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Does the modality in which information

is presented influence how it is remembered?

Human information tends to be organised

predominantly in either verbal or spatialPsicothema, 1999. Vol. 11, nº 4, pp. 747-767 ISSN 0214 - 9915 C!"N PS#"$Cop%&i'ht ( 1999 Psicothema

Psicothema, 1999 747

MEMORY IN TOUCH

Susanna Millar Oxford niversity

Models of short!term memory have to ta"e into account that touch is not a tightly organised single

modality# $ouch% without vision or other external cues% depends on information from touch% movementand from body!centred &posture' cues# $hese inputs vary with the si(e and types of ob)ect% and with

tas" demands# *t is argued that the convergence and overlap of inputs from different sources is crucial

to parsimonious organisation for memory and recall# +Modality!specific, input conditions thus form anintegral part of the available information% which changes% and is changed by longer!term information#

$hree general principles apply- &i' .arsimony of coding modality!specific inputs for recognition and recall/

&ii' lin"s with output systems which can +rehearse, information/ and &iii' longer!term familiaritywith procedures and types of coding# $he introduction and first section discuss these points in relation

to models for hearing and vision# $he third section cites findings on modality!specific tactual memory%and explains tactual memory spans in terms of paucity versus redundancy of reference information to

organise inputs spatially# Movements are considered next as inputs and as spatially organised outputs

that can provide haptic rehearsal# $he final section argues that intersensory modality!specific processesand longer!term memory need to be included as interrelated systems in S$M models in order to account

for memory in touch#

La memoria en el tacto. 0os modelos de memoria a corto pla(o deben tener en cuenta 1ue el tactono es una modalidad 2nica estrechamente organi(ada# 3l tacto sin visin u otras claves externas% depende

de la informacin obtenida a partir del tacto% del movimiento y de las claves &la postura' centradas

en el cuerpo# 3stos inputs var5an con el tama6o y los tipos de ob)etos% y con las demandas de la tarea#0a convergencia y el solapamiento de los inputs a partir de diferentes fuentes es crucial para la organi(acin

de la memoria y el recuerdo# 0as condiciones del input +espec5ficas de la modalidad forman

una parte integral de la informacin disponible% 1ue cambia% y es cambiada por la informacin a largo pla(o# $res principios generales pueden aplicarse- &i' 0a parsimonia de la codificacin de los inputs espec5ficos

de la modalidad para el reconocimiento y el recuerdo/ &ii' las uniones con los sistemas del output 1ue pueden +repetir, la informacin/ y &iii' mayor familiaridad con los procedimientos y los tipos

de codificacin# 3n la introduccin y en la primera seccin se discuten estos puntos en relacin con losmodelos de visin y audicin# 0a tercera seccin cita resultados sobre la memoria del tacto espec5ficade la modalidad% y explica la amplitud de la memoria tctil en funcin de la pobre(a versus la redundancia

de informacin de referencia para organi(ar los inputs de manera espacial# Despu8s se consideran

los movimientos como inputs y outputs organi(ados espacialmente 1ue pueden proporcionar repeticinhptica# 3n la seccin final se argumenta 1ue los procesos intersensoriales espec5ficos de la modalidad

y la memoria a largo pla(o necesitan ser incluidos como sistemas interrelacionados en los modelos

de M9. para poder explicar la memoria en el tacto#Correspondencia: Susanna Millar Department of Experimental PsichologyOxford UniversitySouth Parks oad O!" #UDOxford $United %ingdom&

Does the modality in which information

is presented influence how it is remembered?

Human information tends to be organised predominantly in either verbal or spatial

form# *nterestingly% each is connected with a

particular sense modality- Space with vision%language with hearing# $ouch does not

have such a well!defined lin" with a particular

form of "nowledge# :eeling texture%

temperature% pressure and pain in whichtouch is specialised% belong more to the

+1ualia, of experience ;as do colour in vision%



or pitch in hearing;% than to specifically

linguistic or spatial forms of organising

information# $he lin"s between vision

and space% hearing and language are not% of course% exclusive# <isual icons% scripts%

signs and gestures can carry verbal information#

Distance% direction% and even shape

can be remembered from hearing sound patternsand verbal descriptions# $ouch can

convey both forms of information#

*s there% therefore% any need to include

the perceptual modality of inputs in modelsof memory? * shall argue that there is# $he

+medium, is not the +message,# =ut the

perceptual conditions in which inputs occur%

and the lin"s between perception and outputsystems% are an integral part of the type and

amount of information that is available% and

how that information is processed and remembered#

$he general framewor" * prefer for describing

information processing and memoryuses the metaphor of dynamic networ"s of

interrelated and converging processes &Millar%>4% >7'# *t focuses on active processing

of the information that is available

to the organism from external and internal

sources# $he contrast is with metaphors thatimply a static architecture# Such metaphors

underplay the continual% reciprocal influence

of previous and current information in

processing% though that is obvious even inorder effects in experimental presentations#

@rchitectural metaphors suggest a rigid hierarchical

&+bottom!up, or +top!down,' organisation#Separate inputs from the modalitiesare either integrated at the top level by

a separate translation mechanism% or simply

subserve a top!level abstract description

that obtains for all inputs# Metaphors thatimply active networ"s of interacting and

converging processes accord better with current

findings on neural connections in the

constantly active brain# $hus inputs frommultisensory sources seem to converge in

varying combinations in a number of brain

areas# @bove all% the metaphor of active%

converging processes is needed for touch#$ouch is not a single modality% nor even

a single perceptual system# Ahat we call

+touch, refers to combinations of a number

of different% converging sources of informationthat include inputs from some s"in receptors

to greater or lesser extents# $he notion

of perceptual systems that receive inputs

from several sources is true also for other perceptual systems &Bibson% >CC'#



=ut in touch% the combinations of inputs

vary with the type% si(e% meaning and familiarity

of ob)ects% as well as with current information%

and importantly also% with tas" demands# $he 1uestions we as" about memory

in touch thus have to be seen in the

context of the combinations of disparate inputs

that need to converge for recognitionand short!term recall in different haptic conditions#

=ecause differences in informational

conditions are particularly important in

touch% the present paper focuses on shorttermmemory for raised line configurations%

rather than on ob)ect recognition# $he neural

pathways in identifying ob)ects &what?'

