through which the balls were released so that

participants could not anticipate ball delivery. For CATCH, launch angle was adjusted so that balls

arrived above participant’s right shoulder. For RAISE, launching angle was changed so that while balls

were still delivered towards the participant, they could not reach the participants’ body. Participants

wore headphones that minimized sound generated by the ball machine and a face shield to protect the

4*#/()1."'/)+%-)7"0-2$E"+6)*##/00)-%)-./)42'')8"02*')&/'75)U.$//D7"!/+0"%+*')9"+/!*-"#)7*-*)1/$/)#%''/#-/7)

*-) IJJ);<)20"+6) RI) "+4$*$/7) #*!/$*0) HQ$%$/@/N()r2*'"0,0)MP()=%-./+E2$6() O1/7/+L5)]*$9/$0)1/$/)

bilaterally placed on distal phalanx of hallux and digitus minimus, lateral and medial aspect of calcaneus,

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malleolus and femoral condyles, iliac crest, anterior and posterior superior iliac spine, sternum, C7,

intertubercular sulcus of humerus, styloid process of radius and ulna, distal phalanx of thumb and index.

Electromyographic (EMG) data were recorded using an 8-channel wireless EMG system (Noraxon

ZeroWire). Disposable circular (diameter 10 mm) biporal surface electrodes were placed on right

rectus abdomninis (RA), erector spinae (ES), rectus femoris (RF), biceps femoris (BF), tibialis anterior

(TA) and gastrocnemius (GA). The skin of the participants was prepared by shaving and cleaning with

alcohol. Pre-gelled Ag/AgCl circular electrodes were placed at 20 mm parallel parallel to the muscle

&E/$0)-%)$/72#/)"!3/7*+#/5)g'/#-$%7/0)1/$/)3'*#/7)"+)*##%$7*+#/)1"-.)-./)$/#%!!/+7*-"%+)4$%!)-./)

OgWAM]D3$%:/#-)-%)-./)03/#"&/7)0/+0%$)'%#*-"%+)3/$)!20#'/)H;/$!/+0)/-)*'5)RSSSL5)g]=D0"6+*'0)1/$/)

$/#%$7/7)1"-.)*)0*!3'"+6)4$/>2/+#,)%4)RJJJ);<()3$/D*!3'"&#*-"%+)6*"+)%4)RJJJ[)*+7)"+-/6$*-/7)1"-.)-./)

Qualisys motion capturing system.

Data processing

`"+/-"#()9"+/!*-"#)*+7)g]=)7*-*)1/$/)$/#%$7/7)0"!2'-*+/%20',)*+7)&'-/$/7)H'%1D3*00)P2--/$1%$-.)

&'-/$()RJ);<L5)U./)g]=D0"6+*'0)1/$/)*'0%)."6.D3*00)&'-/$/7)HbJ);<L()$/#-"&/7)*+7)+%$!*'"</7)-%)g]=D

activity during a stand-still period of 30 seconds. Due to a technical problem, BF- and TA-signals of three

participants were excluded. A 14-segment model consisting of feet, shanks, thighs, pelvis, thorax/abdomen,

upper arms, lower arms and hands was developed using Visual 3D (C-Motion Inc., Gaithersburg, MD,

USA).

A+)%$7/$)-%)#%!3*$/)cMUc;)*+7)YMAOg()@/N"%+)*+7)/N-/+0"%+)*+6'/0)1/$/)#*'#2'*-/7)4%$)/'E%1()

shoulder, hip and ankle and expressed relative to their baseline level (between 500 and 300 ms before

movement onset). COP anterior-posterior displacement was also expressed relative to the average

position between 500 and 300 ms before movement onset. Onsets were calculated according to the

criterion that the acceleration of the signal had to exceed 0.5 m/s" for at least 25 ms. Onset of arm

movement (t0) was derived from the forward acceleration of the wrist. Onset of postural adjustments

was derived from the anterior or posterior acceleration of COP. Movement time (MT) was the time PART II

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between t0 and the end of the deceleration phase (t

end).

U./)"!3*#-)%4)$*"0"+6)-./)*$!)1*0)>2*+-"&/7)4%$)E%-.)-*090)E,)#*'#2'*-"+6)cC]D7"03'*#/!/+-)*+7)

changes in momentum of key segments of the moving body. COM and momentum of the whole body

(body), the right arm (consisting of right upper arm, lower arm and hand) and the body without the

right arm (rest of body), were derived. Muscular activation of trunk (RA and ES), upper leg (RF and BF)

*+7)'%1/$)'/6)HUM)*+7)=ML)!20#'/0)1*0)>2*+-"&/7)0"+#/)-./0/)!20#'/0)1/$/)/N3/#-/7)-%)6/+/$*-/)

"!3%$-*+-)42+#-"%+0)"+)0/6!/+-)0-*E"'"<*-"%+)*+7)/>2"'"E$"2!)#%+-$%'5)a"+*'',()!20#'/)*#-"8*-"%+()@/N"%+)

and extension angles of hip and ankle together with resultant anterior-posterior COP-displacement and

GRF were integrated to enable a conclusive analysis of the equilibrium control mechanisms as suggested

by Hof (2007).

Statistical analysis

Intra-participant mean data from 10 successful trials for CATCH and RAISE were calculated.

Statistical tests consisted of non-parametric Wilcoxon tests. PD8*'2/0)1/$/)#%+0"7/$/7)0"6+"&#*+-)1./+)

p < 0.05.

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RESULTS

Arm movement

Both CATCH (390 ± 18 ms) and RAISE (350 ± 53 ms) had similar movement times (z = -1.572,

03L)*+7)*)#%!3*$*E'/)*##/'/$*-"%+D7/#/'/$*-"%+)3$%&'/)%4)-./)1$"0-()-.%26.)1"-.)!%$/)3$%!"+/+-)3/*9)

amplitudes for RAISE (7 = -2.207, p < 0.05, Fig. 1). Joint angles in shoulder and elbow showed that both

*$!)$*"0"+6)!%8/!/+-0)1/$/)3/$4%$!/7)7"44/$/+-',5)g'E%1)@/N"%+)1*0)'*$6/$)4%$)cMUc;)H7 = -2.207,

p)n)J5JbL)*0)#%!3*$/7)-%)YMAOg5)A+)cMUc;()02E0-*+-"*')/'E%1)@/N"%+)HKb)l)K)7/6L)*-)-0 preceded

0.%2'7/$)@/N"%+()1./$/*0)"+)YMAOg()%+',)0.%2'7/$)@/N"%+)%##2$$/7)-%6/-./$)1"-.)%+',)0!*'')*+7)8*$"*E'/)

/'E%1)@/N"%+)HRS)l)RI)7/6L5)U."0)1*0)*00%#"*-/7)1"-.)*)RJ)#!)'/00)4%$1*$7)7"03'*#/!/+-)%4)-./)cC])

of the arm in CATCH as compared to RAISE (7 = -2.207, p < 0.05; Fig. 2).

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Figure 2. ^66'%',21"*0)*.)-,"31F)

2089%2,) ("3$%26'#'01) *.) ) '%<*-)

20() 35*9%(',) 20() ("3$%26'#'01)

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tDF)3'6*0()+',1"62%)%"0')"3)1

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Postural adjustments

No clear backward shift in COP before t0 was observed in RAISE, except for subject JC (Fig. 3).

Onset of COP-shift was reached on average at 33 ± 24 ms (CATCH) and 13 ± 73 ms after t0 (RAISE),

*+7)1*0)+%-)0"6+"&#*+-',)7"44/$/+-)E/-1//+)#%+7"-"%+0)H7 = -0.943, 03).

Figure 3.) A>U;("3$%26'#'01)

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K^\!?) d,"851) $20'%e) 2,*90() 1D=)^%%)

1,"2%3).*,)M)39<N'613)2,'),'$,'3'01;

'(=)>03'1)*.)A>U)"3)"0("621'()-"15)

1"643=)T',1"62%)%"0')"3)1D

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Figure 3

( c o n t i n u e d ) .

A>U;("3$%26'#'01)

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d%'.1) $20'%e) 20()

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I!B4D&P

Raising the arm resulted in a similar forward displacement of arm COM and arm momentum for

both CATCH and RAISE (Fig. 4). This was compensated by a backward displacement of COM of the

rest of the body, and an opposing momentum of the rest of the body that closely matched the arm

movement. The net result of the interplay between the displacements of arm and rest of body was

a forward displacement of the whole body COM. Apart from these similarities, however, there were

some important differences between CATCH and RAISE. The acceleration of arm COM was initiated

8 ± 10 ms before t0 in RAISE, whereas it was delayed to 26 ± 6 ms after t

0 in CATCH (7 = -2.201,

p < 0.05). Also, a greater forward momentum of the rest of the body was observed for CATCH as

compared to RAISE (7 = -2.207, p < 0.05). Finally, whole body COM returned to baseline after the end

of the movement in CATCH whereas it remained forward in RAISE.

Figure 4. ^,#F) <*(:)

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2,') $,'3'01'(=) ]",31)

+',1"62%)%"0')"3)1DF)3'6*0()

+',1"62%)%"0')"3)1'0(

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PART IPART IIPART II

For CATCH, early activation of BF and an initial forward GRF-shift was observed, followed by a

0'"6.-)."3)@/N"%+)*+7)*)E*#91*$7)=YaD0."4-()1."'/)YM)*+7)gO)#%+-$*#-/7)0"!2'-*+/%20',)Ha"65)bL5)O'"6.-',)

increased activity of BF extended the hip in the second part of the catching phase and shifted GRF

4%$1*$7)*6*"+5)M-)-./)*+9'/):%"+-()*#-"8*-"%+)=M)1*0)%E0/$8/7)4%$)-./)&$0-)RIJJ)!0)*4-/$)-0 that resulted

"+)*)0!*'')3'*+-*$)@/N"%+)"+)-./)*+9'/)*+7)*)4%$1*$70)0."4-)%4)cCQ)Ha"65)TL5)UM)#%+-$*#-"%+)+/*$)-./)/+7)

%4)!%8/!/+-)#*20/7)7%$0"@/N"%+)"+)-./)*+9'/)*+7)$/-2$+/7)-./)cCQ)E*#91*$705)

For RAISE, there was an early activation burst of BF and ES, turning the initial posterior GRF rapidly

to a forward GRF. Flexion of the hip was enhanced by activation of RF and RA (Fig. 5) and resulted in

a backward shift of GRF. Finally, the hip was extended again to baseline level as seen in the increased

*#-"8*-"%+)%4)Pa)*+7)gO5)Q'*+-*$)@/N"%+)"+)-./)*+9'/)1*0)*'0%)%E0/$8/7()-%6/-./$)1"-.)*)cCQ)-.*-)1*0)

initially shifted forward (Fig. 6). However, differently to CATCH, reciprocal activation of TA and GA

$/02'-/7) "+) *)E*#91*$7) $/-2$+) 4%''%1/7)E,) 4%$1*$7) 0."4-)%4)cCQ5)M4-/$)!%8/!/+-)&+*'"<*-"%+)cCQ)

returned back to baseline level.

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I!B4D&P

Figure 5. A*901',;,*121"08)

#'6520"3#=) !1"64;("28,2#) *.)

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is tDF)3'6*0()+',1"62%)%"0')"3)1

'0(PART II

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Figure 6. \0+',1'() $'0(9;

%9#)#'6520"3#=)!1"64;("28,2#)

*.)$2,1"6"$201)`Q)d,*121"*0)21)

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]",31) +',1"62%) %"0') "3) 1DF) 3'6*0()

+',1"62%)%"0')"3)1'0(

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DISCUSSION

The current study compared postural adjustments during movements involving similar arm raising

but with different task constraints, and thereby examined whether the observed postural adjustments

were likely for segment stabilization or equilibrium control. Despite its similar forward acceleration-

7/#/'/$*-"%+)3$%&'/)%4)-./)1$"0-()-./)$/03%+0/)E/6*+)1"-.)!%8/!/+-)%4)-./)0.%2'7/$)"+)YMAOg)1."'0-)

-."0)1*0)3$/#/7/7)E,)@/N"%+) "+) -./)/'E%1) "+)cMUc;5)U."0)7"44/$/+#/) "+)!%8/!/+-)9"+/!*-"#0).*7)

$/3/$#200"%+0)%+)3%0-2$*')*7:20-!/+-0)*+7)"0)7"0#200/7)E/'%1()&$0-)1"-.)$/4/$/+#/)-%)cCQ)"+)-./)#%+-/N-)

of APA, and second in relation to the interplay between initial segment stabilization and subsequent

equilibrium control.

Backwards shift of COP as APA

The presence of APA has typically been evidenced by a consistent backward shift of COP-

displacement before t0 (Aruin and Latash 1995; Hodges et al. 1999; Cuisinier et al. 2005; Hirschfeld

2007; Girolami et al. 2010; Aimola et al. 2011), and in previous literature has been represented by

mean values from single representative subjects. In this experiment, however, no representative subject

could be selected. On the contrary, our results showed large intra- and inter-subject variability in COP-

displacement at t0 (Fig. 3), with backwards and forwards shifts, as well as no shifts. Other studies have

also failed to show a consistent backward movement of the COP before movement onset (De Wolf

et al. 1998; Nougier et al. 1999; Hay and Redon 2001; Ferry et al. 2004; Mochizuki et al. 2004). While

such variability has rarely been reported in literature on APA in arm raising, it is notable that there is

some suggestion from work on catching a falling ball with an outstretched arm that “signals obtained

from force plate showed large variability across subjects” (Shiratori and Latash 2001, p. 1251). Besides

-./)*E%8/)#%+@"#-"+6)&+7"+60)"+)-./)'"-/$*-2$/()-./)3$/0/+#/)%4)0!*'')/'E%1)@/N"%+)%E0/$8/7)"+)#2$$/+-)

RAISE task may be another explanation for altered postural adjustments compared to some of the

'"-/$*-2$/()0"+#/)$*"0"+6)-./)*$!)1./+)-./)/'E%1)"0)@/N/7)"+8%'8/0)'/00)7/0-*E"'"<*-"%+)H8*+)7/$)a"-0)/-)PART II

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*'5)RSSj[)P'/20/)/-)*'5)IJJT()IJJjL5)U*9/+)-%6/-./$()-./0/)&+7"+60)"+7"#*-/)-.*-)-./)3$%3%0/7)E*#91*$7)

shift of COP before movement onset is not a ubiquitous indicator of APA, and that if APA is considered

present its functional role should be questioned.

APA for segment stabilization

The functional role of APA as a means to stabilize the body by simply counteracting COM-

displacement through an inverted pendulum behaviour has recently been questioned (Pozzo et al. 2001;

Patla et al. 2002). Initial motion of whole body COM might be a passive consequence of reaction forces

due to counter-rotating segments rather than an active control of postural equilibrium. Raising the arm

results in reaction forces acting on the rest of the body (Fig. 4). The effects of these reaction forces were

compensated by early postural adjustments as seen through muscle activations. These are considered

anticipatory because reactive responses would occur later due to transmission and electromechanical

7/'*,0)HQ*-'*)/-)*'5)IJJIL5)O2#.)*+-"#"3*-%$,)#%+-$%')E,)3%0-2$*')!20#'/0).*0)3$/8"%20',)E//+)"7/+-"&/7)*0)

a segment stabilization strategy (Patla et al. 2002). In the current study, evidence for anticipatory joint

0-*E"'"<*-"%+)1*0)4%2+7)"+)-./)/*$',)*#-"8*-"%+)%4)Pa)*+7)gO)"+)YMAOg()1."#.)3$/8/+-/7)."3)@/N"%+)-.*-)

would passively occur immediately when raising the arm (Pozzo et al. 2001; see Fig. 5). For CATCH,

different anticipatory postural adjustments were observed. Co-activation of RA and ES resulted in

bracing of the hip joint, while BF activation minimized the disturbing effects that would passively occur

by raising the arm. From these observations it is suggested that the functional role of these anticipatory

muscle activations is more likely to be segment stabilization than equilibrium control. Active equilibrium

control of the whole body COM is suggested to occur only 200 ms after t0 (Patla et al. 2002).

