a single-element impact in global/local processing: the roles of element centrality and...

Psychological Research (2008) 72:155–167
DOI 10.1007/s00426-006-0102-2
ORIGINAL ARTICLE

A single-element impact in global/local processing: the roles of element centrality and diagnosticity

David Navon

Received: 12 June 2006 / Accepted: 2 October 2006 / Published online: 23 January 2007© Springer-Verlag 2007

Abstract A modiWcation of the compound stimuli par-adigm has been used to measure the impact of a certainsingle element on the local-to-global eVect and to com-pare the measured impacts of central and non-centralelements matched on diagnosticity. In addition to glo-bal letters made of identical response-associated ele-ments, some global letters comprised of only oneresponse-associated element at a speciWc location (withall other ones being response-neutral), and in someother global letters that critical element was ratherresponse-neutral (with all other ones being response-associated). Experiment 1 showed that the contributionof a central element that served as a distinctive featurewas as large as the joint contribution of all other ele-ments. Experiment 2 (as well as Experiment 4) showedthat, in contrast, a non-central element that served as adistinctive feature did not contribute at all to the eVect.Experiment 3 showed that the contribution of a centralelement was still as large as the joint contribution of allother elements even when it was completely irrelevantfor selecting the response.

Introduction

The global precedence hypothesis about the course ofperceptual processing (Navon, 1977) has been put totest by exploring various eVects of global/local advan-tage in hierarchical stimuli often referred to as com-pound stimuli (e.g., Amirkhiabani & Lovegrove, 1996,

1999; Boer & Keuss, 1982; Enns & Kingstone, 1995;Fink et al., 1996, 1997; Grice, Canham, & Boroughs,1983; Han, Humphreys, & Chen, 1999; HoVman, 1980;Hughes, Layton, Baird, & Lester, 1984; Kimchi &Palmer, 1982; Kinchla & Wolfe, 1979; LaGasse, 1993;Lamb & Robertson, 1988, 1989, 1990; Lamb, Yund, &Pond, 1999; Lasaga, 1989; Martin, 1979; Miller, 1981;Miller & Navon, 2002; Navon, 1981, 1983, 1991; Navon& Norman, 1983; Paquet & Merikle, 1984, 1988; Rob-ertson, Egly, Lamb & Kerth, 1993; StoVer, 1993; Ward,1982; see Kimchi, 1992; for a critical review, Navon,2003, for a comprehensive commentary).

The sense in studying global/local advantage by par-adigms employing compound stimuli depends a lot onmaking globality levels as comparable as possible. Thatis a formidable challenge, since the levels are inher-ently diVerent. A prominent problem is that elementsare not only nested within the sub-patterns or patternswhich they form, but also outnumber the latter. Theparadigmatic solution has been to make all of the ele-ments identical (but see Navon, 2003, for a study of theeVects of element heterogeneity). Despite the headstart that it grants to the local level (namely, multiplechances, as many as the elements, to be encoded), thatsolution has been regarded reasonable, judging by thepopularity of its usage.

A less consensual issue is the admissible range ofretinal positions that elements could occupy and stillmeet the demands of the paradigm. It has been sus-pected, as early as at the introduction of the paradigm(Navon, 1977, p. 368), that global advantage would beunderestimated if stimuli having one of their elementsat their center (or close to it) were presented at Wxa-tion. A possible reason is that in the local-directed con-dition the subject might do well to focus exclusively on

D. Navon (&)Department of Psychology, University of Haifa, Haifa 31905, Israele-mail: [email protected]

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the foveal element, which under that condition consti-tutes the imperative stimulus for any practical matter.That may render the rest of the compound stimulus nomore than irrelevant background, a quite unwelcomeconsequence considering that the issue is, after all, theeVects of globality within the compound stimulus whenprocessed as such (Navon, 2003).

Navon (1977) tried to solve the problem by present-ing stimuli with some spatial uncertainty, and observedconsiderable global advantage. In subsequent studiesthat did not employ spatial uncertainty, global advan-tage was observed only with small visual angles (e.g.,Grice et al., 1983; Kinchla & Wolfe, 1979; Lamb &Robertson, 1988).

Later, Navon (1981) advocated using stimuli inwhich the eccentricities of the global and local levelswere equated by virtue of having all elements on theenvelope of the compound stimulus (e.g., the letter C).Navon and Norman (1983) found that with such stim-uli, even when presented with spatial certainty, sub-stantial eVects of global advantage were obtainedalmost irrespective of visual angle. Further studies(Amirkhiabani & Lovegrove, 1996, 1999; Luna, 1993;Luna, Merino, & Marcos-Ruiz, 1990) basically con-Wrmed that. Still, most researchers studying global/localadvantage use stimuli having elements at the center.