and locations &where?' are not precisely thesame &e#g# @nderson% >7/ Schneider%

>C7/ Aeis"rant(% >C'# Eecognising familiar

manipulable ob)ects% that have well"nown

names% taps into a wide range of semantic

"nowledge and meaningful verbaldescriptions of their every day use and even

their visual appearance for sub)ects who havethe experience# .rior "nowledge has to

be considered in examining short!term memory#

=ut it is more circumscribed% and so!MEMO' () *OUC+

74 Psicothema, 1999

mewhat differently focused% in short!term

memory tas"s that demand recognition or

recall of relatively unfamiliar tactual raised

line and dot patterns# $he present paper centreson the information that is available to

sub)ects in such haptic conditions#

$he paper is divided into several sections#

$he first section briefly describes somerelevant theoretical models of shortterm

memory# Since they are predominantly

based on findings with visual and verbal

materials% these are considered first to establishthe context in which findings on memory

for touch must be examined# $he next

two sections survey findings from studies

on memory for what is generally called+touch, although it concerns information

from a number of different sources that include

touch# $he final section considers the

findings in relation to intersensory information%and loo"s at implications of the findings

for theoretical descriptions#

Some $heoretical 9onsiderations

Models of memory have often relegatedthe modality of inputs to a very minor role#

Some e1uate modality!specific information

solely with brief persistence of stimulation

after its offset% which has no function in memory



except that of initial registration# .rocessing

is carried by a short!term memory

system that is strictly limited in attentional

capacity# $he number of serial items towhich it can attend depends crucially on recoding

the inputs into more economical

forms &Miller% >FC'# @ favoured description

for many years was of fast!fading tracesof the stimulation that must be translated

1uic"ly into verbal form% in order to be

maintained in limited!capacity short!term

memory% prior to being stored in longertermmemory &e#g# @t"inson G Shiffrin%

>C'#

$he most influential recent model is a

+wor"ing memory, system which has severalcomponents &=addeley% >'# *t assumes

a central executive% decision!ma"ing

process that allocates attentional resources#

@ speech!based articulatory loop refreshes

fast!fading phonological &heard' inputs throughrehearsal &=addeley% >C% >/

=addeley G Hitch% >74'# @ +visuo!scratchpad, accounts for findings which show that

memory for spatial location% direction and

shape is disrupted more by conflicting visuo!

spatial than by verbal information% andfor evidence that such non!verbal information

can be maintained actively in memory

over short delays &e#g# @twood% >7>/ =roo"s%

>C/ Hitch G Halliday% >I/ Hitch etal% >/ Josslyn% >/ Josslyn et al%

>7/ Millar% >7Ka/ Segal G :usella% >7/

Shepard G 9ooper% >K/ Shepard G :eng%>7K''#*t is noteworthy that the main burden of

maintaining phonological information in

temporary memory is assigned to speechbased

output activities% rather than to inputcoding &e#g# =addeley% >C/ >/ =roadbent%

>4/ 9onrad% >C4/ Monsell% >7'#

$here is ample evidence that concomitant

speech% including mouthing of an irrelevantsyllable% disrupts recall for heard speech# *t

has been much more difficult to demonstrate

temporary memory for modality!specific

input sounds# =etter recall of the last item ina heard than viewed series &e#g# Aaugh G

Lorman% >CF' is sometimes attributed to

the persistence of the last sound in uncoded

&+raw,' +echoic, form# $he notion of precategoricalacoustic storage subsumes suffix

effects in which an irrelevant speech

sound at the end of an auditory se1uence affects

recall of the whole series# However% phonological effects in memory have also



been found when speech output is made difficult%

or is impossible &e#g# =esner% >7/

<allar G =addeley% >K'# @rticulation rate

is related to the si(e of immediate memoryspans &e#g# =addeley% >/ Hitch G Halliday%

>I/ Hitch et al% >% Hulme G $or!SUS,)), M(--,

Psicothema, 1999 74doff% >'# =ut age differences in span are

not eliminated by e1uating articulation rates%

as would be expected if speech output

were the only factor &Henry G Millar% >>%>I'# :amiliarity with input sounds has

significant effects on the si(e of immediate

memory spans with age &Henry G Millar%

>>'# <ery young children tend not to useverbal rehearsal strategies &e#g# 9onrad%

>7>'% but their memory span for sounds increases

nevertheless to some extent# $he

contribution of longer!term memory to input

coding for temporary memory is% therefore%a further factor that has to be included

in theoretical models &Henry G Millar%

>I'# :amiliarity with inputs% as well aslin"s with output systems thus need to be

considered in examining findings on touch#

3xperimental evidence for temporary

memory for visual inputs has been even moredifficult to establish than for sounds# <ision

does not seem to have such an obvious

closely!"nit output system as vocalisation

for hearing% though gestures in pointing% reaching%drawing and locomotion constitute

such output systems# However% the +perception!

action, models% deriving from Bibson

&>7'% which stress input!output lin"s% usethese to explain perceptual organisation without

recourse to memory processes# *n studies

of visual memory% on the other hand%

the main controversy centred on the 1uestionwhether visual memory is visual% or

spatial and +abstract, in character# $he visual

character of introspectively vivid visuo!

spatial imagery seems obvious to thosewho experience it# Moreover% errors in +reading

off, from very vivid or +eidetic, imagery

show that it involves memory rather

than persistence of +raw, sensory stimulation&Haber G Haber% >C4'# 3xperimental

findings have also been interpreted in analogy

with a transitory 1uasi!+pictorial, visual

buffer that functions as if in +a medium, of coordinated space &e#g# Josslyn%

>% >>'# =ut experiments have not always

distinguished between visual and spatial

aspects of the materials# Discrepant visual



inputs that interfere with memory for

visual presentations may do so because of

their spatial form% and not because they are

visual in character &e#g# 0ogie% >C/ 0ogie%ucco G =addeley% >'# $hus% evidence

that simple flashes of light have relatively

little effect on memory for visuo!spatial information

has suggested that memory dependson +abstract, spatial representations#

$he notion implies that representations in

memory are either not specifically visual in

character &introspective reports are mista"en'%or that their visual character is functionally

irrelevant% or both#

Levertheless% the total burden of current

evidence suggests that temporary memoryfor modality!specific visual aspects% as well

as for their spatial organisation% may be assumed#

$he fact that electrical stimulation

of visual areas of the brain produces visual

images &e#g# Dobelle% Mlade)ovs"y G Birvin%>74'% and cognate evidence for the involvement

of the visual cortex in attemptsto form visual images &Boldenberg et al%

>'% suggests a physiological basis for

+visual, aspects of introspectively reported

imagery# Ahether or not that is sufficient toestablish that the visual character of reported

visual imagery is biologically useful% is

a moot point# =ut further experimental studies

with children and adults also strengthenevidence for temporary memory for specifically

visual aspects% as well as for spatial information

&e#g# 0ogie G =addeley% >/0ogie G .earson% >7'# $hus% recognitionas well as recall for visual patterns was better

than memory for se1uences of movements

to spatial targets% and the difference

varied with age &0ogie G .earson% >7'#$a"en together% the findings suggest a somewhat

more complex picture of +wor"ing

memory, than the original notion of shortterm

memory as a single system with one limitedattention bottlenec"#MEMO' () *OUC+

7F Psicothema, 1999

@n alternative has been to assume completely

distributed storage systems with multiple%separate +processing modules,% each

with its own temporary storage capacity

&e#g# Monsell% >4'# *n principle% modalityspecific

aspects of memory could easily beaccommodated in such a system% though that

was not the reason for the notion# $he extreme

version assumes 1uite separate +modules

, for different cognitive processes &:odor%



>I'# *t was originally ta"en up with great

alacrity% because the considerable functional

specialisation of different areas of the brain

seemed to accord better with descriptions interms of separate +modules, than with the

idea of one over!arching cognitive system#

$he evidence for regional cerebral specialisation

of functions is not in doubt# However%the physiological and psychophysiological

evidence neither re1uires% nor is actually

compatible with the assumption that there

are only very limited interactions betweendifferent brain regions &e#g# S1uire% >7'#