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I!B4D&P

!"#$%#&'()*(%&+#,-."/%"01-#,2'3,#%4+.%#-5#'6-'3,%'6-)/)5.)-2%control

After the initial movement impulse, the displaced whole body COM (Fig. 4) by raising the arm was

responded to in both tasks by consequent postural adjustments. However, the interplay between the

initial segment stabilization and subsequent equilibrium control are suggested to yield different postural

strategies between CATCH and RAISE based on task constraints. For CATCH, after initial segment

stabilization, an inverted pendulum strategy at the level of the ankle was found to be the predominant

postural strategy (Hof 2007), with muscle activity and angular displacement at the ankle explaining

-./)cCQD0."4-05)d2/)-%)0/6!/+-)0-*E"'"<*-"%+() -./)."3) :%"+-)1*0)%+',)!*$6"+*'',)@/N/7() 4%''%1/7)E,)*)

hip extension and forward momentum of the rest of the body that could be attributed to a postural

control mechanism to overcome the impact of the ball at the hand. For RAISE, the larger and dynamic

."3)@/N"%+D/N-/+0"%+)#%23'"+6)0266/0-0)*)#%2+-/$D$%-*-"+6)!/#.*+"0!)*-)."3) '/8/') "+)*77"-"%+)-%)-./)

inverted pendulum mechanism. As such, a combination of counter-rotation at the hip and inverted

pendulum at the ankle emerged in order to maintain equilibrium (Hof 2007).

The observed differences in postural adjustments are likely to be related to the larger inertial forces

generated in RAISE compared to CATCH (larger arm acceleration and momentum changes, Fig. 4).

The greater forward momentum of the rest of the body around tend

in CATCH can be explained by a

postural control mechanism to overcome the impact of the ball at the hand and is therefore different

from RAISE. Clearly, the differences in postural control between both tasks indicate that postural

*7:20-!/+-0)-%)8%'2+-*$,)!%8/!/+-0)*$/)#'%0/',)$/'*-/7)-%)03/#"&#)-*09)#%+0-$*"+-05)a2-2$/)1%$9)#%2'7)

reveal how postural adjustments might differ between different spatial or temporal constraints during

interceptive actions.

Finally, some limitations of the present study have to be acknowledged. This study was limited to

a sagittal plane analysis only considering the anterior-posterior direction of movement. Accordingly,

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*N"*')$%-*-"%+0)-.*-)#%2'7)"+@2/+#/)/>2"'"E$"2!)#%+-$%')72$"+6)2+"'*-/$*')*$!)$*"0"+6)1/$/)+%-)*+*',</7)

HP%2"00/-)s)\*--*$*()RSjZL5)M'0%()-./)%E0/$8/7)&+7"+60)%+',)*''%1)-%)0266/0-)3%00"E'/)3%0-2$*')#%+-$%')

strategies. A future in depth analysis through forward dynamic simulations could establish the true

causative nature between reaction forces due to the prime mover and concomitant postural adjustments.

Finally, regarding the EMG-data, it should be acknowledged that the present analysis was limited to a

qualitative analysis. For future research, quantitative analyses (with respect to the magnitude and timing

of the muscle contractions) deem necessary to verify whether the current indicative observations can

be further supported.

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CONCLUSION

During arm raising for a reaction-time task or for unconstrained catching, initial postural adjustments

by feedforward control seem to be a consequence of the inertia of the movement itself (segment

stabilization), rather than a mechanism to overcome possible future disequilibrium. Afterwards, an

inverted pendulum mechanism accommodates equilibrium control when raising the arm for catching,

while compensatory postural adjustments by an inverted pendulum and additional counter-rotating

mechanism to maintain balance is suggested for raising the arm in a reaction-time task. Therefore,

when studying postural control mechanisms, it should be acknowledged that the purpose of achieving

different goals might lead to different postural adjustments, notwithstanding that both disturb body

posture in a similar way by raising the arm.

ACKNOWLEDGEMENTS

The authors acknowledge Davy Spiessens for his technical support. We would also like to thank

David Rimbaut and Jacob De Troyer for their assistance in data collection.

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Ferry M, Martin L, Termoz N, Cote J, Prince F (2004) Balance control during an arm raising movement

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Hay L, Redon C (2001) Development of postural adaptation to arm raising. ?/$',"#'012%)R,2"0)

K'3'2,65F)EML, 224-232

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Hirschfeld H (2007) Motor control of every day motor tasks: Guidance for neurological rehabilitation.

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Hodges P, Cresswell A, Thorstensson A (1999) Preparatory trunk motion accompanies rapid upper

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Hof aL (2007) The equations of motion for a standing human reveal three mechanisms for balance.

O*9,02%)*.)R"*#'6520"63F)ID, 451-457

Li X, Aruin AS (2007) The effect of short-term changes in the body mass on anticipatory postural

adjustments. ?/$',"#'012%)R,2"0)K'3'2,65F)EPE, 333-346

Li X, Aruin AS (2009) The effect of short-term changes in body mass distribution on feed-forward

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Massion J (1992) Movement, Posture and Equilibrium - Interaction and Coordination. U,*8,'33) "0)

Y'9,*<"*%*8:F)MP, 35-56

Mochizuki G, Ivanova TD, Garland SJ (2004) Postural muscle activity during bilateral and unilateral

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Nougier V, Teasdale N, Bard C, Fleury R (1999) Modulation of anticipatory postural adjustments in

a reactive and a self-triggered mode in humans. Y'9,*36"'06')V'11',3F)CSD, 109-112

Patla AE, Ishac MG, Winter DA (2002) Anticipatory control of center of mass and joint stability

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Pozzo T, Ouamer M, Gentil C (2001) Simulating mechanical consequences of voluntary movement

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Savelsbergh GJP, Bennett SJ, Angelakopoulos GT, Davids K (2005) Perceptual-motor organization

of children’s catching behaviour under different postural constraints. Y'9,*36"'06')V'11',3F)MJM, 153-158

Shiratori T, Latash ML (2001) Anticipatory postural adjustments during load catching by standing

subjects. A%"0"62%)Y'9,*$5:3"*%*8:F)EEC, 1250-1265

Tijtgat P, Bennett SJ, Savelsbergh GJP, De Clercq D, Lenoir M (2010) Advance knowledge effects on

kinematics of one-handed catching. ?/$',"#'012%)R,2"0)K'3'2,65F)CDE, 875-884

van der Fits IBM, Klip AWJ, van Eykern LA, Hadders-Algra M (1998) Postural adjustments accompanying

fast pointing movements in standing, sitting and lying adults. ?/$',"#'012%)R,2"0)K'3'2,65F)ECD, 202-216

Zago M, McIntyre J, Senot P, Lacquaniti F (2009) Visuo-motor coordination and internal models for

object interception. ?/$',"#'012%)R,2"0)K'3'2,65F)ELC, 571-604

Zattara M, Bouisset S (1988) Posturo-kinetic organization during the early phase of voluntary upper

limb movement .1. Normal Subjects. O*9,02%)*.)Y'9,*%*8:)Y'9,*39,8',:)20()U3:65"21,:F)GE, 956-965

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[ABSTRACT] This study examined if, and how, implicit advance knowledge %4) 23#%!"+6) E*'') 03//7) "+@2/+#/0) *$!) !%8/!/+-0) *+7) *##%!3*+,"+6) 3%0-2$*')adjustments in one-handed catching. Standing subjects were asked to catch balls that were presented with or without implicit advance knowledge of four different ball speeds. Full body kinematics and ground reaction forces were measured, which allowed the assessment of arm movements and postural adjustments through the momentum of the arm, rest of the body and whole body. Providing implicit advance knowledge induced a forward arm raising movement scaled to ball speed in the initial transport phase. However, the accompanying backward postural adjustments were unaffected, which is suggestive of a passive control mechanism. In the subsequent grasping phase, the scaling of arm raising movement exhibited in the presence of implicit advance knowledge resulted in a reduced need for postural adjustments, particularly at the ."6./0-)E*'')03//75)U%6/-./$()-./0/)&+7"+60)0266/0-)-.*-)#%$-"#*')"+8%'8/!/+-)E*0/7)%+)previous experience not only shapes the arm movements but also the subsequent interplaying postural responses.

[KEYWORDS] Implicit advance knowledge; Arm movements; Postural adjustments; Ball catching; Blocked- versus random-order

BASED ON: Tijtgat P, Vanrenterghem J, Bennett SJ, De Clercq D, Savelsbergh GJP, Lenoir M. (2012) Implicit advance knowledge effects on the interplay between arm movements and postural adjustments for catching. Y'9,*36"'06')V'11',3F)GEP,117-121

STUDY 4: IMPLICIT ADVANCE KNOWLEDGE EFFECTS ON THE INTERPLAY BETWEEN ARM MOVEMENTS AND POSTURAL ADJUSTMENTS

IN ONE-HANDED CATCHING

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I!B4D&RX&GF6CGAG!&@4i@;A9&L;E]C94:9&9??9A!I&E;&!H9&G;!9^6C@D&c9!]99;&@^F&FEi9F9;!I&@;4&6EI!B^@C&@4lBI!F9;!I&G;&E;9NH@;494&A@!AHG;:&&

INTRODUCTION

O/3*$*-/)0-27"/0).*8/)0.%1+)-.*-)*78*+#/)9+%1'/76/)"+@2/+#/0)9"+/!*-"#0)%4).*+7)!%8/!/+-0)

(Tijtgat et al. 2010, 2011) as well as postural control mechanisms that enable balance to be maintained

when standing upright (de Lima et al. 2010; Aimola et al. 2011). Advance knowledge in said studies could

be obtained implicitly from the repetition of trials with the same motion characteristics or explicitly by

prior warning. For the control of voluntary upper limb movements such as raising the arm to grasp a cup

or catch a ball, it has been shown that explicit advance knowledge of certain task conditions can facilitate

locally-optimized movement execution, especially when performing under high time pressure (Zago et

al. 2009; Elliott et al. 2010). In reaction-time based arm raising tasks, movement starts earlier and reaches

higher peak velocities with advance knowledge of direction and extent of motion (Rosenbaum 1980;

Mieschke et al. 2001) or target location and impending visual condition (Hansen et al. 2006). Interceptive

actions such as catching differ from these tasks as they are externally-paced and therefore demand that

-./)"+7"8"72*')/0-*E'"0./0)*)03/#"&#)03*-"%-/!3%$*')$/'*-"%+0."3)E/-1//+)-./)*33$%*#."+6)E*'')*+7).*+75)

Still, implicit advance knowledge of ball speed facilitates more scaling of arm kinematics compared to a

more default response exhibited in absence of such prior knowledge (van Donkelaar et al. 1992; Tijtgat

et al. 2010). Similarly, explicit advance knowledge of an upcoming mechanical perturbation (Button et

*'5)IJJIL)%$)8"02*')%##'20"%+)HU":-6*-)/-)*'5)IJRRL)'/*70)-%)*+)*7*3-/7)1$"0-)8/'%#"-,)3$%&'/)*+7)6$*03"+6)

coordination compared to an unexpected situation.

Catching while standing also requires one to establish a suitable postural control in response to

raising the arm upwards and towards the object, as well as controlling postural disequilibrium as a

consequence of the mechanical impulse of the ball acting on the hand (Shiratori and Latash 2001). In

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a related grasping task, it has been shown that implicit advance knowledge of object mass results in a

more forward displacement and earlier peak velocity of centre of pressure for anticipated heavy loads,

as compared to a more default postural response when no such information is available (Aimola et al.

2011). Also, advance knowledge of an impending pendulum-impact with the extended arms at shoulder

level (Santos et al. 2010), or a translation of the support surface with (de Lima et al. 2010) or without

(Horak et al. 1989) an additional supra-postural task, permits a reduction in postural adjustments when

maintaining balance, independent of whether that advance knowledge was obtained implicitly from

blocks of repeated trials or explicitly by prior warnings. At the neural level, consistent temporal coupling

E/-1//+)-./)&$"+6)%4)#%$-"#*')E$*"+)$/6"%+0)*+7)3%0-2$*')$/03%+0/0).*0)E//+)0.%1+)1./+)3*$-"#"3*+-0)

are provided with explicit advance knowledge of a support surface perturbation (Jacobs et al. 2008),

while the absence of advance knowledge of trunk perturbation evoked a large cortical negative potential

that was linked with errors in stability (Adkin et al. 2006).

U%)7*-/()"-)$/!*"+0)2+9+%1+)"4)*+7).%1)*78*+#/)9+%1'/76/)"+@2/+#/0)-./)"+-/$3'*,)E/-1//+)*$!)

!%8/!/+-0)*+7)#%+#%!"-*+-)3%0-2$*')*7:20-!/+-0)4%$)#*-#."+65)O3/#"&#*'',()"-).*0),/-)-%)E/)7/-/$!"+/7)

if the effect of implicit advance knowledge of ball speed on arm movement (i.e., scaling) interacts with

the postural adjustments required to maintain stability during catching. Importantly, high ball speeds

do not only challenge the arm motor system to reach the ball in time, but will also increase demands

on postural control. Based on previous research, we hypothesized that catching with implicit advance

knowledge of ball speed would result in an initial movement impulse of the arm that is more scaled

to ball speed than in the absence of advance knowledge (Tijtgat et al. 2010). Consequently, it can be

expected that the level of postural disturbance when raising the arm and preparing ball-hand impact for

catching would be smaller in the presence of implicit advance knowledge. In combination, this should

result in a diminished need for pronounced postural compensations (de Lima et al. 2010; Santos et al.

2010).

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METHODS

Participants

Six male, self-declared right-handed participants (mean age: 22.4 ± 0.9 years, mean weight 74.9

± 7 kg and mean height 180.3 ± 4 cm) with normal or corrected-to-normal vision gave their written

informed consent for the experiment, which was approved by the Ethical Committee of the host

University.