In a study meant to directly compare, using the samesubjects, stimuli having elements only on, or close to,their envelopes with stimuli having elements at theircenters, the magnitude of global advantage was foundto be considerably smaller with the latter (Luna, 1993).

One question that comes to mind is how circum-scribed the impact of central elements is. Could it bethat it resides mostly in a single, most foveal, element?And how potent is that impact relative to the impact ofall other elements? The present study examines thatquestion by utilizing familiar stimuli that either have ordo not have just a dot at their centers, whereas all otherfeatures are located on their envelope.

Another question concerns the source of thedecrease in global advantage when central elementsare present. An obvious cause of that is the reductionin the global-to-local impact in the local-directed con-dition due to the ease of focusing just on the centralelement. Another possible cause may be that in theglobal-directed condition central elements that fall onthe fovea are perhaps more perceptible or salient thanelements closer to the stimulus envelope, due to sen-sory factors but possibly also to higher-level ones,hence give rise to greater local-to-global impact.

The study reported here was designed also to testthe latter hypothesis. Examining that calls for usingjust a global-directed task with a slight modiWcation in

the paradigm. In part of the trials not all elements wereresponse-associated (namely, compatible or incompati-ble with the global stimulus). In some trials only oneelement at a certain part of the global stimulus(denoted henceforth critical element) was response-associated, while all others were response-neutral(namely, neutral with respect to the global stimulus).In other trials the critical element was rather response-neutral, while all other elements were response-associ-ated. In the rest of the trials all the elements were iden-tical, as they typically are in compound letters used forprobing global/local advantage. This manipulation ofthe locus of response-associated elements can serve toexplore the impact of individual elements on theresponse to the global stimulus.

The impact of the critical element can be measured(a) by the eVect it has on responses to the global stimu-lus when it is the only response-associated element, (b)by the decrease in eVect from the condition in which allelements are the same to the condition in which onlythat speciWc element is made to be neutral. Those twomeasurements of the impact of the critical element canbe compared with similar measurements with respectto the impact of all other elements save the critical one.

To test the hypothesis in question, the centrality ofthe critical element within the global letter ought to bemanipulated. An eVect to the centrality of the elementon its impact, if found, might be due to either eccentric-ity per se or arise because feature processing is notevenly done at the center and at locations that are closeto the envelope irrespective of absolute retinal posi-tion. In this study I manipulated centrality betweensubjects in diVerent experiments.

On the other hand, it is possible that such an eVectwould be contingent on, or modulated by, elementdiagnosticity, namely the import of its presence to theidentiWcation of the global pattern. For example, thecentral element of a compound H is probably not asdiagnostic to identifying the H as the central elementof a compound X is to identifying the X (and thatshould be more pronounced to the extent that thereare fewer elements), since, whereas, the latter enablesthe detection of crossing and the quick detection offour angles, the former serves only to contribute to thecontinuity of a horizontal line segment. A critical ele-ment that is not suYciently diagnostic may not have animpact substantial enough to be measured. Hence, fortesting the hypothesis it seemed advisable to use criti-cal elements, for both centrality levels that were asdiagnostic as can be.

To obtain elements of maximal diagnosticity, pairsof Hebrew graphemes were used with forms that havevery little diVerence from each other. The graphemes

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Psychological Research (2008) 72:155–167 157

are the ones which are called, in Hebrew, Beth, Veth,Pe, Fe, each standing for a diVerent phonemes \b\, \v\,\p\, \f\, respectively). One of the distinctive featureswas made to comprise just one element. As can be seenin Fig. 1, which presents actual stimuli used inExperiments 1–3, the graphemes in each of the rowsdiVer only with respect to the most central element(marking a diacritical mark called, in Hebrew, dagesh,which in ordinary letters appears as a dot roughly atthe grapheme center). That element, denoted here dot,served as the critical element in Experiments 1 and 3.The graphemes in each of the columns of Fig. 1 ratherdiVer with respect to an element that falls on the enve-lope at the bottom right (plus another feature at theleft). The latter, denoted here tail, served as the criticalelement in Experiments 2 and 4. Clearly, the dot andtail diVer on their centrality within the global letter.

As noted, both dot and tail are highly diagnostic fordiscriminating between some graphemes. To examinewhether, or to what extent, their impacts on theresponse depend on that, the relevance of those dis-criminations was manipulated for the response calledfor. To manipulate that, the critical element could bemade to be either relevant or irrelevant for theresponse via the stimulus–response mapping called for

by the imperative task. When the choice is between allfour stimuli, both the dot and the tail are relevant.When the choice is between the stimuli at the left col-umn, the tail is relevant but the dot is not. When thechoice is between the stimuli at the upper row, the dotis relevant but the tail is not.