*t can be argued% on the contrary% that the

findings on specialisation of functions are

better described in terms of the convergence%in different combinations for different

regions% of processing paths or activities arising

from specialised analyses# @ more dynamic

picture of this "ind seems to be re1uired

particularly to account for evidenceon memory processes in touch#

$ouch has been comparatively neglectedin studies of psychology# $he issues that have

been considered here so far were raised

predominantly by findings with visual and

verbal materials# How do findings on touchfit in with these? seful general theoretical

models should account for findings on

touch as well as on vision and hearing# =ut

it is not sufficient to give theoretical descriptionsonly at the most general level# $he

1uestion is what forms of information can

be assumed to be available for processing intactual conditions% and what% if any% effectsthese have on memory#

$he point is that +touch, is actually a

euphemism for intersensory processing of

information from a number of different sources#$he s"in receptors convey information

about texture% pressure% temperature and

pain% as well as light touch% and the inputs

occur in various combinations &e#g# Jat(%>KF'# Moreover% even passive touch can depend

on concomitant input from proprioceptive

sources# Single unit recording has

shown that discrimination of round and rectangular ob)ects held in the mon"eyNs hand

depends on converging inputs from touch receptors

in the palm and proprioceptive inputs

from the posture of the finger )oints &Sa"ataG *wamura% >7'# $he organism

1uic"ly adapts to passive touch or pressure#

3ven passive perception usually needs intermittent%

necessarily se1uential% stimulation#Movement is crucial for active tactual exploration



to gain information about ob)ects

and environments &e#g# Bibson% >CK/ Eeves(%

>F'# $he term +haptics, was used to

designate that proprioceptive and "inaestheticinputs function together with touch in exploring

ob)ects &Eeves(% >F'# Bibson

&>CC' made the important point that the

modalities of vision and hearing% as well astouch% are perceptual systems which depend

on several sources of information#

However% in touch or haptics the combination

of inputs from different sources doesnot seem to operate as an inherently tightly

organised single perceptual system# 3xploratory

s"ill% experience with the stimulus ob)ects

and with tas"s% as well as physical characteristicsof stimulus ob)ects determine

haptic movements and performance &e#g#

@ppelle% >>/ =erla G =utterfield% >77/

Davidson% >7K'# $he combinations of converging

information% from touch% finger%hand and arm movements% but also proprioceptive

inputs from hand andor body postures%differ not only with tas" demands% but

also with the si(e% depth and composition of

ob)ects in touch &Millar% >>b% >4% >7'#SUS,)), M(--,

Psicothema, 1999 7F>3vidence on whether% and if so how% the

various modality!specific aspects of haptic

tas" conditions affect memory is considered

in the next section in relation to temporaryor +wor"ing, memory#

Short!term tactual memory

3vidence for modality!specific tactile

short!term memory was found in a studywhich demonstrated a tactile suffix effect

&Aat"ins G Aat"ins% >74'# Eecall of the

serial position in which fingers of both

hands had been touched was disrupted by astro"e across two fingers at the end of a series#

$he finding was interpreted as evidence

for capacity!limited tactile memory% analogous

to suffix effects in auditory memory&see earlier'# =ut the finding raises similar

1uestions as demonstrations for visuo!spatial

inputs# $hus% it is possible to argue that

recall of the se1uence in which fingers had been touched depended on coding the spatial

location of the fingers that had been touched#

*n principle% finger locations can be

coded spatially by reference to body!centredframes% in the absence of vision% and

even if covert visuo!spatial strategies were

not being used# Memory may% therefore% have

depended on the spatial organisation of



the tactual inputs% rather than on memory

for +feels,#

Millar &>7F a' showed that modalityspecific

tactual effects could be separatedexperimentally from verbal recoding of the

inputs# Eecall spans were compared for lists

of braille patterns which were either similar

tactually% or had similar sounding names% or were dissimilar on both counts# Sub)ects

were congenitally totally blind children at

different stages of learning braille# $hey felt

the patterns se1uentially in each list# $hetas" was to point to the serial position that a

subse1uently presented test pattern had occupied

in the memory series# Eesults for the

tactually similar lists were completely theopposite of those for phonologically similar

lists# @s expected from 9onradNs &e#g# >C4%

>7>' wor" with nameable visual items%

Millar &>7F a' found that recall spans for

patterns with phonologically confusable nameswere significantly impaired compared

to patterns with dissimilar names% showingthat the items had been recoded verbally#

$he difference related significantly% not

only to the si(e of memory spans on control

lists% but also to pre!test naming speeds for the items# Sub)ects with faster pre!test naming

latencies showed larger recall spans

and were more impaired by phonological similarity#

=y contrast% tactual similarity effectswere associated with small recall

spans% and related inversely to pre!test naming#

$actual similarity impaired recall more by sub)ects with smaller recall spans whoshowed little or no phonological similarity

effects% and were either slow on pre!test naming

or could not name the items on pretest#

3vidence that tactual similarity affectsthe si(e of recall spans suggests temporary

memory for tactual aspects of the items# $he

study has been described in some detail

again% because it is possible to rule out explanationsin terms of visual% as well as phonological

strategies% since the sub)ects were

congenitally totally blind# =ut that does not

mean that tactual memory effects are confinedto blind children# =lindfolded sighted

young children were tested on recall spans

for lists of tactually presented ob)ects# $he

ob)ect series were again either similar in feelor had similar names &Millar% >7F b'# @s

for the blind% tactual similarity% but not phonological

similarity reduced the recall spans

of children with small spans in control conditions%while sub)ects who achieved large



spans in control conditions were significantly

affected by phonological and not by

tactual similarity in the memory lists# Several

subse1uent studies also showed that thefindings could not be attributed to indivi!MEMO' () *OUC+