Apparatus and task

Before each catching trial, participants were asked to remain still in a relaxed standing position

with their feet parallel on a force plate (AMTI, 1000 Hz), arms beside the body with the thumb of

the right hand holding a switch secured to the right thigh, and head upright with gaze located straight

ahead. Participants were instructed to catch yellow, mid-pressured tennis balls that were launched at

a distance of 8.4 m from their frontal plane by a ball-projection machine (Promatch, Mubo B.V.). Balls

1/$/)'*2+#./7)*-)4%2$)03//70)HS5K)!k0()RR5K)!k0()R_5_)!k0)*+7)Rb5j)!k0L)$/02'-"+6)"+)E*'')@"6.-)-"!/0)%4)

896 ms, 737 ms, 629 ms and 532 ms, respectively. The initial height of the ball machine and launch angle

was adjusted so that the balls arrived above the participant’s right shoulder. Spatial standard deviation

of the interception point was 7.84 cm in the medio-lateral, 12.88 cm in the vertical direction and 9.71

cm in the anterior-posterior direction, respectively. A face shield was worn to protect the face, while not

7"0-2$E"+6)*##/00)-%)-./)42'')8"02*')&/'75

Participants attempted to catch a total of 160 balls, delivered in two conditions that differed

according to presentation order (see also Tijtgat et al. 2010). In a blocked-order condition, balls were

delivered in four blocks of 20 trials with the same ball speed repeated. The order of ball speed within a

block was randomly assigned across participants. In a random-order condition, 80 trials were randomly

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I!B4D&R

ordered and delivered in four separate blocks, which each ball speed presented 20 times. Condition

order was counterbalanced across participants. In order to avoid visual anticipation of launching angle,

and hence the ball approach speed, the ball machine was covered with black plastic that had a small

cut-out section through which the balls were released. An opto-electric device was mounted at the

exit of the ball machine to detect the time of ball release. Also, to minimize auditory anticipation of the

moment of ball release, as well as ball speed, participants wore headphones that reduced sound of the

ball machine during ball release. Trials were retaken when the experimenter observed a major deviation

%4)-./)+%$!*')@"6.-)3*-.)H_)m)%4)*'')-$"*'0L5)

Dependent variables and data analysis

Catching performance was evaluated by considering the percentage of successful catches. Kinematic

7*-*)1/$/)#%''/#-/7)20"+6)RI)"+4$*$/7)#*!/$*0)HQ$%$/@/N()r2*'"0,0)MPL5)]*$9/$0)1/$/)3'*#/7)E"'*-/$*'',)

on distal phalanx of hallux and digitus minimus, lateral and medial aspect of calcaneus, lateral and medial

malleolus, lateral and medial femoral condyles, iliac crest, anterior and posterior superior iliac spine,

sternum, C7, intertubercular sulcus of humerus, styloid process of radius and ulna, distal phalanx of

-.2!E)*+7)"+7/N)&+6/$5)M)RKD0/6!/+-)!%7/')#%+0"0-"+6)%4)4//-()0.*+90()-."6.0()3/'8"0()-.%$*Nk*E7%!/+()

upper arms, lower arms and hands was developed using proprietary motion analysis software (Visual

3D, C-motion Inc.).

The onset of arm movement was derived from the forward acceleration of the wrist (i.e., threshold

of 0.5 m/s" was exceeded for at least 50 ms). All trials were temporally realigned with respect to this

onset and were analyzed from 300 ms before to 800 ms after the start of the trial, respectively. From

the full body motion data, anterior-posterior momentum of the right arm (consisting of right upper arm,

lower arm and hand), body without the right arm (rest of body) and body (body) were derived. Peaks in

-./0/)!%!/+-2!)7*-*)1/$/)-./+)"7/+-"&/7)*+7)20/7)*0)7/3/+7/+-)!/*02$/0)%4)3%0-2$*')*7:20-!/+-05)

Also, ground reaction forces (GRF) were expressed relative to their baseline level, taken between 500

and 300 ms before movement onset, and the forward force impulse was calculated.PART II

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For statistical analysis, catching performance scores and the mean data (all trials) per participant for

each dependent variable were submitted to ANOVA with condition (blocked-order, random-order)

and ball speed (9.4, 11.4, 13.3 and 15.8 m/s) as repeated measures. In the case of violations of sphericity,

FD8*'2/0)1/$/)*7:20-/7)1"-.)-./)=$//+.%20/D=/"00/$)3$%#/72$/5)O"6+"&#*+-)!*"+)/44/#-0)%4)E*'')03//7()

*+7)#%+7"-"%+)E,)E*'')03//7)"+-/$*#-"%+0()1/$/)42$-./$)*+*',</7)20"+6)*7:20-/7)'/*0-)0"6+"&#*+-)7"44/$/+#/0)

HBOdL)-/0-05)U./)'/8/')%4)0"6+"&#*+#/)1*0)0/-)*-)p < 0.05.

RESULTS

A main effect of ball speed was evident for catching performance (F3,15

= 16.665, p < 0.001), but

there was no main effect of condition or interaction effect (03). In both the blocked-order and random-

order conditions, catching performance decreased gradually with increasing ball speed (9.4 m/s to 13.3

m/s, p < 0.01; 11.4 m/s to 15.8 m/s, p < 0.05). Participants caught almost all balls at the lowest ball speed

*+7)Tb)m)%4)-./)E*''0)*-)-./)."6./0-)E*'')03//75)

Raising the arm forward for catching (transport phase) resulted in a forward change in momentum

of the arm (Fig. 1a) and, at the same time, a smaller backward change in momentum of the rest of the

body (Fig. 1b). Consequently, the net result was a forward change in momentum of the total body (Fig.

1c). This overall forward momentum change was generated by a forward impulse as observed from

GRF (Fig. 2). Then, in the grasping phase shortly before ball-hand contact (i.e., between 57 ms for the

lowest and 18 ms for the highest ball speed), the arm was moved backward in anticipation of ball impact,

resulting in a backward change in momentum of the arm. This was anticipated by a forward change in

momentum of the rest of the body that was larger than the backward momentum change of the arm at

the higher speeds. The net result of this interplay between postural control for arm raising and grasping

was a sustained forward momentum of the body, primarily at the higher speeds

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I!B4D&R

Figure 1.)Q'20)201',"*,;$*31',"*,)#*#'019#)*.)a)2,#F b),'31)*.)15')<*(:)20()5)<*(:).*,)<%*64'(;*,(',)

d%'.1)$20'%e)20() ,20(*#;*,(',) d,"851)$20'%e) 62165"08)21) 15') .*9,)<2%%) 3$''(3) d0)f)Se=) ]",31) +',1"62%) %"0') "3)

#*#'01)*.)*03'1F)15')*15',)+',1"62%)%"0'3)"0("621')#*#'01)*.)<2%%;520()6*01261)$',)<2%%)3$''( PART II

142

PART IPART IPART IIPART II

Figure 2. Q'20)201',"*,;$*31',"*,)8,*90(),'261"*0).*,6')dHK]e).*,)<%*64'(;*,(',)d%'.1)$20'%e)20(),20(*#;

*,(',)d,"851)$20'%e)62165"08)21)15').*9,)<2%%)3$''(3)d0)f)Se=)]",31)+',1"62%)%"0')"3)#*#'01)*.)*03'1F)15')*15',)

+',1"62%)%"0'3)"0("621')#*#'01)*.)<2%%;520()6*01261)$',)<2%%)3$''(

The mean peaks in anterior-posterior momentum of arm and rest of the body are presented in

a"65)_5)U./$/)1*0)*)0"6+"&#*+-)"+-/$*#-"%+)E/-1//+)#%+7"-"%+)*+7)E*'')03//7)4%$)-./)!*N"!*')4%$1*$7)

momentum of the arm (F1,6

= 5.93, p < 0.05). In the blocked-order condition, the maximal forward

momentum of the arm was smaller at the two lower speeds compared to the two higher speeds (p <

0.05). No change as a function of ball speed was visible for random-order catching (03). The maximal

backward momentum of the rest of the body did not differ over condition or ball speed (03).

A+)-./)6$*03"+6)3.*0/()-./$/)1*0)*)0"6+"&#*+-)!*"+)/44/#-)%4)#%+7"-"%+)HF1,5

= 10.18, p < 0.05) and

ball speed (F3,15

= 6.58, p < 0.01) for the maximal backward momentum of the arm. The backward

momentum was greater for random-order catching than blocked-order catching and for the two higher

speeds compared to the lowest speed (p < 0.05). A main effect of ball speed (F2,9

= 29.52, p < 0.001)

was evident for forward momentum of the rest of the body. Importantly, however, this was superseded

143

I!B4D&R

E,)*)0"6+"&#*+-)"+-/$*#-"%+)E/-1//+)#%+7"-"%+)*+7)E*'')03//7)HF3,15

= 10.64, p < 0.005). At the highest

ball speed, maximal forward momentum was higher for random-order than blocked-order catching (p

< 0.05; see Fig. 1b and Fig. 3b).

Figure 3. Q'20)$'243)"0)#*#'019#)*.)15')2,#)20(),'31)*.)15')<*(:)(9,"08)<%*64'(;*,(',)20(),20(*#;

*,(',) 62165"08)21) 15') .*9,)<2%%) 3$''(3) d0)f)Se=)a)`9,"08)2,#) ,2"3"08F) 2)#2/"#2%) .*,-2,()#*#'019#)*.)

15')2,#)20()#2/"#2%)<264-2,()#*#'019#)*.)15'),'31)*.)15')<*(:) "3)6,'21'(=)b)^.1',)<2%%;520()6*01261F)

2)#2/"#2%)<264-2,()#*#'019#)*.)15')2,#)20()#2/"#2%).*,-2,()#*#'019#)*.)15'),'31)*.)15')<*(:)"3)

6,'21'(=)m)"0("621')3"80"&6201)"01',261"*0)'..'613F #)"0("621')2)3"80"&6201)#2"0)'..'61)<'1-''0)<%*64'(;*,(',)

20(),20(*#;*,(',)d$)n)D=DGo)3''),'39%13)3'61"*0).*,)('12"%3e

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A main effect of ball speed was observed for the resulting maximal forward momentum of the total

body (F3,15

= 9.80, p < 0.005, Fig. 1c). Except for the two highest speeds (03), this maximum increased as

a function of ball speed (p < 0.05). However, the interaction between condition and ball speed did not

$/*#.)0"6+"&#*+#/)H03). Similar effects were observed for the forward force impulse (Fig. 2). There was

a ball speed effect (F1,7

= 16.373, p < 0.005), with a higher forward impulse for the two higher than for

the two lower ball speeds (p < 0.05); and no interaction or condition effect (03).

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DISCUSSION

The aim of the present experiment was to elucidate if, and how, implicit advance knowledge

affects the interplay between arm movements and concomitant postural adjustments for catching. The

present study provides direct evidence that implicit advance knowledge of ball speed facilitates an initial

forward arm raising movement scaled to ball speed. The concomitant postural adjustments during

-."0)&$0-)-$*+03%$-)3.*0/)$/!*"+/7)2+*'-/$/75)A+)-./)'*-/$)6$*03"+6)3.*0/()"!3'"#"-)*78*+#/)9+%1'/76/)

appeared to facilitate a reduced need for postural adjustments, particularly at the highest ball speed.

Therefore we suggest that the observed locally-optimized scaling in the transport phase permitted

less subsequent postural compensation in the grasping phase. The potential underlying mechanisms

/N3'*"+"+6) -./) %E0/$8/7) "+@2/+#/) %4) "!3'"#"-) *78*+#/) 9+%1'/76/) %+) -./) "+-/$3'*,) E/-1//+) *$!)

!%8/!/+-0)*+7)3%0-2$*')*7:20-!/+-0)1"'')E/)7"0#200/7)E/'%1()E2-)&$0-)-./)3$/0/+-)$/02'-0)*$/)$/'*-/7)

-%)3$/8"%20)&+7"+605

Consistent with previous work (Tijtgat et al. 2010), catching performance decreased with increasing

ball speed, but remained equal for both the blocked- and random-order condition. We also found here

that in the transport phase, implicit advance knowledge of ball speed (blocked-order) permitted a

E/--/$)0#*'"+6)%4)*$!)!%8/!/+-)-%)E*'')03//7)H23)-%)Rj)m)"+#$/*0/7)4%$1*$7)!%!/+-2!)4%$)"+#$/*0"+6)

ball speeds, Fig. 3a), compared to a default change in forward arm momentum when trials were

received in random order; for similar results, see Tijtgat et al. (2010). The response by the rest of the

body (maximal backward momentum) was not different between ball speeds during transport, as has

previously been reported for lower ball speeds (Laurent et al. 1994). Importantly, however, while we did

not observe different postural movements between conditions of advance knowledge in the transport

phase, such differences were evident in the grasping phase (Fig. 3). These observations are in agreement

with previous work on reach-to-grasp movements (Aimola et al. 2011), i.e., modulation of postural

adjustments when grasping an object rather than when transporting the arm towards the object. Finally,

-./)&+7"+6)%4)*)0!*''/$)4%$1*$7)!%!/+-2!)%4)-./)$/0-)%4)-./)E%7,)1"-.)"!3'"#"-)*78*+#/)9+%1'/76/)

Ha"65)_EL)#%+&$!0)-.*-)'/00)3$%+%2+#/7)3%0-2$*')$/03%+0/0)-*9/)3'*#/)1./+)-./$/)"0)!%$/)#/$-*"+-,)%4)

PART II

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PART IPART IIPART II

an impending postural perturbation, as has been previously observed for different tasks (de Lima et al.

2010; Santos et al. 2010).

In the transport phase, the observed scaling of arm movement to ball speed when implicit advance

knowledge was provided was not visible in the concomitant postural adjustments (Fig. 3a). Instead, a

default postural response was established in the backward momentum change of the rest of the body.

If anticipatory postural adjustments would be responsible for the control of COM (Aruin and Latash

1995), a momentum of the rest of the body scaled to ball speed would be expected for predictable

perturbations, i.e., when advance knowledge of ball speed is present. However, in contrast to the latter,

current results are more in line with an initial passive control mechanism for balance during standing, as

has been suggested in a previous arm-raising study (Patla et al. 2002). In the ensuing grasping phase, the

E*#91*$7)*$!)!%8/!/+-)1*0)RI)m)0!*''/$)"+)-./)E'%#9/7D%$7/$)-.*+)$*+7%!D%$7/$)#%+7"-"%+)*-)*'')

ball speeds, while the corresponding forward postural change in momentum of the rest of the body was

KR)m)0!*''/$)*-)-./)."6./0-)E*'')03//7)Ha"65)_EL5)A-)0//!0()-./+()-.*-)1./+)-./$/)1*0)*+)"+"-"*')0#*'"+6)-%)

E*'')03//7)-."0)$/02'-/7)"+)*)$/72#/7)+//7)4%$)3%0-2$*')#%+-$%')"+)-./)'*--/$)6$*03"+6)3.*0/5)U./0/)&+7"+60)

support the hypothesis of a reduced postural response when implicit advance knowledge is provided

(de Lima et al. 2002; Pozzo et al. 2002).

Control of momentum when catching while standing requires a central nervous system (CNS)

that enables a functional interplay between the focal component of a task (arm movement) and its

postural adjustments to maintain equilibrium (Pozzo et al. 2002), based on both advance knowledge

and online feedback mechanisms (de Lima et al. 2002). According to Ahmed and Wolpert (2009), such

an interaction could be explained by an inverse mapping for the control of the arm movement and a

forward mapping for the postural responses. Together this allows the CNS to predict the movement

consequences of the catch and to generate an appropriate compensatory control. Evidence for such

distinct control has been found at a neural level by changes in load-related activity of the primary

motor cortex during posture and reaching tasks (Kurtzer et al. 2005). In the transport phase, the default

backward momentum of the rest of the body that occurred irrespective of whether or not there was

a scaled forward momentum of the arm (i.e., with or without advance knowledge of ball speed) is

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I!B4D&R

consistent with the involvement of different mappings between arm movements and postural control.

However, as stated above, such initial postural control is suggested to be a passive control mechanism

(Patla et al. 2002). Therefore, future research through forward dynamic simulations should investigate

whether the initial changes in momentum of the rest of the body are generated by an active control of

the CNS or are merely the consequence of passive postural control.