7FK Psicothema, 1999

dual difference factors% such as age &Millar/>7 a%b'# $hus% the same children who had

recall spans of six or more tactual items that

they could name% and improved further

when the items were grouped% produced recallspans of only two to three items for tactual

nonsense shapes# *f anything% grouping

tactual nonsense shapes had the opposite effect#

$he findings thus suggest that modality!specific tactual memory must be assumed%

but it typically consists of only two to

three tactual items#

.rima facie% there seems to be no reason

why memory spans for tactual patternsshould be worse than for the same patterns

in vision% if the tactual patterns are coded

spatially as global shapes# 3vidence for spatialcoding comes from studies of brain insults

in specialised cerebral regions that are

"nown to be important in visuo!spatial organisation

&e#g# right hemisphere% post!parietalarea'# Such infarcts also disrupt temporary

memory for nonverbal tactual inputs

in spatial tas"s% although it is not always

clear whether the loss is primarily sensoryor attentional &e#g# Stein% >>'# =ut there is

good evidence that spatial tas"s involve a

number of cortical and subcortical regions

of the brain# $he involvement of differentregions &e#g# hippocampal% sensori!motor%

somatosensory% pre!frontal% post!parietal%

cerebellar% occipital and temporal' seems to

depend on the combination of demands thattas"s ma"e on spatial% verbal and cognitive

and memory s"ills% and on biomechanical

constraints that particular conditions involve#

Spatial tas"s generally show greater involvementof the right hemisphere% whether

the stimulus materials are visual or tactile#

However% it is not possible to ma"e the reverse

inference% and to conclude that a lefthandadvantage necessarily involves right

hemispherespatial processing# Similarly%

without additional evidence and ade1uate

tas" analysis% a right hand advantage doesnot necessarily imply left hemisphereverbal

processing# $hus% braille studies have

reported left hand advantages% right hand

advantages% and e1ual performance by both



hands# Lot surprisingly% the studies differ

widely in the type of braille tas" that was

being used% and in the experience and s"ill

of the sub)ects who too" part# Moreover% someapparently spatial tas"s% such as aiming%

have produced right hand advantages &Millar%

>4% for review'# $o ma"e sense% stimulus

conditions% tas" demands% and sub)ectsNexperience with exploratory strategies

and materials have to be ta"en into account

&e#g# Ail"inson G 9arr% >7'#

$here has long been evidence that memoryfor unfamiliar tactual shapes is much

less efficient than memory for the same unfamiliar

shapes in vision &e#g#/ =erla G =utterfield%

>77/ Bilson G =addeley% >C/Boodnow% >7>/ Millar >7>a% >77a%

>7b% >% >>'# Such assertions are often

misunderstood# *t should be stressed at

once% therefore% that they do not% of course%

call in 1uestion that shape +can, be perceived by touch# $hat has long been established

&e#g# Bibson% >CK/ Jat(% >KF'% and re1uiresno further research# Lor should evidence

of poor tactual recognition be ta"en

to mean that memory must necessarily be

poor when the inputs are tactual# :or instance%tactual recognition of familiar three!dimensional

ob)ects is often very good &e#g#

Hatwell% >7/ Jat(% >KF/ Jlat("y% 0ederman

G Met(ger% >F/ Aeber% >I4% transl#>7'# 0evels of efficiency% whether high or

low% are of theoretical interest only because

they raise 1uestions about the factors that produce differences# $he 1uestion here isthus about the informational conditions that

underlie relatively small spans and poor memory

for tactual inputs#

$hus% it is relevant that poorer tactual recognitionis more often found for unfamiliar

two!dimensional raised line and raised!dot

patterns% early in learning &e#g#/ Boodnow%

>7>/ Hatwell% >7/ 0ederman% Jlat("y%SUS,)), M(--,

Psicothema, 1999 7FI

9hataway G Summers% >/ Millar%

>7Fa%b% >77b% >7a/ >Fa% >% >>'%

rather than for familiar ob)ects &see earlier'%and for three!dimensional shapes &Davidson%

=arnes G Mullen% >74/ Jlat("y et al%

>F/ Millar% >74/ Shimi(u% Saida% G Shimura%

>I'#$he difference is not merely that solid

forms% as such% necessarily provide more

general information than outline shapes% as

has sometimes been assumed# Many studies



of I!D shapes use familiar ob)ects# :or the

recognition of such ob)ects% shape &e #g#

long versus round' is merely one among

many possible cues% from temperature to resilienceto pressure% to the use% name and

contextual meaning of the ob)ect &see earlier'#

$he important advantage for recognising

the shape of unfamiliar I!D versus K!Dforms is that I!D shapes potentially afford

more reference cues for spatial coding# $hus

both hands are usually used to manipulate

small three!dimensional forms# $he twohands can act as spatial anchors and reference

frames in relation to each other to

locate component features# :or large% stationary

three!dimensional ob)ects that are explored by hand and arm movements% contour

features can be located and spatially organised

by reference to body!centred reference

frames# $wo!dimensional raised line

configurations are usually explored byone finger% and% in particular if they are

small% are difficult to relate to body!centredframes#

Ae actually have sufficient evidence

from past findings to be able to specify the

main types of information that can vary intas"s that demand tactual memory for shape

or form# .revious experience% both with and

without vision% affects performance significantly#

Modes of exploration and movementsvary with familiarity% and with the type%

si(e% depth and composition of stimuli#

$hese% and tas" conditions are among themost important variables in haptic tas"s&Davidson% >7K% >74/ Davidson et al%

>74/ 0ocher G Simmons% >7/ Millar%

>>% >a/ Simmons G 0ocher% >7'# @

crucial factor is the type% amount and convergenceof reference information that is

available from internal and external sources%

since it determines the spatial organisation

of shapes in haptic conditions &=ertho(%>>/ Millar >>a% >% >4/ .aillard%

>>'#

$hus% the informational conditions in

memory tas"s for unfamiliar tactual raisedlineand raised!dot patterns are typically

characterised by a paucity of the reference

cues that are needed for the patterns to be

spatially organised as global shapes &Millar%>7 a% >a% >4% >7'#

=raille patterns are an important example#

$he patterns lac" salient features% because

all characters derive from a single%small &C#K x K mm' matrix of six raised dots#



$he small si(e produces problems of acuity#

=ut the principal difficulty does not lie in

distinguishing patterns from each other#

Discriminating characters is fairly easyeven for the inexperienced &Jat(% >KF/ Millar%