Together, the observed effects of implicit advance knowledge on the interplay between arm

movement and postural adjustments suggest cortical involvement based on previous experience to

0.*3/)3%0-2$*')$/03%+0/0) "+72#/7)E,)-./)3%0-2$*')3/$-2$E*-"%+0)72$"+6)E*'')#*-#."+65)O3/#"&#*'',() -./)

cerebellar-cortical loop is suggested to be responsible for such postural responses based on prior

experience (Jacobs and Horak 2007). Certainly, some general expectancy of upcoming postural

perturbation will be present in both the blocked-order and the random-order condition. In the random-

order condition, however, this expectancy is likely to be “a best guess about the anticipated postural

perturbation” (Jacobs and Horak 2007, p. 1344), and might be prepared based on the average ball

speed. Such a control mechanism has also been observed in smooth oculomotor control (Bennett et

al. 2006) and path integration (Petzschner et al. 2011). In contrast, implicit advance knowledge of ball

speed in the blocked-order condition allowed the individual to modify postural adjustments on the basis

of prior experience. This prior experience likely informed about the effectiveness of the response to

the recurring perturbation characteristics (Horak et al. 1989). However, it should be acknowledged that

next to cognitive involvement by implicit advance knowledge, a trial-by-trial history effect might also

have contributed to differences in motor control between blocked-order and random-order catching

(Khan et al. 2002; Cheng et al. 2008). In our previous research we tried to minimize these trial-by-trial

adaptations by manipulating vision in a totally random context. We showed that the kinematics of

.*+7)!%8/!/+-0)1/$/)"+@2/+#/7)E,)/N3'"#"-)*78*+#/)9+%1'/76/)HU":-6*-)/-)*'5)IJRRL5)U./$/4%$/()42-2$/)

$/0/*$#.) 0.%2'7) "+8/0-"6*-/) .%1) /N3'"#"-) *78*+#/) 9+%1'/76/) "+@2/+#/0) -./) "+-/$3'*,) E/-1//+) *$!)

movements and postural adjustments in catching

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CONCLUSION

Implicit advance knowledge of the upcoming ball speed resulted in an initial motor response

-.*-)1*0)*7*3-/7)-%)-./)/N3/#-/7)E*'')03//7()"+)#%!E"+*-"%+)1"-.)03/#"&#)3%0-2$*')*7:20-!/+-0)-.*-)

facilitated the motor system to maintain balance in the grasping phase. The absence of such implicit

advance knowledge led to more default initial arm kinematics resulting in a higher postural response

for ball-hand impact under high temporal constraints. This suggests that cortical involvement based on

previous experience does not only shape the arm movements but also the subsequent interplaying

postural adjustments.

ACKNOWLEDGEMENTS

Many thanks to Davy Spiessens for technical support and David Rimbaut and Jacob De Troyer for

their assistance in data collection.

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kinematics of one-handed catching. ?/$',"#'012%)R,2"0)K'3'2,65F)CDE, 875-884

U":-6*-)Q()P/++/--)Oh()O*8/'0E/$6.)=hQ()d/)c'/$#>)d()B/+%"$)])HIJRRL)U%)9+%1)%$)+%-)-%)9+%1X)"+@2/+#/)

of explicit advance knowledge of occlusion on interceptive actions. ?/$',"#'012%)R,2"0)K'3'2,65F)CEI,

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van Donkelaar P, Lee RG, Gellman RS (1992) Control strategies in directing the hand to moving

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Zago M, McIntyre J, Senot P, Lacquaniti F (2009) Visuo-motor coordination and internal models for

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6@^!&PX

:9;9^@C&4GIABIIGE;

U./)32$3%0/)%4)-./)3$/0/+-)-./0"0)1*0)-%)0-27,)-./)"+@2/+#/)%4)*78*+#/)9+%1'/76/)on hand and arm kinematics, and concomitant postural adjustments, when catching a ball. A close perception-action coupling between visual information and the corre-sponding motor output during interceptive actions has been well documented in pre-vious research. However, the role of advance knowledge in the control of these visu-ally guided actions was often overlooked. Therefore, the role of implicit (study 1) and explicit (study 2) advance knowledge was studied in two ball catching experiments. Next, postural adjustments that accompany catching were scrutinized in a pilot study H0-27,)_L()4%''%1/7)E,)*+)"+8/0-"6*-"%+)%4).%1)3%0-2$*')*7:20-!/+-0)*$/)"+@2/+#/7)E,)implicit advance knowledge (study 4). Section 1 of this general discussion overviews -./)!*"+)$/0/*$#.)&+7"+605) A+)0/#-"%+)I)-./0/)&+7"+60)*$/)7"0#200/7)1"-.)$/4/$/+#/)-%)$/#/+-)$/0/*$#.)&+7"+60)%+)*78*+#/)9+%1'/76/)"+).2!*+)!%-%$)#%+-$%'5)O/#-"%+)3 derives some theoretical considerations from the established effects of advance knowledge. Neuronal substrates that are important for catching are highlighted in section 4, together with suggestions of how advance knowledge might manifest in the brain. Section 5 considers the strengths and limitations of the present research. Finally, some practical implications and future directions are suggested in section 6.

GENERAL DISCUSSION

PART III

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PART IIIPART III

78% 9-22".:%+4%,;'%2")3%.'#'".(;%*30)3<#

The experimental studies in this thesis attempted to identify if, and how, advance knowledge

"+@2/+#/0)-./)/N/#2-"%+)%4)*)4*0-)"+-/$#/3-"8/)#*-#."+6)-*095)a$%!)*)0-*+7"+6)3%0"-"%+()3*$-"#"3*+-0)1/$/)

asked to catch tennis balls projected at their right shoulder while task conditions were either varied

4$%!)-$"*'D-%D-$"*')%$)$/3/*-/7)0/8/$*')-"!/05)A+)*)&$0-)/N3/$"!/+-)H0-27,)RL()02##/0042')#*-#./0)%4)E*''0)

delivered in four blocks of the same ball speed were compared to those in which the ball speed varied

randomly between trials. Catching in blocks of the same ball speed yielded a different motor response

compared with catching balls that were delivered with a random-ordered ball speed. Having initiated

the movement earlier and with a greater magnitude of initial wrist velocity, participants moved with a

less rectilinear hand path in the random-order condition than the blocked-order condition at the lowest

ball speed. This provided a longer movement time and thus a larger temporal window to negotiate

the unexpected temporal constraint on-line. Based on implicit advance knowledge gathered through

3$/8"%20) -$"*'0() -./) "+"-"*')1$"0-) 8/'%#"-,) 3$%&'/)1*0)!%$/) 0#*'/7) -%) E*'') 03//7) "+) -./) E'%#9/7D%$7/$)

condition.

a$%!)-."0)&$0-)0-27,)"-)#%2'7)+%-)E/)7/-/$!"+/7)1./-./$)-./)"+@2/+#/)%4)*78*+#/)9+%1'/76/)%+)

interceptive behaviour was merely a consequence of ‘cognitively impenetrable’ trial-by-trial adaptations

(de Lussanet et al. 2002; Song and Nakayama 2007), or the expression of conscious expectations

regarding the upcoming trials (Zelaznik et al. 1983). Therefore, a second experiment (study 2) was

designed with a complete random-order design that enabled trial-by-trial adaptations to be minimized.

Trials in which early, late or no occlusion were announced a priori were compared to trials without

such explicit advance knowledge. Explicit advance knowledge of visual occlusion resulted in a limb

transport, adapted to the particular occlusion conditions, together with an increased grasping time. In

the unexpected condition, visual occlusion resulted in a higher peak of wrist velocity to give increased

opportunities to overcome an uncertain situation.

:9;9^@C&4GIABIIGE;

157

Next to differences in the kinematics of the reaching and grasping movement, it was our objective

to scrutinize whether advance knowledge would additionally have an impact on the postural control

for catching. Before attempting to answer this question, a pilot study with a descriptive analysis of

the postural adjustments for catching was deemed appropriate (study 3). A combination of full-body

kinematics, kinetics and postural muscle activity was conducted to scrutinize what postural adjustments

manifest during catching and how they relate to, or differ from, a well-studied (reaction-time) arm-

raising task. It was shown that raising the arm indeed differed between the reaction-time and the

#*-#."+6) -*09()1"-.) *)!%$/) @/N/7)/'E%1) 4%$) -./) '*--/$) -.*-) $/02'-/7) "+) '/00) />2"'"E$"2!)7"0-2$E*+#/5)

Consequently, an ankle strategy in accord with an inverted pendulum mechanism was found to be the

predominant postural strategy as compared to an additional counter-rotating mechanism at hip level

for reaction-time arm raising.

A+)*)&+*')/N3/$"!/+-)H0-27,)KL()-./)/N3/$"!/+-*')7/0"6+)%4)0-27,)R)1*0)$/3'"#*-/7()-."0)-"!/)1"-.)

full-body kinematics and kinetics to allow an investigation of the postural adjustments for catching

with or without advance knowledge of ball speed. It was shown that advance knowledge not only has

*+) "+@2/+#/)%+)-./) "+"-"*').*+7)!%8/!/+-()E2-)*'0%)*44/#-0)-./)3%0-2$*')*7:20-!/+-0) "+72#/7)E,)-./)

backwards arm movement around ball-hand impact.

c'/*$',) -./+() #2$$/+-) 0-27"/0) 0.%1) -.*-)*78*+#/)9+%1'/76/) "+@2/+#/0)!%8/!/+-)E/.*8"%2$) 4%$)

%+/D.*+7/7)#*-#."+65)A+)-./)+/N-)0/#-"%+()-./0/)&+7"+60)*$/)$/'*-/7)-%)$/#/+-)/N3/$"!/+-0)%+)*78*+#/)

knowledge.

PART III

158

PART IIIPART IIIPART III

=8% >-.,;'.%.'#'".(;%#-&&+.,%(+3*.2)3<%,;'%'44'(,%+4%"0?"3('%knowledge

^#5#,*& 8+K8,5#)#,*$& %,& %,*#15#J*%K#& "%**%,3_& 58*5"%,3_& 8,+& J0$*'18.& 50,*10.& *8$S$&

J10K%+%,3&-'1*"#1&$'JJ01*&*0&*"#&"7J0*"#$%$&0-&8+K8,5#&S,0T.#+3#&#--#5*$&%,&*"#&3'%+8,5#&

0-&%,*#15#J*%K#&(#"8K%0'1_&81#&0K#1K%#T#+&8,+&1#.8*#+&*0&*"#&5'11#,*&/,+%,3$M

A+)$/#/+-),/*$0()-./)"+-/$/0-)%4)-./)3%00"E'/)"+@2/+#/)%4)*78*+#/)9+%1'/76/).*0)"+03"$/7)$/0/*$#.)

on interceptive behaviour. Especially for fast interceptive hitting actions, the role of advance knowledge

in the form of feedforward control is the suggested control strategy for these actions (Tresilian 2004).

Indeed, advance knowledge of target velocity (decrease or not) has been shown to vary movement

time, depending on situational probability (Neto and Teixeira 2009, 2011), although timing adjustments

were still required on the basis of current visual information. In a similar vein, advance knowledge of the

required interception zone facilitated advance preparation of the motor response, resulting in greater

03*-"*') *##2$*#,) H]*$"+%8"#) /-) *'5) IJJj() IJRJL5)U./0/) &+7"+60) 0233%$-) -./) +%-"%+) %4) *) 4//74%$1*$7)

control strategy instead of (for movement times below 200 ms; van Soest et al. 2010), or in addition

to, a feedback strategy by continuous visual information under high temporal constraints. The current

&+7"+60) %+) #*-#."+6) 0.%1/7) -.*-) *78*+#/) 9+%1'/76/) #*+) *'0%) "+@2/+#/)!%8/!/+-) E/.*8"%2$) 4%$)

slower movements. Interestingly, it has recently been suggested that a goal keeper should not only rely

%+)"+0-*+-*+/%20)8"02*')E*'')@"6.-)"+4%$!*-"%+()E2-)*'0%)0.%2'7)-*9/)"+-%)*##%2+-)-./)-%DE/D3/$4%$!/7)

action (i.e., advance knowledge based on expectations) in deciding when to start moving (Dessing and

Craig 2010). Especially for spin-induced lateral ball acceleration, a trade-off emerges between waiting

longer to observe more of the ball trajectory and starting to move earlier in order to reach the correct

position in time to stop the ball. Delaying movement initiation, as observed by more experienced goal-

keepers, could compensate for the limited sensitivity to spin-induced visual accelerations. Together, these

$/02'-0)#%+&$!)*+)/44/#-)%4)*78*+#/)9+%1'/76/)%+)"+-/$#/3-"8/)E/.*8"%2$()*+)"+@2/+#/)-.*-)!"6.-)E/) :9;9^@C&4GIABIIGE;

159

subtle and might not always be detectable by performance differences (see equal performance in the

current studies). Indeed, kinematic changes better illustrate different control strategies with or without

advance knowledge.

M-)-./)'/8/')%4)3%0-2$*')*7:20-!/+-0()-./)"+@2/+#/)%4)*78*+#/)9+%1'/76/)%+)3%0-2$*')#%+-$%').*0)

recently been evidenced for grasping objects of different mass (Aimola et al. 2011), and for keeping

balance during body perturbations due to an impact at shoulder level (Santos et al. 2010), as well as by

translating the support surface while keeping a cylinder balancing on a plate (de Lima et al. 2010). For

ball catching, studies that directly measured postural adjustments are scarce. A previous experiment on

ball catching reported that postural adjustments were absent over changing ball speeds that appeared in

blocked-order (Laurent et al. 1994). This contrasts with the increasing postural adjustments for increasing

ball speeds that were observed in study 4 of the current thesis. The discrepancy might be explained by

the low ball speeds (ranging from 5.7 to 9.0 m/s) in the study of Laurent et al. (1994). When further

increasing these ball speeds, e.g., up to 15.8 m/s as in study 4, changes in postural adjustments could have

appeared as well. Interestingly, however, in study 4, it was also observed that at this highest ball speed,

3%0-2$*')*7:20-!/+-0)*$%2+7)E*''D.*+7)#%+-*#-)1/$/)*77"-"%+*'',)"+@2/+#/7)E,)*78*+#/)9+%1'/76/)%4)

upcoming ball speed.

PART III

160

PART IIIPART III

3. Theoretical perspective

!"%$& $#5*%0,& 50,$%+#1$& $0)#& *"#01#*%58.& %,*#1J1#*8*%0,$& 0-& *"#& #)J%1%58.& /,+%,3$M&

!"#&#--#5*&0-&8+K8,5#&S,0T.#+3#&*"8*&T8$&0($#1K#+&%,&*"#&J1#$#,*&*"#$%$& %$& -18)#+&%,&

$#K#18.&+%--#1#,*&J"%.0$0J"%58.&8JJ1085"#$_&18,3%,3&-10)&,0,N1#J1#$#,*8*%0,8._&#50.03%58.&

%,*#,*%0,8.& $2'%1*$& 0,& *"#&)0K#)#,*& $7$*#)& *0& J1%01$& %,& "%3".7& 50)J'*8*%0,8.& ,#'18.&

,#*T01S$M&@.*"0'3"&*"#&J1#$#,*&*"#$%$&+%+&,0*&%,*#,+&,01&8..0T&50,/1)8*%0,&01&-8.$%/58*%0,&

0-&*"#$#&)0*01&50,*10.&*"#01%#$_&*"#&J1#$#,*&1#$#815"&/,+%,3$&#)J"8$%[#&*"8*&8+K8,5#&

S,0T.#+3#&58,&85*&8$&8&503,%*%K#&)#+%8*01&+'1%,3&%,*#15#J*%K#&85*%0,$&$'5"&8$&58*5"%,3M&

The study of interceptive actions has a long tradition of theoretical backgrounds that are oriented

between ecological and cognitive approaches (see Box 1). This section discusses how the role of advance

knowledge can be somehow incorporated in the most recent developments of both spectra.