>77a%b'# $he main problem lies in the

paucity of reference cues for coding the patterns

as global shapes# $he lac" of redundancymeans that there are no salient features

in the patterns that relate easily to each

other# $hat ma"es it difficult to code the pattern

as a distinctive global spatial configuration#*t is also difficult to use self!referent

frames to code the pattern as a global configuration%

because the components are also

too small to be related to body!centred referencecues to determine their position in

the pattern# *n principle% the tip of the exploring

finger could act as a frame in relation

to which dot locations could be determined#

However% that re1uires some experience#*nexperienced people tend to +rub,

over the dots too unsystematically to benefitfrom that# 3xternal reference cues are typically

lac"ing in blind conditions% unlessMEMO' () *OUC+

7F4 Psicothema, 1999

they are deliberately sought# $his is in contrastto visual conditions% which typically

provide concomitant reference% anchor% and

updating cues which organise visual patterns%

including braille shapes% automaticallyas distinctive global configurations#

$he efficiency of visual shape recognition is

reduced to the level of touch when the field

of view is restricted so that simultaneous attentionto the components of a pattern is no

longer possible &e#g# 0oomis G Jlat("y%

>>'# *n touch% reference cues% for coding

patterns as global shapes% re1uire explorationand movement# 3ffective exploratory

strategies are learned with experience &e#g#

=erla G =utterfield% >77'#

*t is thus possible to explain the evidencefor small tactual memory spans and poor recognition

of unfamiliar tactual shapes% as a

direct conse1uence of the paucity of reference

information in tactual conditions% because that ma"es it difficult for inputs to

be spatially organised in terms of global

configurations &Millar% >7 a'# Blobal shape

can be regarded as an extremely economicalorganisation of inputs to the system#

9oding in terms of shape can thus perform

the important function of information reduction#

$he explanation har"s bac" to MillerNs



&>FC' contention that immediate memory

spans are limited% and that inputs re1uire

recoding in economical form% if capacity

is not to be exceeded#3vidence that% early in learning% small

raised dot patterns tend to be coded by texture

or dot!density cues% rather than in terms

of their global outline shape has been reviewedextensively before &e#g# Millar% >7a%

>>a / >7'# =riefly% the findings come

from a number of studies that used convergent

methods to test for shape coding intouch# $hus% generalising braille characters

to enlarged forms was found to depend on

experience with the characters# Poung beginners

needed training to recognise enlargedforms of braille characters that they had

learned to name# 9hildren with more experience

generalised to enlarged forms without

error% although it too" them longer to

recognise letters in enlarged form than inthe original format &Millar% >77 a#'# 3rrors

consisting of missed dots are the most prevalent&Lolan G Jederis% >C'# Outline

shape is a poor cue for braille letter recognition

since several letters share the same

outline# .riming patterns with connectedoutline shapes produced poorer rather than

better recognition% and errors in recognising

and in reproducing patterns were found to

depend on failures to locate the position of constituent dots accurately% rather than on

confusing outline shapes &Millar% >7a%

>Fa'# =lindfolded sighted children foundit very easy to discriminate between braillecharacters that they had never felt before#

=ut their drawings of four patterns that they

learned subse1uently showed that they had

no idea of the shapes of the characters% suggestingthat the global shapes of the patterns

had not been the basis for their accuracy of

discrimination &>77 a'# Matching successive

patterns by dot!density differences wassuperior to matching by the spatial location

of the dots% and dot!density differences produced

higher levels of performance than

matching by symmetry versus asymmetry inthe shapes &Millar% >7 a'# Differences in

dot numerosity were also a better cue also

than outline shape for )udging the odd one

out of four braille words &Millar% >4a'#Dot!density differences were also superior

to differences in outline shape for matching

small dot patterns other than braille &Millar%

>F a'# Eecognition of braille letters wassignificantly impaired when the characters



differed from each other in texture &dot!gap

intervals'% despite the fact that they were

identical in shape% as well as in name &Millar%

>77b'#$here is% of course% no 1uestion that even

the small braille patterns that lac" redundancy

can be coded as spatial configura!SUS,)), M(--,

Psicothema, 1999 7FF

tions also by touch# $hat usually re1uires

prior experience# Direct evidence comes

from filming the movements of the readingfinger from underneath transparent surfaces

&Millar% > b% >7''# Deliberate exploration

of characters for shape information is

seen typically in very slow% letter!by!letter readers% particularly by former print readers

with extensive visuo!spatial experience%

who learned braille relatively late in life

&Millar% >7'# $hey move the exploring

finger in updown% (ig(ag and circular fashionover a character in attempting to construct

the total pattern# Such movements become

much faster and stereotyped with experience%without losing the typical character

of scanning the form# :or experienced

readers% the manner of coding depends on

tas" demands# :luent braillists who have learned braille from the start% show evidence

of coding letter shapes mainly in tas"s that

demand search for single characters# =y

contrast% fast reading for meaning is basedon cues from dynamic shear patterns across

the moving fingerpad &Millar% >7'# Aith

experience% scanning movements by the two

hands are organised% relative to each other%to provide the spatial information about the

location of words and lines that is needed

for reading texts% as well as the tactual &shear

pattern' information which is translatedrapidly into verbal &phonological and semantic'

form for comprehension and recall#

$a"en together% the findings support the

hypothesis that the small &two to three item'tactual memory spans for unfamiliar patterns

&see earlier' can be explained by the

paucity of reference information for coding

inputs spatially in these conditions# $ouchseems to be particularly good at feeling texture

differences# $hese can be used to enhance

discrimination &Millar% >C a / Schiff

G *si"ow% >CC'% and may underlie the modality!specific tactual coding that was demonstrated#

Eelying on texture differences

in memory when reference information is

too sparse for spatial organisation would



certainly be useful# =ut it would also explain

why non!verbal tactual memory spans

were confined to two to three items# $hat

was in contrast to large spans for inputs thatare 1uic"ly re!coded verbally via long!term

familiar names that can be rehearsed in the

short term &see earlier'#

$he hypothesis that spatial coding dependson the amount and redundancy of available

reference information can also account

for better recognition of I!D forms that are

not necessarily nameable# Such conditionsexist% for instance% for experienced sub)ects

who use exploratory strategies that actively

see" environmental reference cues% or use the

two hands relative to the body midline to actas self!referent frames in relation to which

tactual +feels, can be localised#

*t should be noted that the term +frames

of reference, is used here as an operationally

defined term# $he relevant informationcan be experimentally manipulated#

=lindfolding eliminates current informationabout environmental frames in relation to

which the location of a stimulus can be determined#

Such manipulation leaves bodycentred

reference frames intact# =ut self!referentframes can also be enhanced or disturbed#

Self!reference that is centred on the

body midline can be disrupted by changing

the posture or orientation of the body% or theorientation of displays &e#g# Millar% >7Fc%

>F b'# Similarly% stimuli can be aligned to

facilitate self!referent coding# Ae showedthat positioning the two exploring fingersdirectly above the stimuli% in alignment with

the body midaxis% produced a similar advantage

for symmetric over asymmetric

&raised line' patterns to that which is foundin vision &=allesteros% Millar G Eeales%

>/ Millar% =allesteros G Eeales% >4'#

=y contrast% shape symmetry is not an effective

cue in haptic conditions that affordfew reference cues for spatial coding &Millar%

>7 a'# 3xploring unfamiliar shapesMEMO' () *OUC+

7FC Psicothema, 1999

blind with one finger% without special alignmentto the body!centred frames provides

few references cues# *n such conditions%

symmetry has no advantage &=allesteros%

Millar G Eeales% >% Millar% =allesterosG Eeales% >4/ Millar >7 a'#

Eeference frames in relation to which the

location of tactual features can be determined

are needed for spatial coding# $he hypothesis



here is that spatially organised configurations

reduce inputs% without loss of information%

to a form in which the information

is manageable in memory over theshort term# *t predicts good memory for spatially

organised tactual inputs in contrast to

relying on relatively unorganised texture aspects

of tactual input#Studies concerned with nonverbal tactual

stimuli have mainly used single stimulus

configurations that are larger than braille

patterns &e#g# Aarm G :oul"e% >C/ 0ocher G Simmons% >7 '# $he next section focuses

more specifically on factors in memory

for the somewhat larger movements that

such layouts re1uire#Short!term memory for movements

Movements have mainly been studied as

output systems# $he focus has been on the

"ind of control &feedbac"% feed!forward%

open!loop or closed!loop' that accounts for controls in sensorimotor and motor s"ills#

However% recent wor" has emphasised theimportance% as well as the diversity% of reference

frames in relation to which movements

are organised spatially &e#g# =ertho(%

>>/ Qeannerod% >% >>/ .aillard%>>'# Most of the wor" has concerned movements

in visual environments in which

the goal or target and other external cues

were visible% either throughout the tests% or initially and at various points before blindfolding#

@ good deal of the evidence on spatial

coding% for instance% of reaching movements%comes from studies with blindfoldedsighted sub)ects who were initially allowed

sight of the target# $he information sub)ects

have at the beginning of the tas" was thus of

the target location that could% in principle% be determined in relation to surrounding external

visuo!spatial frame cues% as well as

relative to body!centred cues# Ahen external

frame cues are excluded by blindfoldingsub)ects% the postural% body!centred frames

that guide reaching and aiming movements

sustain memory for the target location# *n

totally blind conditions% external environmentaltargets can be signalled initially by

auditory or olfactory cues to which postures

are ad)usted#

Short!term memory for blind movementswithin personal space &reach' has also been

studied in the context of attentional or capacity

limitations &0aabs G Simmons% >>'#

0aabs &>7I' distinguished between codinglocation and movement or "inaesthetic information



by re1uiring recall of either the

location or the extent of a positioning movement%

from a different position than in

presentation# *n such paradigms% the endlocationis recalled much more accurately

than the extent of the movement# $he findings

were widely interpreted to suggest

that movements and spatial location are codeddifferently in short!term memory &Jelso

G Aallace% >7/ Jelso G 9lar"e% >K/

0aabs G Simmons% >>/ Marteniu"% >7/

Eussell% >7C'# $hus the endlocations of blind movements can be coded spatially by

reference to body!centred spatial frames%

while recall of movement extents depends

on "inaesthetic inputs when these are notorganised relative to spatial anchors or frames#

$here has long been evidence that

even unorganised movements survive in

short!term recall# $hus% interpolating different%

irrelevant movements in delay periods%distorts recall of the target movement significantly

&@dams G D)i"stra% >CC'#Eecall of endlocations and of movement

extents of positioning movements is notSUS,)), M(--,

Psicothema, 1999 7F7

completely independent in paradigms inwhich recall starts from a different position

&e#g# Aalsh and Eussell% >7% >'# $hus%

sub)ects undershoot endlocations if the start

in recall is further away% and overshoot if the start location is nearer than the start in

presentation# .recisely the opposite pattern

of over!and undershooting is found in recall

of movement extent or distance from positionsthat are further away or nearer than the

original starting point of the movement

&*mana"a% G @bernethy% >K a'# *t has been

suggested that sub)ects use a locationstrategy when location information is reliable%

but use other means% such as trying to time

movements by counting% when location

is unreliable &e#g# Diewert G Eoy% >7'#3xplicit information about starting and endpositions

of a movement enabled sub)ects to

use a +location, strategy which abolished

the typical over!and undershooting patterns#$he typical pattern reappeared when that location

was made unreliable and sub)ects

were as"ed to use counting &timing' or to

envisage the distance from a changed positionabout which they had no information

&*mana"a G @bernethy% >K b'# $he findings

can be explained in terms of coding

endlocation spatially% and relying on memory



for "inaesthetic cues% depending on

the reliability of the spatial information#

3xternal frame information can also be

provided% and its use encouraged by instructions%in blind conditions# $hus deliberately

providing an external frame% and instructing

blindfolded sighted children to use it to remember

the endlocations of positioning movementsfrom different starting points% produced

greater accuracy% and significantly reduced

interference from changes in the

length of movements &Millar% >F b'# Deliberatelyinstructing the sub)ects to use their

body midline as a spatial anchor had similar%

although less dramatic effects#

*t has been shown that reliable spatial informationdoes not need to be visual in origin#

9oding locations spatially relative to

egocentric frames has been demonstrated

with young congenitally totally blind children#

*ndeed% young congenitally totally blind children tend to rely more on bodycentred

spatial coding &Millar >> b% >F b'# Such spatial information is% of course%

reliable also in the absence of vision# Ahen

self!referent cues are unreliable and there

are no salient &or well!"nown' external framecues% they tend to use memory for movements

&Millar% >7Fc% >7'# sing a cognitive

interference tas" &counting bac"wards'

in con)unction with the 0aabs &>7I' paradigm% we found that congenitally totally

blind children showed interference in

memory for locations that could be codedreliably by reference to body!centred frames%

but no interference in memory for movements%

when reference cues were unreliable

&Millar% >4% p# >4'# Memory for locations

that could be coded reliably by referenceto body!centred frames showed significant

interference by the difficult cognitive

tas" during delays% while such tas"s did

not interfere with memory for movementsthat could not be coded reliably in terms of

spatial locations#

$he findings thus demonstrate short!term

memory for movements also in the total absenceof visual information# =ut they suggest

also that memory for movement extents%

coded in terms of the "inaesthetic inputs%

tends to be less accurate and more variablethan movement information about the

endlocation if these are coded spatially% for

instance% with reference to body!centred

frames#Spatial coding is not the only form of organising



movement information# =lind children

are taught to estimate distances by

counting the number of steps% or sounds of a

turning wheel# 9ounting during delays has been found to impair "inaesthetic memory

&Ailliams% =eaver% Spence G Eundell%

>C'# =ut the degree of practice is also im!MEMO' () *OUC+

7F Psicothema, 1999

portant# 9onstant repetition of a given movement

distance interfered significantly

with memory for endlocations of the movementwhen the starting position of these varied