Since a stringent ecological approach has a strong non-representational premise that is hardly

mediated by cognitive processes (Gibson 1979; Michaels and Carello 1981; Fajen et al. 2009; Box 1),

advance knowledge, as non-instantaneous information source mediated by cognition, was believed to

have no action consequences (Michaels 2000). This statement is hard to unify with the present research

&+7"+605)Y/3$/0/+-*-"%+0)*$/)"7/+-"&*E'/)*03/#-0)%4)"++/$)3$%#/00"+6)1.%0/)42+#-"%+*')$%'/)"0)-%)t0-*+7D

in’ for environmental, individual or task constraints (Clark 1997) so that it can guide behaviour in the

absence of instantaneous information (Warren 2006) or under high time pressure. While full-blooded

"+-/$+*')$/3$/0/+-*-"%+0)1"'')3/$.*30)+/8/$)&-)"+)-./)3."'%0%3."#*')4$*!/1%$9)%4)-./)/#%'%6"#*')*33$%*#.)

(see Stepp and Turvey 2010 for recent non-representational alternatives), subjective representations

that facilitate rather than determine motor behaviour (Reed 1992, see also Laurent and Ripoll 2009),

can come into play, for example, when a subject is warned that an early occlusion will occur during his :9;9^@C&4GIABIIGE;

161

catching movement (study 2). This does not mean that the exact period of visual occlusion of the ball is

estimated (objective representation), but rather that an ‘indexical’ representation is formed (Agre 1995).

In a similar vein, suggesting that some kind of an internal representation can guide interception, does

not necessarily mean that this representation implies a high cognitive contribution (with explicit, analytic

knowledge of the world), but might equally likely represent not more than an implicit approximation

of the task that is implemented in some analogue neural circuit (Zago et al. 2008, 2009; see also Clark

1998; Lopez-Moliner et al. 2007).

From a dynamical system perspective1, movement behaviour under different conditions (e.g., ball

03//7L)3$/0/+-/7)"+)E'%#9/7D%$7/$)#*+)E/)*--$"E2-/7)*0)*)&N/7)*--$*#-%$)%4)#%+7"-"%+)H?*!*!%-%)*+7)

Gohara, 2000). In contrast, the absence of advance knowledge (random-order condition) has been

modelled as a dynamical system with fractal transitions between the excited attractors. Doing so, an

alternative mathematical explanation is prompted for a strategy-based movement outcome based on

cognition. However, a strict dynamical system cannot explain how a movement system starts off with

a given attractor state. In contrast, an alternative view on dynamical systems in the ecological approach

has allowed cognition (by intentions) to play a role in movement behaviour (Davids et al. 2001a).

Empirical evidence very close to our results (different responses with advance knowledge of wrist

perturbation during catching) were described as a squirt of intentional information (Button et al. 2000)

and anticipatory strategy (Button et al. 2002) that come across the intrinsic dynamics of the catching

movement. Thus, intentions based on advance knowledge of a certain perturbation can override the

coordination patterns that are prominent, and guide the dynamical system of a catching movement

(Davids and Button 2000).

Finally, recent advancements in sports psychology research attempted to integrate aspects of

-./)/#%'%6"#*')*33$%*#.)1"-.)."6./$D'/8/')#%6+"-"8/)3$%#/00/0) '"9/)7/#"0"%+D!*9"+6)Hf"--)*+7)Q$%4&--)

2008; Raab et al. 2009; Laurent and Ripoll 2009; Nitsch 2009). For example, expert rugby players

judged the possibility to pass between two defenders in rugby not only by a tau-differential variable

H7"$/#-)3/$#/3-"%+D*#-"%+)#%23'"+6[)0//)Q*$-)R()P%N)RL()E2-)1/$/)*'0%)"+@2/+#/7)E,)*+-"#"3*-/7()$26E,D

03/#"&#)*#-"%+)#*3*E"'"-"/0()"5/5()E*0/7)%+)*78*+#/)9+%1'/76/)Hc$*"6)*+7)f*-0%+)IJRRL5)c$2#"*')4%$)-./0/)PART III

162

PART IIIPART III

developments is the notion that the well-known perception-action cycle (see Fig. 1) is extended to

higher-level cognitive processes so that the multiple coupling between action, perception and cognition

is acknowledged. However, it is stressed that simple heuristics (Raab et al. 2009) and ‘teleological’

constraints (Laurent and Ripoll 2009) enable a cognitive involvement in parsimonious way without the

burden of a high computational load.

Figure 1. @5')$',6'$1"*0;261"*0) 6:6%')20() 15')'#<*("#'01)*.) 6*80"1"*0)23)20) "0("+"(92%) 6*031,2"01) *0)

$',6'$1"*0)d^(2$1'().,*#)V29,'01)20()K"$*%%)CDDLe)

1 Dynamical systems are often considered as a study vehicle for ecological psychologists. See Beek et al. (1995) for an insightful introduction of the concepts of the dynamical systems approach and its interrelationship with the ecological approach.

:9;9^@C&4GIABIIGE;

163

A+) #%+#'20"%+() *'-.%26.) -./) /#%'%6"#*') *33$%*#.) "0) $"6.-42'',) #*2-"%20) %4) 023/$@2%20) #%6+"-"8/)

*33$%N"!*-"%+0)-.*-)#*+)E/)0%'8/7)*'-/$+*-"8/',()-./)1*,)*78*+#/)9+%1'/76/).*0)0.%1+)"-0)"+@2/+#/)%+)

movement behaviour does not seem at odds with recent considerations of this perspective.

g!8S%,3&%,*0&8550',*&8&J1%01%&S,0T.#+3#&)%3"*&(#&S#7&*0&T%,,%,3&8&*#,,%$&)8*5"Mh&

_*,("08)20()B*%$',1)dCDDIeF)$=)CIS=

From a computational perspective, catching a ball entails the generation of a complete internal

model based on a full-blown representation of the individual, task and environmental constraints; and

its interactions (Wolpert and Ghahramani 2000; Todorov 2004; Pezzulo 2008; Brown et al. 2011). Since

these models aim at an improvement of the estimates of the physical world to act upon, advance

knowledge of ball speed (study 1 and 4) or occlusion (study 2) can serve as a facilitator (or ‘prior’) of

the interceptive behaviour. The absence of advance knowledge invokes an optimization strategy that

reckons with the uncertainty of ball speed or occlusion (see Elliott et al. 2010 for a similar approach on

6%*'D7"$/#-/7)*"!"+6L5)U./)3$/0/+-)&+7"+60()*0)1/'')*0)3$/8"%20)/N3/$"!/+-0)H;*+0/+)/-)*'5)IJJT[)d*2!)

et al. 2007), showed that in such an uncertain situation, the human system prepares a default response,

based on an best-bet estimate of the different task probabilities.

PART III

164

PART IIIPART III

BOX 1. ON THE ECOLOGICAL-COGNITIVE DISSOCIATION

AND ATTEMPTS AT RECONCILIATION

@A,%)#%,;'%,;'+.:%,;",%0'()0'#%B;",%B'%("3%*308C ^%<',1)?"031'"0)dELCSe)b9*1'()<:)!5',"(20)dELPPe)$=)EGJ=

The dichotomy between the ecological and cognitive (also referred to as constructivist, computational or information-theoretical) perspective originates from the philosophical discussion whether the human brain makes inference of the world (cognitive) or perceives the world directly to act upon (ecological). Both approaches consider the skill of ball catching in a different way. According to the ecological perspective, the sensory stimuli (light of the ball) derived from the environment are #%+0"7/$/7)024&#"/+-)"+)+*-2$*')#%+7"-"%+0)0%)-.*-)%3-"#*')"+8*$"*+-0)H4%$)/N*!3'/)-*2()0//)Q*$-)R()P%N)1) can be detected directly, without the need of representation. In contrast, according to the cognitive perspective, light of the ball is projected on the retina and the human brain quickly computes what is being seen (the ball) and how it will reach the hand from a perceived direction and velocity. This information is fed into a planning system, which holds a detailed representation of the task that might incorporate advance knowledge such as presented in the present experiments. The planning systems further infers what needs to be done by the motor system, i.e., get the hand at the right time at the right place and starting the grasp early enough taking into account the postural adjustments needed for arm raising and ball-hand impact (based on van Gelder and Port 1995).

While the fundamentally different underlying philosophical assumptions of both approaches !"6.-).*!3/$) "+-/6$*-"%+) -%1*$70)*)2+"&/7) -./%$,()1/)3$/4/$)*)3$*#-"#*') $/*'"0!) -.*-)*--/!3-0)*)reconciliation (see also Rosenbaum 1991; Summers 1992; Abernethy et al. 1994; Clark 1998; Davids et al. 2001a; Norman 2002; Shumway-Cook and Woollacott 2012). Interestingly, at a certain level of analysis, the similarities seem greater than the differences (Anson et al. 2005) so that much of the confusion might be more about terminology than about real fundamental differences. While emphasizing the differences between the two approaches (and the models in between) maintains a fruitful debate, it remains also realistic to adhere a global perspective that does not exclude one of both approaches. Otherwise, if ecological psychologists prefer to maintain their radical non-representational position, their future research should investigate how cognitive interventions (such as advance knowledge effects) interact with the direct perception-action coupling (see also Buekers 2000), instead of adhering to domains of study in which suitable ambient environmental stimuli exist that might substitute representations (Clark and Toribio 1994).

:9;9^@C&4GIABIIGE;

165

In the two visual systems model of Milner and Goodale (1995, 2008), aspects of the ecological and

computational approach are conceptualized by two separate visual cortical pathways (see also Norman

2002). The visual system is thought to comprise a dorsal visual pathway responsible for visuo-motor

behaviour (the action system), and a ventral visual pathway that enables a representation of the world

H-./)3/$#/3-"%+)0,0-/!L5)M'-.%26.)#*-#."+6)"0)#*-/6%$"</7)!*"+',)2+7/$)-./)"+@2/+#/)%4)7%$0*')0-$/*!)

processes, the interacting contribution of the ventral system has been emphasized for interceptive

behaviour (van der Kamp et al. 2008). A few hundreds of milliseconds around movement onset, a

3*$*''/')#%+-$"E2-"%+)%4)-./)7%$0*')*+7)8/+-$*')0,0-/!)"0)0266/0-/7()1."#.)!*,)/N3'*"+)-./)"+@2/+#/)%4)

advance knowledge of ball speed on the initial movement outcome (see study 1 and 4). The scaled

"+"-"*')1$"0-)8/'%#"-,)3$%&'/)"0)-./+)*--$"E2-/7)-%)*+)*77"-"%+*')"+@2/+#/)%4)-./)8/+-$*')0,0-/!()"5/5()8"02*')

information of ball speed that has previously been encountered (Norman 2002). However, over longer

time periods than just the imminent trial, many other reciprocal interacting cortical areas in the ventral

area are suggested to come into play (Green 2001), as well as brain processes that are not directly

related to visual processing, as will be highlighted in section 4.

Admittedly, the current results do not permit to decide one to determine whether one theory is

more suitable than the other at explaining visuomotor behaviour. Whether a catching movement is built

on a detailed (or full-blooded) internal model or not, remains an open question for future research.

However, these and other recent results (see section 2) add to the knowledge that ‘some kind of

representation’ of an intended effect precedes the action. Otherwise, specifying a goal-satisfying motor

pattern seems impossible (Kunde et al. 2007; Clark and Toribio 1994). Such a representation before

movement onset permits the nervous system to take a head start over motor control processes

that depend exclusively on instantaneous sensory information (Elliott 2008). Importantly, the observed

advance knowledge effects do not exclude the idea that the instantaneous (visual) information is

*7/>2*-/) -%) 3/$4%$!) 02##/0042'',5) ;%1/8/$() :20-) E/#*20/) -."0) %3-"#*') "+4%$!*-"%+) "0) 024&#"/+-) 7%/0)

not mean that advance knowledge cannot be also informative for perception-action coupling (Witt

*+7)Q$%4&--)IJJjL5)c'/*$',()-./+()*78*+#/)9+%1'/76/)%4)-*09)3*$*!/-/$0)#%2'7)*"7)*)E/--/$D7/8/'%3/7)PART III

166

PART IIIPART III

representation, leading to a different movement outcome. The present results suggest that cognitive

involvement other than instantaneous visual information processing plays a role in the neural circuitry

responsible for interceptive actions (see also Neto and Teixeira 2009), making explicit the interplay

between cognition, perception and action (see Part 1, Section 3; Shumway-Cook and Woollacott 2012).

In the next section, candidate neural substrates during catching and those brain structures responsible

for advance knowledge are discussed.

:9;9^@C&4GIABIIGE;

167

4. Catching in the brain and neural evidence for advance knowledge

G,&$*'+7%,3&)0*01&(#"8K%0'1_&*"#&310T%,3&%)J01*8,5#&0-&,#'18.&$'($*18*#$&*"8*&$'JJ01*&

*"#&#)J%1%58.&/,+%,3$&0-&J$75"0.03%58.&50,$*1'5*$&$"0'.+&,0*&(#&+%$1#381+#+&dL#%.&#*&8.M&

<===eM&!"%$&$#5*%0,&0K#1K%#T$&$0)#&,#'18.&$*1'5*'1#$&*"8*&81#&%)J01*8,*&-01&58*5"%,3&8,+&

)0+#$*.7&8**#)J*$&*0&',+#1$*8,+&*"#&J1#$#,*&8+K8,5#&S,0T.#+3#&#--#5*$&%,&*"#&.%3"*&0-&

1#5#,*&8+K8,5#)#,*$&%,&,#'10$5%#,5#M

Most parts of the human brain are somehow involved in the execution of even the simplest

!%8/!/+-() ./+#/) "+7"#*-"+6) -.%0/) 03/#"&#) E$*"+) $/6"%+0) *+7) 3$%#/00/0) -.*-) #%+&$!) -./) 8*'"7"-,) %4)

advance knowledge for catching, seems a tough nut to crack. Next to the differentiation of particular

brain locations during catching (typically measured with functional magnetic resonance imaging - fMRI),

the activation of brain potentials over different time scales (measured through electroencephalography

- EEG; or magnetencephalography - MEG) are considered (for a recent overview of functional

neuroimaging, see Friston 2009). From a different perspective, the brain is approached as a statistical

inference machine through which individual neuronal interactions between different levels are modelled.

(Friston 2005; see also Box 2). We will try to illustrate how these different approaches can be applied to

the case of ball catching and present some suggestions of particular differences that might come across

when catching with or without advance knowledge.