&Millar% >F b'# $hus% with extensive

practice% memory for movement extents can

become extremely robust also# $he whole1uestion of effects of familiarity on shortterm

memory spans and on wor"ing memory

is extremely important% not least for

the recall and recognition of movement information%

and will be considered in moredetail later#

$he point that needs to be stressed is that

short!term memory for "inaesthetic inputscan be demonstrated even when these inputs

are not spatially organised% although memory

for unorganised "inaesthetic inputs

&e#g# movement extent' is less accurate andless stable# Ae have shown modality!specific

motor memory in blind conditions from

which any influence from longer!term visual

"nowledge can be excluded &Millar G*ttyerah% >>'# Eecall of a criterion movement

by congenitally totally blind children

showed signficant overshooting when an

irrelevant larger movement was interpolatedduring the delay period% and significant undershooting

of the criterion in recall when

the interpolated irrelevant movement was

shorter than the criterion# =lindfolded sightedchildren showed the same effects# =ut in

the case of the blind children it was also

possible to exclude any possibility that the

modality!specific effects on short!term memorycould have been mediated by longerterm

visual "nowledge#

.erhaps more important still% merely

imagining the irrelevant movements duringthe delay period% without actually executing

them% had similar effects on short!term recall

of a criterion movement as actually excecuting

the irrelevant movement &Millar G*ttyerah% >>'# Such movement imagery

was shown also in conditions of total blindness#

9ongenitally totally blind children% as

well as blindfolded sighted children% were



instructed to imagine &+in their heads,' executing

an irrelevant shorter or longer movement

during the delay before recalling the

criterion% but not to ma"e the movementsovertly# Significant undershooting and

overshooting in recall% depending on the type

of irrelevant movement that had been

imagined% was shown by the congenitallytotally blind as well as by blindfolded sighted

children#

$he finding shows movement representation

in short!term memory# $his is an importantfinding% because it suggests a basis

for mental rehearsal of movements even in

conditions that exclude past as well as present

visual information totally# Mental rehearsalof movements has long been shown to

improve performance by sighted adults &e#g#

Qohnson% >K'% and is used in sports training#

$he effects of imagining irrelevant

movements with blind children thus suggestthat such strategies are% in principle% also

available in totally blind conditions# *nstructionsto mentally rehearse the criterion

movement &+imagine repeating the movement

in your head,' during delays significantly

improved recall by the blindfoldedsighted children# $he improvement was in

the same direction for the congenitally totally

blind# =ut it did not reach significance

level% despite the fact that discrepant movementsduring delays significantly interfered

with their recall &see earlier'# $he lac" of

significant improvement is probably explained by differences in informational conditions#@ll movements in the study had been

designed to cross the body midline% in order

to encourage movement coding by reducing

spatial coding in terms of the body midline&Millar G *ttyerah% >>'# Poung blind children

tend to rely on memory for movements

when coding in terms of self!referent spatial

frames is made difficult or disrupted &Millar%>7% >>b% >Fb% >4'# Memory

for the criterion movement would be liableSUS,)), M(--,

Psicothema, 1999 7F

to disruption by the discrepant interpolationsin delays if the criterion was coded in

terms of "inaesthetic cues# =ut such coding

may not be sufficiently economical to sustain

active mental rehearsal to improve recall#Eehearsal strategies are li"ely to be

more efficient with codes that organise inputs

economically &see earlier'# $hus the

blindfolded sighted may be able to use additional



reference frames% derived from visuo!

spatial experience% to organise "inaesthetic

inputs when self!referent spatial coding

is made difficult# 3ffective mental rehearsalof "inaesthetic cues may depend on

using more economical codes that reduce

the memory load of "inaesthetic inputs#

Spatial coding% either in terms of body!centredor external frames% would produce better

recall for that reason#

Mental rehearsal of movements can be

shown to have physiological correlates#$hus physiological studies of motor imagery

have shown that patterns of activity in

brain areas% including the motor cortex% are

similar to patterns for actually executed movements&Qeannerod G Decety% >F'# *t

may be important that sub)ects in most movement

studies are sighted people who are

tested blindfolded# *n some cases% testing

occurs in the dar"% but an external orientingcue remains visible throughout# *t seems

possible that in conditions of total blindness%efficient organisation of movements%

which permits effective mental rehearsal%

re1uires more practice% familiarity and conse1uently

more influence of longer!term"nowledge for mental rehearsal of movements

to produce the same level of facilitation

in short!term memory# $hat re1uires

further study#$he whole 1uestion of longer!term memory

involvement in short!term and wor"ing

memory is extremely important% not leastfor the recall and recognition of movementinformation# $here is little doubt that

immediate memory spans are larger for familiar

than for new words% and for tactual

patterns for which names can be retrievedeasily and fast &e#g# Henry G Millar% >>%

>I/ Millar% >7Fa'# *t seems li"ely that

this is true also for immediate memory for

movements# Many everyday movementsare% of course% so well practiced that they

run off automatically with great precision#

@ discussion of the feedbac" and feed!forward

processes by which movement accuracyis achieved is beyond the present brief#

$he point is rather that short!term motor

memory in blind conditions can be based on

"inaesthetic inputs% but that efficient mentalrehearsal of movements% which facilitates

recall% involves longer!term memory for efficient

means of organising the input information

so as to reduce its memory load#$he longer!term information that * have



particularly in mind% as one basis of shortterm

memory for movement inputs% are

practiced exploratory movements# $he importance

of input!output lin"s for mental rehearsaland the si(e of immediate memory

spans has been mentioned before in connection

with memory for sounds &see% Henry G

Millar% >>% >I'# =ut there is also evidencesuggesting that familiarity with wellorganised

exploratory movements form an

important basis of tactual recognition memory#

$hus% a surprising finding in getting congenitallytotally blind children to draw was

that that even though they had never drawn

before% the older sub)ects at least drew figures

that differed little in general schemafrom those of their sighted cohorts &Millar%

>7F c'# More surprising still% the blind children

were much better at producing recognisable

raised line drawings of the human

figure than at recognising such figures &Millar%>C b% >% >> a'# :or the sighted%

the reverse is the case# Poung sighted childrencan recognise drawings long before

they can attempt to reproduce them# $he

finding for the blind should not% of course%MEMO' () *OUC+

7C Psicothema, 1999

be ta"en to mean that they never recognise

drawings immediately% let alone that such

recognition is impossible# =ut it does re1uire

more familiarity with exploratory strategiesthan is needed in vision#

$he reversal in difficulty between recognition

and production focuses attention on

the importance of both movement output%and familiarity with exploratory strategies%

as factors in short!term motor memory# $he

findings suggest strongly that familiarity

with efficiently organised exploratory outputmovements can serve as% at least one%

important basis for haptic recognition and

short!term haptic memory in the total absence

of sight &Millar% >>'#*ntersensory coding and haptic memory

* have suggested that memory for tactual

information has to be examined in the context

of intersensory processing% in whichconverging inputs vary with tas" demands#

*n blind conditions% inputs for two!dimensional

stimulus patterns come from touch% movement%

and posture cues% in varying con)unctionswith longer!term procedural and

organi(ational "nowledge# $he findings that

have been reviewed here suggest how information

from touch and movement may be



coded in short!term memory% and what informational

conditions produce different levels

of efficiency in recognition and recall spans#

Lot surprisingly% general principles thatapply to short!term memory for inputs from

other modalities also apply to memory for

haptic inputs# One of the most important is

the principle of economy of coding &Miller%>FC'# =riefly% the more parsimonious the

organisation of inputs% the greater is the probability

of recall# $he principle implies that

there are limits to the amount of informationthat the organism can handle at any one time#

$he fact that such +capacity limits, are

not rigid is shown by the almost universal

effect of familiarity and repetition# :amiliarityeffects are also &though not only' important

in the modes of recoding% or reorgani(ing

inputs more parsimoniously% that are

available to a sub)ect# $he second principle

is% therefore% that tas"s% which re1uire temporarymemory% also involve longer!term

memory to greater or lesser extents#$he third principle% advocated here% is

that limits on short!term functioning depend

on the amount of overlap and redundancy of

converging information from different sources# Leither the metaphor of a single limited!

capacity channel% nor the notion of numbers

of 1uite separate &floppy!dis"!li"e' modules%

are ade1uate# $he alternative metaphor is needed particularly for increasing evidence

on the relation between the modalities#

:indings suggest that high degrees of speciali(ation% on the one hand% but alsohigh degrees of informational overlap% on

the other hand% are needed to organise inputs

spatially in terms of reference frames#

Multisensory information is indeed thenorm for humans in most conditions# *t is

inconceivable% on general grounds% that

multiple speciali(ed mechanisms would have

evolved if each provided precisely thesame higher order abstract information#

Speciali(ed series of analyses of inputs

from different external and internal sources

converge in varying combinations to providemultisensory information# $hus% the physiological

evidence shows that a number of

areas of the brain that subserve spatial tas"s

receive multisensory information &e#g#Stein% >>'# Single unit recording has

found bimodal neurons% which are activated

both by visual and tactual stimuli% in a number

of brain areas which are involved in reachingmovements% suggesting how spatial



organisation of reaching movements may be

encoded relative to extrapersonal space

&Bra(iano G Bross% >4% >F'# Multisensory

information and overlap seems to be particularly important for the spatial organisation

of inputs#SUS,)), M(--,

Psicothema, 1999 7C>3xperimental studies of crossmodal% visual

tactual performance have mainly used

paradigms which dissociate the contributing

modalities in spatial tas"s# $here is ampleevidence from these that viewing the hand

through distorting lenses alters sub)ectsN

haptic perception of where their hands are

&e#g# Howard G $empleton% >CC'# 9rossmodalcoding of I!D shapes has been demonstrated

with young children &e#g# Eudel

G $euber% >C4'# =ut it involves more than

one factor# $as" conditions% even the order

in which intramodal and crossmodal conditionsare presented% have signficant effects

&e#g# Millar% >7F c'# :ewer studies actually

use simultaneous bimodal inputs# =ut it isfairly clear from the findings that concomitant

inputs from different sources facilitate

performance particularly in conditions in

which the available tas" information is degradedor insufficient# $hus adding information

from touch to vision contributes little

to bettering visual shape recognition% but

adding visual information aids recognitionof unfamiliar tactual shapes &Millar% >7>/

Heller% >K'# Similarly% concordant inputs

from texture and shape cues improve tactual

performance% while discordant inputs disruptrecognition &Millar% >C c'# $he tas"s

that are of special interest here concern recognition

and memory of relatively unfamiliar

K!D shapes and displays# Such tas"s arerarely a problem in normal visual conditions

even for very young children &e#g# =allesteros

et al% >/ Millar% >7>% >7Ka/ Millar

et al% >4'# <isual conditions typically providethe concomitant cues from different

surfaces and features that act as reference

frames for spatial coding from the start# Moreover%

they usually overlap with convergent proprioceptive reference cues#

$he same tas"s for which vision provides

the most salient concomitant reference cues

can also be performed with purely haptic information#=ut the automatic overlap and

redundancy of concomitant current reference

cues from different sources is severely

reduced the absence of sight# *t is possible%



in principle% to achieve the same levels of

efficiency in haptic as in visual tas"s that re1uire

memory for K!D shapes% distances% directions%

or locations% as in vision% providedthat alternative means of reference are available

for spatial coding# @t the same time%

information conditions are not precisely the

same for blindfolded sighted sub)ects% as for the congenitally totally blind who have no

long!term visual experience &Millar% >7%

> a% >4'# =ody!centred reference frames%

prior procedural experience in searchingfor external frame cues% and cue redundancy

from alternative &e#g# hearing'

sources become more important for spatial

coding in these conditions#Memory for information from touch and

movement% both in short!term blindfolding%

and in the total absence of prior visual experience%

has been demonstrated# $he principle

of parsimony applies# Short!termspans for unfamiliar inputs are small# =ut

they show effects of coding texture &shear pattern' in the case of shape tas"s% and "inaesthetic

coding in the case of unfamiliar

movements% or both# Such memory coding

is +modality!specific, in the sense that codingis derived from relatively specific aspects

of the input#

More robust short!term haptic memory is

found when the same haptic inputs are spatiallyorganised# Such coding depends on

accessible reference frame cues% as does

spatial coding in visual conditions# $he samegeneral principle thus applies# Levertheless%the informational conditions on which

such coding depends differ from those in

which visual cues are also present# $hus

there is greater need to rely on body!centredreference information% or prior procedural

"nowledge% or to use alternative external

&e#g# sound' location cues when that is possible#

@lternative means of more parsimoniouscoding can involve naming &see ear!MEMO' () *OUC+

7CK Psicothema, 1999

lier'% or counting# Moreover% the findings

show that short!term haptic memory can involvemental rehearsal of movements# $his

differs from the articulatory coding that increases

verbal memory spans# Memory

even for the more organised haptic inputsthus includes information that derives from

the haptic input conditions# Memory in

touch thus includes +modality!specific, aspects

of the input information#



$o fit these findings into some form of

+wor"ing memory, model% one might add

a haptic ! movement loop system% in analogy

with articulatory coding# =ut to wor" effectively% the system would also need access

to longer!term visuo!spatial andor

egocentric reference information% as well

as to longer!term procedural "nowledge#Such access would need to be 1uite flexible%

especially in response to differences in

tas" demands# *t is possible that the assumption

of a +central executive, in thesystem &=addeley% >' might be sufficient

to fulfill that role# =ut it is not 1uite

clear how the model incorporates the continual

changes in longer!term memory thatmust be supposed with development and

further experience% and which clearly play

an important role% particularly in haptic

short!term memory#

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