Catching demands at least some anticipatory control (see Part 1, section 1) that involves many different

brain regions (Fig. 2). Three different types of anticipatory slow brain potentials (i.e., electrophysiological

changes) generated in the cerebral cortex are suggested to precede the actual catching movement: the

readiness potential (RP), the contingent negative variation (CNV) and the stimulus-preceding negativity PART III

168

PART IIIPART III

(SPN). These potentials slowly increase negative shifts up to the release of the ball (for a detailed recent

overview, see Brunia et al. 2011). Although this suggests that several anticipatory brain processes occur

prior to a catching action, it should be noted that these brain potentials are extrapolations based on

other tasks that have not yet been tested separately in a real catching situation2. The RP refers to the

readiness in preparation of the execution of the (catching) movement. The motor cortex, primary

somatosensory cortex, the premotor cortex and motor areas in the frontal cortex are activated

during the generation of the RP. CNV is evident if a warning stimulus (i.e., raising the thumb of the

experimenter that introduced the future ball launch) announces that an imperative stimulus (i.e., the

visual appearance of the ball) will arrive. This form of anticipatory attention is present over all brain

areas that are involved in the upcoming catching task, i.e., both movement- and perception-related. The

OQW)"0)*)+%+D!%-%$)*+-"#"3*-%$,)0'%1)1*8/)-.*-)/!/$6/0)03/#"&#*'',)1./+)1*"-"+6)4%$)-./)0-"!2'20()"5/5()

-./)E*''()-%)*33/*$5)OQW)#*+)E/)7"44/$/+-"*-/7)E,)*)!%7*'"-,D03/#"&#)1*8/)"+)-./)%##"3"-*')E$*"+)*$/*0)

prior to the visual appearance of the ball; a wave in the frontal cortex related to anticipation of the

information content of the stimulus (importantly, a possible effect of advance knowledge could be

expected for this wave); and a wave in the insular cortex for emotional anticipation (van Boxtel and

Bocker 2004). However, a catching task complicates a clear distinction between the preparation of the

voluntary movement and the preparedness or expectation of the upcoming ball. Only few experiments

on interception tasks have investigated how brain potentials evolve prior to a catching movement. Thus,

changes in electroencephalographic rhythms in supplementary motor, premotor and prefrontal areas

were only vaguely associated to $%200"08)20()$,'$2,21"*0 in a two-dimensional catching task (Tombini et

al. 2009). Likewise, when waiting for the ball to fall, activity in the posterior parietal cortex was related

to expectancy, planning and preparedness for the anticipated grasp in catching (Nader et al. 2008), and

activation of the frontal cortex was related to '/$'6121"*0F)$%200"08)20()#*1*,)$,'$2,21"*0 (Portella et al.

2007; Velasques et al. 2007; Machado et al. 2008).

2 A distinction between different cortical slow waves was possible by different experimental contexts such as self-paced or reaction time button-press tasks with or without warning stimuli and knowledge of results tasks (Brunia et al. 2011).

:9;9^@C&4GIABIIGE;

169

Figure 2. @5')$,'("61"+')<,2"0=)!"#$%"&'(),'$,'3'0121"*0)*.)<,2"0)2,'23)1521)52+')<''0)233*6"21'()-"15)

3*#')23$'613)*.)$,'("61"*0=)d^(2$1'().,*#)R9<"6)'1)2%=)CDEDe)

As catching is suggested to be grounded on an interplay between perception, action and cognition

(see Part 1, section 2), cortical motor areas are likely to receive crucial information from sensory

association and prefrontal areas that integrate current sensory information with stored knowledge

(Ghez and Krakauer 2000). Regarding the association of the motor process and sensory information,

the activation of neuronal clusters in the primary motor cortex of rhesus monkeys showed a parallel

processing of target information and the generation of hand movements during interception (Port et

al. 2001). Accordingly, when catching a free-falling ball, neural networks of humans were activated in the

motor cortex and extending to the somatosensory cortex (Fautrelle et al. 2011). Two separate visual

cortical pathways have been presented in the visual cortex of primates (Milner and Goodale 1995): a PART III

170

PART IIIPART III

ventral (perception) stream projecting to the inferotemporal cortex and a fast dorsal stream for action

projecting to the posterior parietal cortex that is mainly activated for catching movements (Senot et al.

2008), but see the possible ventral contribution to catching in section 3 (van der Kamp et al. 2008). Also,

the posterior parietal cortex and the middle superior temporal areas have been designated as the neural

representation of tau (see Part 1, Box 1; Merchant and Georgopoulos 2006). The premotor cortex is

suggested to play a crucial role by the manifestation of a “multi-purpose and multi-component bridge

between perception and action: action goals, provided by the external environment and suggested by

"+-/$+*')7$"8/0()*$/)03/#"&/7)"+)3*$*!/-/$0)-.*-)#*+)E/)7"$/#-',)3*00/7)-%)-./)!%-%$)/44/#-%$0()*+7)&+*'',)

re-enter the perception-action circle” (Schubotz 2004, p. 91). During latency, a comparison is suggested

between elements pre-stored in the frontal (i.e., implicit memory) and somatomotor cortex and new

parameters of the upcoming motor action (Portella et al. 2007; Machado et al. 2008). Therefore, it is

tempting to suggest that implicit advance knowledge through repetition (e.g., blocked-order catching,

0-27,)R)*+7)KL()!"6.-)3'*,)*+)"+@2/+-"*')$%'/)"+)-."0)#%!3*$"0%+5)A+)*77"-"%+()!%-%$)*$/*0)"+)-./)#%$-/N)

are modulated by subcortical structures such as the cerebellum (Ghez and Krakauer 2000). Indeed,

the effects of cerebellar damage (Lang and Bastian 1999; Bastian 2006) and the activation of this brain

region during catching (Fautrelle et al. 2011) have shown that the cerebellum has a pivotal role in the

control of catching.

Since there exist different ways to conceptualize and differentiate the role of the referred brain areas,

a critical note on these type of brain activation and localisation studies is that the type of processing is

+%-)*'1*,0)#'/*$',)03/#"&/7)HP2E"#)/-)*'5)IJRJL5)M'0%()1./-./$)-./)%E0/$8/7)E$*"+)*#-"8*-"%+)"+)#%6+"-"8/)

areas resonates an essential characteristic of brain organization during the action, or merely expresses

an epiphenomena stemming from discrete modular processes, is a future avenue for neurophysiological

$/0/*$#.)HO%+6)*+7)W*9*,*!*)IJJSL5)W/8/$-./'/00()+/2$%'%6"#*')&+7"+60)32-)/!3.*0"0)%+)#%6+"-"%+)

as an important mediator of the individual constraints introduced in the general introduction (see

Part 1, section 2). Catching a ball seems to result in certain expectancies of the task so that cognitive

involvement cannot be excluded, in contrast to previous claims that no (Michaels 2000; Michaels et al. :9;9^@C&4GIABIIGE;

171

2001) or only very moderate (de Lussanet et al. 2002; Song and Nakayama 2007; Whitwell et al. 2008;

Whitwell and Goodale 2009) cognitive involvement would guide such actions.

U.*-)-./0/)/N3/#-*+#"/0)*$/)!/7"*-/7)E,)03/#"&#)*78*+#/)9+%1'/76/)%4)-./)-*09)#%+0-$*"+-0).*0)

only recently been evidenced by the activation of additional neural networks in the supplementary

motor area, the premotor cortex and the left posterior cerebellum, when subjects caught balls with

a random weight (Fautrelle et al. 2011) as compared to a blocked-order condition. Increased brain

activation was visible when catching in an uncertain situation, such as random or if vision was occluded.

The activation in the left occipito-temporal cortex in the unexpected situation was attributed to

an increased engagement of visual attentional resources. This observation is in agreement with the

subjective reports of eight (out of twenty) subjects in study 2 that unexpected condition required

increased preparedness.

A recent neurophysiological level of analysis scrutinizes the role of prior expectations in sequential

reaching by modelling individual neuronal dynamical interactions over different parts of the brain

Ha$"0-%+)/-)*'5)IJRJL5)O2#.)3$"%$)/N3/#-*-"%+0)1"'')%E8"%20',)E/) "+@2/+#/7)E,)*78*+#/)9+%1'/76/)%4)

task constraints, thus greater evoked responses of dopamine could be expected (Friston et al. under

revision). The mathematical law behind these models is based on an umbrella theory of how the brain

is suggested to function, i.e., the free-energy principle that is outlined in Box 2.

M0)*)&+*')$/!*$9()"-)$/!*"+0)03/#2'*-"8/)-%)6/+/$*'"</)-./)$/02'-0)%4)*E%8/!/+-"%+/7)E$*"+)0-27"/0)

to the ball catching experiments that are presented here. The techniques that were applied to capture

brain activation forced constrained interceptive actions with only few degrees of freedom. Indeed,

participants were sitting or lying during the interception tasks and/or the catching movements did

not require a reaching movement that would disturb postural balance (see study 3). However, since

advance knowledge was shown to have an effect on postural adjustments for catching (study 4) and

*'0%)"+@2/+#/0)E$*"+)42+#-"%+"+6)"+)E*'*+#"+6)-*090)HM79"+)/-)*'5)IJJT[)h*#%E0)/-)*'5)IJJjL()-./)$/'*-"%+)

between advance knowledge and postural adjustments for catching is a promising research avenue PART III

172

PART IIIPART III

for future brain studies. Therefore, optimized techniques will hopefully permit more natural catching

/N3/$"!/+-0)"+)42-2$/)!/-.%7%'%6"/0)0%)-.*-)&$!)#%+#'20"%+0)*$/)3%00"E'/)%+).%1)-./)E$*"+)"0)*#-"8*-/7)

1./+)!*9"+6)*)#*-#.)02##/0042'',)*+7).%1)-."0)"0)"+@2/+#/7)E,)*78*+#/)9+%1'/76/5)

In conclusion, suggestions of relevant brain structures for advance knowledge during interception

*1*"-)-./)-/0-)%4)/!3"$"#*')#%+&$!*-"%+5)U./)4*#-)-.*-)-."0)0-27,)1*0)'"!"-/7)-%)*)E'*#9DE%N)*33$%*#.)

(Keil et al. 2000), can be considered as an important limitation3. Some other limitations of the present

thesis are addressed in the next section, together with the strengths of the current original research.

BOX 2. A UNIFIED THEORY OF THE BRAIN: THE FREE-ENERGY PRINCIPLE

The overview in the main text of this section illustrates a wealth of empirical data in the neurosci-ence of catching. However, a global theory on how the brain works that could unify all those sepa-$*-/)3"/#/0)1*0)'*#9"+6)2+-"')$/#/+-',5)U./)4$//D/+/$6,)3$"+#"3'/)Ha$"0-%+)IJRJL)"0)*+)*--/!3-)-%)&'')this theoretical vacuum. Shortly, this principle suggests that an adaptive system, in casu the brain, will actively resist the natural tendency to disorder, by trying to minimize its free energy. Therefore, the brain (a self-organizing cortical hierarchy) is conceptualized as a statistical machine that constantly makes predictions about the world (based on previous experiences) and updates them based on new sensory information that comes available. Crucially, these predictions are based on prior expec-tations. Accordingly, the advance knowledge effects outlined in the present thesis are suggested to play a vital role in this free-energy principle.

3 Nevertheless, one should be careful not to overestimate the power of brain scanning technology. Brain activity is believed to at most remain just a part of the understanding. The larger picture (behaviour stems from perception and intentions to act upon or not) should not be obscured (Koenderink 1999). See also Michaels and Carello (1981) for a critical note on ‘looking in the brain’ instead of the environment.

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173

5. Strengths and limitations

G,&*"%$&$#5*%0,_&$#K#18.&$*1#,3*"&8,+&.%)%*8*%0,$&0-&*"#&01%3%,8.&1#$#815"&#ZJ#1%)#,*$&

T%*"%,&*"#&J1#$#,*&+05*018.&*"#$%$&81#&"%3".%3"*#+&8,+&(1%#Y7&+%$5'$$#+M&

The present thesis focused on a fundamental research question that might have been overlooked

"+)3$/8"%20)$/0/*$#.)E2-).*0)6$%1+)"+) "!3%$-*+#/)"+)$/#/+-),/*$05)O3/#"&#*'',()-./)%8/$*'')#%+#'20"%+)

%4)-./)3$/0/+-)-./0"0)*770)-%)*)$/0/*$#.)&/'7)1."#.)*7./$/0)-%)*)0"+6'/)3/$#/3-"%+D*#-"%+)*##%2+-)%4)

.2!*+)!%-%$)E/.*8"%2$()E,)0.%1"+6)-.*-)-./)"+@2/+#/)%4)#%6+"-"8/)/44/#-0)02#.)*0)H"!3'"#"-)%$)/N3'"#"-L)

*78*+#/)9+%1'/76/)0.%2'7)+%-)E/)7"0$/6*$7/75)A!3%$-*+-',()*'-.%26.)-."0)"+@2/+#/)1*0)+%-)8"0"E'/)*-)

performance level (equal performance across conditions with or without advance knowledge), the

!/*02$/!/+-)%4)!%8/!/+-)9"+/!*-"#0)$/8/*'/7)/8"7/+#/)4%$)-./)"+@2/+#/)%4)*78*+#/)9+%1'/76/)%+)

visuomotor behaviour. Moreover, the comprehensive measurement of full body kinematics, kinetics and

muscular activity during catching allowed an in depth analysis of postural adjustments for catching, a

topic that hasn’t been investigated thoroughly despite its suggested importance for successful catching

behaviour.

U./$/) *$/) E/+/&-0) *+7) 7$*1E*#90) *00%#"*-/7) 1"-.) -./) 0/'/#-"%+) %4) 6%%7) E*'') #*-#./$0) 1"-.)

experience in ball sports, as was the case in the presented experiments. This homogenous test group

allowed investigation of successful catching behaviour under rather extreme conditions (high ball speeds

*+7)%##'27/7)E*'')-$*:/#-%$"/0L5);%1/8/$()"-)"0)+%-)#'/*$).%1)-./)3$/0/+-)&+7"+6)%+)*78*+#/)9+%1'/76/)

can be extended to less experienced participants and thus be of potential relevance to learning and

instruction. Presumably, a participant must have some experience and thus understanding of what

advance knowledge implies for subsequent visuomotor control.

The small number of participants in study 3 and study 4 needs to be acknowledged. Future research

1"-.)*)'*$6/$)-/0-)6$%23)#%2'7)/+*E'/)-%)&+7)42$-./$)0233%$-)%+)-./)%E0/$8/7)3%0-2$*')*7:20-!/+-0)PART III

174

PART IIIPART III

4%$)#*-#."+65)M'0%()E/#*20/)%4)3$*#-"#*')"!3'"#*-"%+0)H+%-)*'')-%2#./7)-$"*'0).*7)024&#"/+-)!/*02$/!/+-)

quality), mean values across trials were analyzed in all studies except for study 2 that allowed an analysis

at trial level. Nevertheless, future experiments should ascertain how differences between conditions

could be analyzed at trial level so that the variance between trials of the same condition is taken into

account, e.g., by submitting the dependent variables to statistical multilevel modelling techniques.

The presented experiments were deliberately intended to approach real-life settings, with the

catching task allowing many degrees of freedom to be coordinated as compared to more constrained

catching experiments in past research. Notwithstanding this effort towards a representative design,

6/+/$*'"<"+6)-./)3$/0/+-)&+7"+60)-%)03%$-0)&/'70)0.%2'7)E/)-*9/+)1"-.)#*2-"%+5)O"+#/)*)E*''D3$%:/#-"%+)

machine does not provide information of the opponent, its use is likely to generate different movement

outcomes (see Shim et al. 2005; Pinder et al. 2009). Nevertheless, the observed differences caused by

advance knowledge provide a good starting point to discuss the practical relevance and propose some

future research directions, as will be outlined in the next section.

:9;9^@C&4GIABIIGE;

175

6. Practical relevance and future directions

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#ZJ#1%)#,*8.&)#*"0+0.03%#$M& G,& 3#,#18._& *"#& J0$$%(.#& %,Y'#,5#& 0-& 8+K8,5#& S,0T.#+3#&

$"0'.+&(#&85S,0T.#+3#+&%,&#ZJ#1%)#,*8.&+#$%3,$&+#J#,+%,3&0,&*"#&1#$#815"&2'#$*%0,$M&

?%,8..7_&$0)#&50,$#2'#,5#$&-01&"')8,&(#"8K%0'1&8,+&3'%+#.%,#$&-01&$J01*$&J185*%*%0,#1$&

81#&$'33#$*#+M&

6.1. Future experimental designs: a plea for situation-dependent research

gMMM_&8'*"01$&*#,+&*0&30&+%1#5*.7&-10)&*"#&+8*8&*0&*"#&*"#017M&!"#7&81#&%,5.%,#+&*0&0)%*&*"#&

%,*#1)#+%8*#&$*83#&0-&+#5%+%,3&*"#&#Z*#,*&*0&T"%5"&*"#&#ZJ#1%)#,*8.&1#$'.*$&81#&+#*#1)%,#+&

(7&*"#&+#$%3,&0-&*"#&#ZJ#1%)#,*Mh&

U*9%1*0)dELJGeF)$=)CL=

The results of the presented experiments have a clear methodological implication for future

$/0/*$#.)%+)"+-/$#/3-"8/)E/.*8"%2$5)O3/#"&#*'',()1./+)0-27,"+6)!%-%$)E/.*8"%2$()%+/)#*++%-)7"0$/6*$7)-./)

"+@2/+#/)%4)*78*+#/)9+%1'/76/)%+)!%8/!/+-)/N/#2-"%+5)U./$/4%$/()1/)/+#%2$*6/)42-2$/)/N3/$"!/+-*')

methodologies to at least consider such expectations and, if possible, to control for it in a carefully

7/0"6+/7)/N3/$"!/+-*')0/-D235)M0)#%+0"7/$/7)E/'%1()-."0)+%)7%2E-)7/3/+70)%+)-./)03/#"&#)$/0/*$#.)

questions that are to be solved.

When it is attempted to study isolated, instantaneous information sources (e.g., visual information

cues illustrated in section 3 of Part 1) and/or control parameters that guide interceptive behaviour in

PART III

176

PART IIIPART III

order to gain further insight in the fundamental and theoretical underpinnings of visuomotor control, it

0//!0)$/'/8*+-)-%)-$,)-%)!"+"!"</)-./)"+@2/+#/)%4)#*'"E$*-"%+)3$%#/00/0)E*0/7)%+)*78*+#/)9+%1'/76/)

of repeated trials. For these experiments, randomized task conditions (e.g., speed or position) seem

worthwhile to pursue4.

When one wishes to conduct experiments that are to be relevant for real life situations, the

%E:/#-"8/)"0)-%)0//9)6/+/$*'"<*-"%+)%4)$/0/*$#.)&+7"+60)%2-0"7/)%4)03/#"&#)/N3/$"!/+-*')#%+-/N-0)H"5/5()

representative design; Davids et al. 2006). Consequently, the implementation of button press, motion-

prediction and judging tasks for studying visuomotor behaviour has been criticized in the past decades

for undervaluing the tight link between perception and action (Bootsma 1989; Tresilian 1995; Davids

et al. 2001b; Dicks et al. 2010). To overcome such concerns, natural interceptive actions have been

studied that preserve perception-action coupling (see the overview of ball catching experiments in

0/#-"%+)I)*+7)_)%4)Q*$-)RL5) A!3%$-*+-',().%1/8/$() -./)3$/0/+-) $/0/*$#.)&+7"+60) 0266/0-) -.*-) -./) 0%D

called 0219,2% interceptive actions might undervalue the mediating cognitive (i.e., advance knowledge)

context that will be available in sports situations and daily life. Since research in sports psychology has

typically focussed on substantiating expertise effects, it appears peculiar that it may have excluded

by using random designs, those unique context properties (i.e., advance knowledge) that guide an

expert to successful performance (Araujo et al. 2007). Consequently, to opt for a random-order or

blocked-order design and/or to give explicit advance cues will be a complex and sometimes paradoxical

decision that requires a proper consideration of the real-life situation one intends to generalize to (e.g.,

competition or public road environment). Clearly, such an account will create more degrees of freedom

and increase complexity in experimental designs. Although the many multifarious aspects of real-life

situations are always supposed to be more complex than any experimental condition and consequently,

certain reductions seem insurmountable (Nitsch 2009), the present thesis demonstrated that advance

knowledge should at least be acknowledged in designing such experiments. Integration of the newest

techniques in motion capture, video simulation and, for catching experiments, precise ball launching

devices (d’Avella et al. 2011), might pave the way for a more complete integrated account in laboratory

settings. Examples already exist for hitting in baseball and cricket (see, e.g., ProBatter Sports, LLC,

]"'4%$7()cU()^OML)-.*-)*''%1)-%)"+#'27/)8*$,"+6)03%$-)03/#"&#)-*#-"#*')0"-2*-"%+0)"+)-./)*#-%$D/+8"$%+!/+-)

4 A review of previous real ball catching experiments shows that only one third had a random design. Most experiments were conducted in blocks of the same ball speed, position, perturbation, etc.

:9;9^@C&4GIABIIGE;

177

system. Additionally, virtual reality environments might be another tool to create representative designs,

3$%8"7/7)-.*-)-./)/N3/$"!/+-*')/+8"$%+!/+-)"0)024&#"/+-',)-$*+04/$*E'/)-%)-./)"+-/+7/7)/+8"$%+!/+-)

H"5/5()*#-"%+)&7/'"-,[)O-%44$/6/+)/-)*'5)IJJ_[)M$*2:%)/-)*'5)IJJZL5)a%$)*+)/N*!3'/()-./)$/*7/$) "0)7"$/#-/7)

toward a series of experiments on baseball hitting, which illustrated how an experimental design can

incorporate advance knowledge (the history of previous pitch speeds) in the study of visuomotor

behaviour (Gray 2002a,b).

In conclusion, next to requiring a meaningful coupling between perception and action, representative

7/0"6+0) 0.%2'7) $/#9%+)1"-.) -./) "+@2/+#/)%4) *78*+#/)9+%1'/76/)%+)8"02%!%-%$)E/.*8"%2$5)M0) 02#.()

opportunities are created for actions that represent more closely the functional behaviours of the

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exciting challenges await future research in human visuomotor behaviour.

6.2. Daily life and sports context

go& *"#& 1#$'.*%,3& (#"8K%0'1& 0-& *"#& 308.S##J#1& T%..& +#J#,+_& ,0*& 0,.7& 0,& K81%0'$&

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8.$0&0,&J8$*&#ZJ#1%#,5#&8,+&)#)01%#$_&8$&T#..&8$&*"#&$*1#,3*"&0-&%,*#,*%0,8.&%,-01)8*%0,&*"8*&

"#&01&$"#&(1%,3$&*0&*"#&$%*'8*%0,Mh&

`2+"(3)'1)2%=)dCDDE2eF)$=)EGJ=

Daily-life activities such as walking through a door, grasping a cup of coffee or driving a car perhaps

permit a cognitively undemanding perception-action coupling. Nevertheless, advance knowledge of

*)0277/+)3/$-2$E*-"%+)02#.)*0)*) 0'"33/$,)@%%$) Hc.*!)*+7)Y/74/$+)IJJI[)]*$"6%'7)*+7)Q*-'*)IJJI[)

Heiden et al. 2006) or a unbalancing push (Santos et al. 2010) will alter the postural response in order

-%)!*"+-*"+) />2"'"E$"2!5)M'0%() $/*#-"%+) -"!/) 4%$) .2!*+) E$*9/) E/.*8"%2$) "+) -$*4&#) 0"-2*-"%+) 7/3/+70)

heavily on the expectation (and thus advance knowledge) of the necessity to brake (Green 2000).PART III

178

PART IIIPART III

Sports might be different from these daily life activities because of its complex, time-pressured

/+8"$%+!/+-)*+7)-./)."6.',)03/#"&#)*+7)%4-/+)*$-"&#"*')-*09)#%+0-$*"+-0)HO2!!/$0)RSSI[)P//9)IJJSL5)

Therefore, many sports contexts will stimulate movement outcomes that are more ‘representation

hungry’ (Clark 1997). For example, hidden aspects of the environment (e.g., sudden occlusions of the

puck in ice hockey) will encourage predictive behaviour (Warren 2006); and decision making on the

&/'7)H/565()3*00"+6()7$"EE'"+6)%$)0.%%-"+6)"+)E*'')03%$-0L)1"'')'/*7)-%)0-$*-/6"#)E/.*8"%2$)Hf*$$/+)IJJT[)

Raab et al. 2009; Beek 2009) that goes beyond the exclusive use of instantaneous sensory information.

Note however that in the present experiments, experienced ball catchers managed to perform equally

with or without advance knowledge, although the movement outcome was different. It remains to be

"+8/0-"6*-/7)"+)42-2$/)$/0/*$#.)1.*-)1%2'7)E/)-./)"+@2/+#/)%4)*78*+#/)9+%1'/76/)4%$)+%8"#/)%$)'/00D

experienced sportsmen, since these groups are suggested to rely more heavily on internal aspects of

09"'')/N/#2-"%+)H"+)#%+0-$*0-)-%)/+8"$%+!/+-*')E*'')@"6.-)"+4%$!*-"%+[)c*0-*+/7*)*+7)=$*,)IJJZL)*+7)%+)

cognitive aspects of the movement task (Magill 2004; Nitsch 2009).

In practical terms, the question remains how sports coaches could incorporate this understanding

in appropriate training programs. Recently, it has been underscored that representative learning designs

0.%2'7)/+02$/) 42+#-"%+*'"-,)*+7)*#-"%+)&7/'"-,) "+) "+-/$8/+-"%+0) 02#.)*0)#%*#."+6()!%-%$) '/*$+"+6)*+7)

training (Pinder et al. 2011a, p.151): “Practitioners should design dynamic interventions that consider

interacting constraints on movement behaviours, adequately sample informational variables from the

03/#"&#)3/$4%$!*+#/)/+8"$%+!/+-0()*+7)/+02$/)-./)42+#-"%+*')#%23'"+6)E/-1//+)3/$#/3-"%+)*+7)*#-"%+)

processes”. The current studies additionally emphasize that amongst these informational variables,

cognitive factors such as advance knowledge should not be neglected (see also part 1, section 2, Fig. 2).

For example, the use of ball projection machines (e.g., in tennis, baseball and cricket) for blocked-order

practice of isolated movement aspects might need a critical evaluation (see, e.g., Pinder et al. 2011b)

given that task constraints such as human factors (e.g., variability in ball speed was observed when

balls are propelled by humans; Moras et al. 2008; Werner et al. 2008) and aerodynamic effects of ball

trajectories (Mehta and Pallis 2001) are suggested to induce randomness in interceptive behaviour.

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ACKNOWLEDGMENTS

Many thanks to Kees Brunia, Andreja Bubic, Keith Davids, Rita De Oliveira, Joost Dessing, Karl Friston,

Claire Michaels, Eric Laurent, Joan López-Moliner, Karl Newell, Joel Norman, Giovanni Pezzulo, Nigel

Stepp, James Tresilian, Daniel Wolpert and Yuji Yamamoto for useful interpretations of the presented

$/0/*$#.)&+7"+60)*+7)8*'2*E'/)#%!!/+-0)"+)#%+0-"-2-"%+)%4)-."0)6/+/$*')7"0#200"%+5))

PART III

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PART IIIPART III

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191

IBFF@ D̂

I@F9;i@!!G;:

IBFF@ D̂

The skill of catching has drawn attention to motor control researchers because reaching out

*+7)6$*03"+6) *)E*'') .*0) 8/$,)&+/) 03*-"%-/!3%$*') $/>2"$/!/+-05)U./0/) *#-"%+0)3$/#"0/',) "''20-$*-/) -./)

human visuomotor system’s capacities of closely coupling visual information of the environment (an

*33$%*#."+6)E*''L)-%)%+/G0)%1+)!%8/!/+-)H$/*#."+6)-./).*+7)-%1*$70)-./)E*'')*+7)#'%0"+6)-./)&+6/$0)

at time). However, the role of advance knowledge as a non-instantaneously available information source

-.*-)!"6.-)"+@2/+#/)*$!)*+7).*+7)9"+/!*-"#0().*0)E//+)%4-/+)%8/$'%%9/7)1./+)0-27,"+6)-./)#%+-$%')

of such visually guided interceptive actions. Therefore, the present thesis covers some original research

experiments investigating the effect of advance knowledge. Additionally, it was questioned how advance

knowledge could have an effect on the postural adjustments that accompany a catching action.

Research

Four studies were conducted with good ball catchers. From a standing position, they were required

to catch tennis balls while task conditions were either varied from trial-to-trial or repeated several times.

Movement execution was registered to enable a three-dimensional analysis of arm and hand kinematics.

A+)-./)&$0-)0-27,()"-)1*0)0.%1+)-.*-)"!3'"#"-)*78*+#/)9+%1'/76/)%4)E*'')03//7()6*-./$/7)-.$%26.)-./)

repetition of trials in blocks of the same ball speed, had an effect on hand movements. With advance

knowledge, the initial hand movement was more scaled to ball speed than when catching in a random

situation with unknown ball speed. Although expectancy of the upcoming ball speed is proposed to

yield these functional differences, an alternative explanation suggests that the observed differences can

be explained as a consequence of trial-by-trial history in which the movement is prepared based on the

preceding trials without much cognitive involvement.

SUMMARY

194

In a second study, this trial-by-trial history effect was minimized during a catching task during which a

visual occlusion could emerge. In one condition, explicit advance knowledge of occlusion (no, early or late)

was provided before each trial, in the other condition no such information was given. Again, differences

in arm and hand kinematics were observed that can be attributed to expectations of occlusion. Such

explicit advance knowledge resulted in an adapted wrist transport and increased grasping time, while a

higher maximal wrist velocity allowed to overcome the uncertainty of unexpected occlusions.

M)+/N-)0-/3)1*0)-%)-/0-)1./-./$)*78*+#/)9+%1'/76/)1%2'7)*'0%)"+@2/+#/)-./)3%0-2$*')*7:20-!/+-0)

for catching and how this was integrated with the movement kinematics. Because detailed information

on the particular mechanism of postural control during catching was lacking, postural adjustments when

$*"0"+6)-./)*$!)4%$)#*-#."+6)1/$/)&$0-)#%!3*$/7)-%)*)1/''D7%#2!/+-/7)*$!)$*"0"+6)-*09)"+)$/*#-"%+)-%)

the appearance of the ball. It was shown that different postural adjustments are imminent between the

two tasks: an ankle strategy in accordance with an inverted pendulum mechanism for catching and an

additional counter-rotating mechanism at hip level for reaction-time arm raising.

A+)*)&+*')0-27,()-./)&+7"+60)%4)!%$/)0#*'/7)*$!)9"+/!*-"#0)1./+)*78*+#/)9+%1'/76/)%4)E*'')03//7)"0)

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postural response when catching at high ball speed.

Conclusions

U./)$/3%$-/7)$/0/*$#.)&+7"+60)#%+&$!)-./)"+@2/+#/)%4)*78*+#/)9+%1'/76/)%+)!%8/!/+-)E/.*8"%2$)

during interceptive actions. Although advance knowledge did not increase catching performance in skilled

participants, the associated adaptations, depending on the advance knowledge context, underscore

its importance. Theoretically, these advance knowledge effects imply some cognitive representation

which is hard to reconcile with a strict ecological perspective that minimizes any cognitive mediation.

Conversely, a computational approach conceptualizes advance knowledge as an optimizing prior in the

constitution of a complete representation of task and environment. The observed effects of advance IBFF@ D̂

195

knowledge might not permit a judgement call on both perspectives, nevertheless they emphasize a

certain cognitive involvement, whether it be full-blown or not, guiding visuomotor behaviour.

a$%!)*)3$*#-"#*')3%"+-)%4)8"/1()-./)#2$$/+-)&+7"+60)1*$+)$/0/*$#./$0)-%)*#9+%1'/76/)-./)"+@2/+#/)

of advance knowledge in the design of experiments and advice practitioners to account for these

effects in sports and daily-life environments.

SUMMARY

196

I@F9;i@!!G;:

Het vangen van een bal vraagt een nauwe koppeling tussen visuele informatie uit de omgeving (het

zien van een naderende bal) en je eigen bewegingen (het reiken van de hand naar de bal toe en het

precies op tijd sluiten van de vingers). Deze vaardigheid trok dan ook de aandacht van onderzoekers in

./-)7%!/"+)8*+)7/)!%-%$"0#./)#%+-$%'/)%!1"''/)8*+)7/)03/#"&/9/)$2"!-/'":9/)/+)-/!3%$/'/)-**98/$/"0-/+)

die het stelt aan het visueel-motorische systeem. Wat echter vaak over het hoofd werd gezien, is dat

er ook informatie van tel kan zijn die niet op het ogenblik zelf opduikt, maar reeds ervoor aanwezig is.

Zo kan voorkennis een zekere invloed hebben op de arm- en handbewegingen van visueel gestuurde

interceptieve vaardigheden. In deze doctoraatsthesis werden dan ook enkele experimenten uitgevoerd

om dit mogelijke effect van voorkennis dieper te onderzoeken. Daarbij werd ook de vraag gesteld of en

hoe deze voorkennis een invloed kan hebben op de evenwichtsaanpassingen die met vangbewegingen

gepaard gaan.

Onderzoek

Er werden vier studies uitgevoerd waaraan telkens goede balvangers deelnamen. De taak bestond

eruit tennisballen te vangen vanuit stilstand waarbij bepaalde taakeigenschappen werden gemanipuleerd

en dit van de ene poging op de andere of over herhaalde metingen. Hogesnelheidscamera’s maakten

het mogelijk een driedimensionale weergave van de vangbeweging te reconstrueren.

In een eerste studie werden ballen aangeboden met een verschillende balsnelheid, met of zonder

voorkennis van die balsnelheid. Impliciete voorkennis van balsnelheid werd veroorzaakt door de

herhaling van pogingen in blokken van steeds dezelfde snelheid. Dit zorgde ervoor dat de handbeweging

aanvankelijk meer was afgestemd op deze balsnelheid in tegenstelling tot het vangen in een willekeurige

situatie (random) aan een ongekende balsnelheid. Dit betekent dat de verwachting die gecreëerd wordt IBFF@ D̂

197

door het aanbieden van ballen aan eenzelfde snelheid, zorgt voor verschillen in bewegingsuitvoering.

Een alternatieve verklaring voor de geobserveerde verschillen oppert echter dat de loutere herhaling

van poging per poging aan dezelfde balsnelheid ervoor zorgt dat de beweging wordt klaargestoomd

enkel gebaseerd op de voorgaande pogingen en dus zonder dat er veel cognitie aan te pas dient te

komen.

Daarom werd in een tweede studie dit effect van herhaalde pogingen tot een minimum herleid aan

de hand van een experiment waarbij het zicht kon verdwijnen tijdens het vangen. In de ene conditie werd

er voor elke poging expliciete voorkennis verschaft over het al dan niet verdwijnen van het zicht (niet,

vroeg of laat), in de andere conditie werd deze informatie niet gegeven. Opnieuw werden verschillen

in de arm- en grijpbewegingen vastgesteld die kunnen worden toegeschreven aan de verwachtingen

die de proefpersonen hadden over het verdwijnen van het zicht. Deze expliciete voorkennis resulteert

namelijk in een aangepaste polsbeweging en een verlengde grijptijd, terwijl een hogere maximale

polssnelheid de vangers toelaat de onzekere situatie van onverwachte gezichtsverstoringen te omzeilen.

Een volgende stap bestond eruit te testen of voorkennis ook een invloed zou hebben op

evenwichtsaanpassingen tijdens een vangbeweging en hoe deze dan met de eigenlijke vangbeweging

92++/+)6/u+-/6$//$7)1%$7/+5)C!7*-)./-) 03/#"&/9/)/8/+1"#.-0!/#.*+"0!/)E":)./-) 8*+6/+)8*+)//+)

bal nog zo goed als onbekend was, werden de evenwichtsaanpassingen bij het vangen van een bal aan

hoge snelheid eerst vergeleken met een reeds goed gedocumenteerde taak die eruit bestond de arm

enkel zo snel mogelijk te heffen bij het zien van de bal (een reactietijdtaak). Voor vangen werd een

strategie vastgesteld die zich vooral rond de enkel afspeelde, namelijk volgens het evenwichtsprincipe

van een omgekeerde slinger. Bij het heffen van de arm in de reactietijdtaak was er ook een bijkomend

mechanisme te merken waarbij de lichaamssegmenten in tegengestelde richtingen rond de heup draaien.

Een laatste studie bevestigde de bevindingen van een beter afgestemde armbeweging door

voorkennis van balsnelheid. Bovendien werd er aangetoond dat voorkennis ook toelaat om een minder

uitgesproken evenwichtsaanpassing uit te voeren wanneer men aan de hoogste balsnelheid vangt.

SUMMARY

198

Conclusies

De huidige onderzoeksresultaten bevestigen de invloed van voorkennis op het bewegingsgedrag bij

interceptieve vaardigheden. Hoewel deze voorkennis bekwame proefpersonen niet beter doet vangen,

kan het belang van deze bevindingen toch niet onderschat worden aangezien er bewegingsaanpassingen

werden vastgesteld die afhangen van de al dan niet gecreëerde voorkennis. Dit lijkt op het eerste zicht

logisch, maar het impliceert wel een vorm van cognitieve representatie van de werkelijkheid die moeilijk

te rijmen valt met een strikt ecologische benadering op motorisch gedrag waarin men een directe

perceptie-actie koppeling, zonder inmenging van cognitieve processen, voorstelt. Een computationele

benadering ziet voorkennis dan weer als handige informatie bij de optimalisering van het model van

de werkelijkheid dat wordt gevormd voorafgaand aan de eigenlijke beweging. Hoewel de aangetoonde

effecten van voorkennis niet toelaten uitsluitsel te geven over elk van beide invalshoeken, benadrukken

ze wel een bepaalde, al dan niet geheel ontwikkelde, vorm van cognitieve betrokkenheid die de beweging

kan aansturen, los van momentane visuele informatie.

Vanuit praktisch standpunt waarschuwen de huidige onderzoeksresultaten onderzoekers ervoor

om de invloed van voorkennis te erkennen bij het opzetten van experimentele designs en adviseren

ze bewegingsdeskundigen in het werkveld om rekening te houden met deze effecten bij sporten en

dagdagelijkse activiteiten.

IBFF@ D̂

199

96GCE:B9

Back to your son’s soccer tournament. The opponent rushes towards the

ball. Indeed, a die-hard ball in the right corner. Luckily, your son goes quickly

for that right corner. It is very likely that he took advantage of the advance

knowledge that a high ball speed was going to arrive in the right corner. Sure,

perhaps he could have make it also without this advance knowledge, by moving

differently. But the advance knowledge gave him a head start for success.

Time now for a well-deserved victory celebration.

CGI!&E?&6BcCGA@!GE;I

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Tijtgat P, Vanrenterghem J, Bennett SJ, De Clercq D, Savelsbergh GJP, Lenoir M. (In revision) Postural

adjustments in catching: on the interplay between segment stabilization and equilibrium control. Q*1*,)

A*01,*%

Tijtgat P, Vanrenterghem J, Bennett SJ, De Clercq D, Savelsbergh GJP, Lenoir M. (2012) Implicit

advance knowledge effects on the interplay between arm movements and postural adjustments for

catching. Y'9,*36"'06')V'11',3F)GEP, 117-121

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of explicit advance knowledge of occlusion on interceptive actions. ?/$',"#'012%)R,2"0)K'3'2,65F)CEI,

483-490

Tijtgat P, Bennett SJ, Savelsbergh GJP, De Clercq D, Lenoir M (2010) Advance knowledge effects on

kinematics of one-handed catching. ?/$',"#'012%)R,2"0)K'3'2,65F)CDE, 875-884

Tijtgat P, Mazyn L, De Laey C, Lenoir M (2008) The contribution of stereo vision to the control of

braking. ^66"('01)̂ 02%:3"3)20()U,'+'01"*0F)ID, 719-724

6117&,8)9*"$-

Tijtgat P, Bennett SJ, Savelsbergh GJP, De Clercq D, Lenoir M (2011). To know or not to know:

adaptations to expected and unexpected visual occlusions in interceptive actions. In !19("'3)"0)U',6'$1"*0)

20()261"*0)p\= (edited by Charles E, Smart LJ). New York, USA: Taylor & Francis. pp 99-104

Tijtgat P, Mazyn L, Lenoir M (2007) Kijk eens diep met je ogen. In R'-'8"083-'1'03652$)"0)<'-'8"08W)

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M, Phillipaerts R), Gent, Belgium: Vakgroep Bewegings- en Sportwetenschappen. pp 53-55

204

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Tijtgat P, Bennett SJ, Savelsbergh GJP, De Clercq D, Lenoir M (2010) Advance knowledge effects on

kinematics of one-handed catching. !$*,1)'0)H'0''3490('=)IM, 32-33

Tijtgat P, De Clercq D, Bennett SJ, Savelsbergh GJP, Lenoir M (2008) Differences in performance and

kinematics when catching under block versus random temporal constraints. \01',021"*02%)O*9,02%)*.)!$*,1)

U3:65*%*8:F)IE, SI4 110-111.

Lenoir M, Tijtgat P, De Clercq D, Bennett SJ, Savelsbergh GJP (2008) Spatial and temporal accuracy

do not emerge simultaneously during the learning of a one-handed catch. O*9,02%)*.)!$*,1)Z)?/',6"3')

U3:65*%*8:F)MD, S105-S106.

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of advance knowledge of ball speed on postural adjustments in one-handed catching Poster presentation

at the CD15)B*,%()A*08,'33)*.) 15') \01',021"*02%)!*6"'1:) .*,)U*319,')20()H2"1)K'3'2,65) d\!UHKe) k)H2"1)Z)

Q'012%)]9061"*0, Trondheim, Norway

Tijtgat P, Vanrenterghem J, Bennett SJ, De Clercq D, Savelsbergh GJP, Lenoir M. (2012). Are postural

adjustments in catching equilibrium control or movement support? Poster presentation at the CD15)

B*,%()A*08,'33)*.)15')\01',021"*02%)!*6"'1:).*,)U*319,')20()H2"1)K'3'2,65)d\!UHKe)k)H2"1)Z)Q'012%)]9061"*0,

Trondheim, Norway

Tijtgat P, Bennett SJ, Savelsbergh GJP, De Clercq D, Lenoir M (2011). To know or not to know:

adaptations to expected and unexpected visual occlusions in interceptive actions. Poster presentation

at the E15)\01',021"*02%)A*0.','06')*0)U',6'$1"*0)20()̂ 61"*0)d\AU^eF Ouro Preto, Brazil

205

Tijtgat P, Savelsbergh GJP, De Clercq D, Bennett SJ, Lenoir M. (2009). Lateral is not three-dimensional

interception: a test of the required velocity model in unconstrained real catching. Poster presentation at

U,*8,'33)"0)Q*1*,)6*01,*%)T\\)dUQAeF Marseille, France

Tijtgat P, De Clercq D, Bennett SJ, Savelsbergh GJP, Lenoir M (2008) Differences in performance and

kinematics when catching under block versus random temporal constraints. Oral presentation at)15')

C0()\01',021"*02%)A*08,'33)*.)A*#$%'/)!:31'#3)"0)!$*,1)d\AA!!e)k)ED15)?9,*$'20)B*,435*$)*.)?6*%*8"62%)

U3:65*%*8:)d?B?Ue, Madeira, Portugal

Lenoir M, Tijtgat P, De Clercq D, Bennett SJ, Savelsbergh GJP (2008) Spatial and temporal accuracy

do not emerge simultaneously during the learning of a one-handed catch. Poster presentation at the

A*0.','06')*.)Y*,15)̂ #',"620)!*6"'1:).*,)15')U3:65*%*8:)*.)!$*,1)20()U5:3"62%)̂ 61"+"1:)dY^!U!U^e, Niagara

Falls, Canada

Tijtgat P, Mazyn LIN, Lenoir M (2007) The contribution of visual information to human brake

behaviour. Poster presentation at the EC15)R";20092%)*.)15')̂ 33*6"21"*0)('3)A5',65'9,3)'0)̂ 61"+"1q3)U5:3"b9'3)

'1)!$*,1"+'3)d^A^U!eF Leuven, Belgium

Tijtgat P, Mazyn LIN, Lenoir M (2007) The contribution of visual information to human brake

behaviour. Oral presentation at the ?9,*$'20)B*,435*$)*0)Q*+'#'01)!6"'06')d?B>Q!e, Amsterdam,

The Netherlands

U":-6*-)Q()U*''"$) A()]20#.)g()i*'#9/)]()Y**E)]()B/+%"$)])HIJJZL)U./) "+@2/+#/)%4)0-$/00)*+7)!20#'/)

fatigue on implicitly and explicitly learned motor skills. Oral presentation at the ?9,*$'20)B*,435*$)*0)

Q*+'#'01)!6"'06')d?B>Q!e, Amsterdam, The Netherlands

206

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Tijtgat P, Vanrenterghem J, Bennett SJ, De Clercq D, Savelsbergh GJP, Lenoir M. (2012). Are postural

adjustments in catching equilibrium control or movement support? Poster presentation at the ES15)

!:#$*3"9#)*.)15')]%'#"35)!*6"'1:).*,)_"0'3"*%*8:)dT_e, Ghent, Belgium

Tijtgat P, Bennett SJ, Savelsbergh GJP, De Clercq D, Lenoir M (2010). Adaptations to expected and

unexpected visual occlusions in interceptive actions. Poster presentation at the EG15)!:#$*3"9#)*.)15')

]%'#"35)!*6"'1:).*,)_"0'3"*%*8:)dT_e, Antwerp, Belgium

Tijtgat P, Bennett SJ, Savelsbergh GJP, De Clercq D, Lenoir M (2009) Advance knowledge effects on

kinematics of one-handed catching. Oral presentation at the EI15)!:#$*3"9#)*.)15')]%'#"35)!*6"'1:).*,)

_"0'3"*%*8:)dT_e, Leuven, Belgium

Tijtgat P, Mazyn LIN, Lenoir M (2007) The contribution of visual information to human brake

behaviour. Poster presentation at the EC15)!:#$*3"9#)*.)15')]%'#"35)!*6"'1:).*,)_"0'3"*%*8:)dT_e, Ghent,

Belgium

Tijtgat P (2006). Implicit and explicit learning in darts. Oral and poster presentation at the EE15)

!:#$*3"9#)*.)15')]%'#"35)!*6"'1:).*,)_"0'3"*%*8:)dT_eF Antwerp, Belgium

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