Experiment 1

This experiment was meant to study the impact of asingle central element on a global-oriented responsewhen it is highly diagnostic for the identiWcation calledfor by the imperative response discrimination.

Method

Subjects

Thirty-two students of the University of Haifa servedas subjects. All had normal or corrected-to-normalvision and participated in the experiment as part oftheir course credit.

Apparatus and setting

Presentation and data acquisition were controlled byan O2 SiliconGraphics computer. Visual stimuli werepresented on the computer display. Viewing distancewas about 100 cm. The room was fully illuminated. Thesubject sat in front of the display with the middle andindex Wngers of his\her both dominant and non-domi-nant hand placed on four keys of a computer keyboard.

Stimuli

Each of the stimuli was a global, large letter made upof local, smaller ones. A local letter measured 5 mm(0.29° of visual angle) vertically, and a global lettermeasured 53 mm (3.00° of visual angle) vertically.There were four possible global letters—Beth, Veth,Pe, Fe—that were made of four equivalent local letters(making up 16 combinations). The response-associa-tion of the local letters in the global letter’s dot orenvelope was manipulated by replacing the lettersthere with rectangles. The locus of response-associatedelements (all-elements, dot-only, all-but-dot) wasmanipulated only when the global letter was Beth orPe (the graphemes having a dot). To illustrate the locusmanipulation, three examples are presented in Fig. 2.Overall, there were thus 32 diVerent stimuli in theexperiment—16 in the all-elements locus, and 8 each inthe dot-only locus and in the all-but-dot locus.

Fig. 1 The four Hebrew graphemes used in Experiments 1–3.The illustrations here are just of 4 (out of 16) compound stimuliactually used—those having compatible elements throughout

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Design and procedure

Each trial began by a 10-ms warning beep and a pre-sentation of a 0.5-mm cross-shape Wxation mark at thecenter of the screen. One thousand milliseconds afterthe onset of the Wxation mark, a visual stimulus waspresented in the middle of the screen. Two thousandmilliseconds were allowed for making the response.Two hundred milliseconds after the subject made theresponse or after 2,000 ms have elapsed, the subse-quent trial started. Subjects were run individually in asingle session. The task was identiWcation of the globalletter.

The factors of the experiment were the global letter,the local letter and the locus. All the factors, except forresponse–key assignment, were manipulated withinsubjects and randomized within blocks. There were 512experimental trials in total. Those were presented infour equal blocks with a brief break separatingbetween each two consecutive blocks. A block with 32practice trials preceded the experimental blocks. Theresponse–key assignment variable was counterbal-anced between subjects. Both the middle Wnger andindex Wnger of a given hand were assigned to letterswith the same envelope (Beth and Veth, or Pe and Fe).That letter–pair identity was counterbalanced betweensubjects. The middle Wngers were always assigned to

letters with a dot (Beth or Pe), and the index Wngerswere assigned to letters without a dot (Veth or Fe).

Results

The data analyzed were mean latencies and percent-ages of incorrect responses.

Mean latencies were calculated for trials in whichthe responses were correct. In addition, trials withlatencies shorter than 250 ms or longer than 1,500 mswere excluded from analysis (3.8% of all correctresponses).

The major analyses were conducted on mean laten-cies for trials in which the global letters had a dot,namely Beth and Pe. Trials made up a factorial design,factors of which were compatibility and locus of theresponse-associated elements. The compatibility factorhad four levels, since global–local pairs could beincompatible just in the presence/absence of a dot (e.g.,Beth and Veth), just in envelope shape (e.g., Beth andPe), or in both (e.g., Beth and Fe). The locus factor hadthree levels—all-elements, dot-only, all-but-dot.Table 1 presents mean latencies and error percentagesas a function of the two compatibility factors and locus.

Since the issue in question concerns the interactionbetween locus and compatibility, and since this studydid not have neither hypotheses nor prior assumptionsabout the speciWc roles of dot and envelope in generat-ing the incompatibility eVect, the major analyses wereconducted to evaluate the eVect of the locus factor on ameasure of the compatibility eVect calculated by sub-tracting latency in the condition with full compatibility(both of dot and envelope) from the condition with nocompatibility at all (both of dot and envelope).Figure 3 presents mean compatibility eVect as a func-tion of locus. As can be seen, the compatibility eVect ismuch greater in the all-elements condition. One-wayanalysis for the factor compatibility yielded a signiWcant

Fig. 2 Three examples of stimuli in each of the three locus valuesin Experiments 1 and 3

Table 1 Mean latencies and error percentages in Experiment 1 as a function of envelope compatibility, dot compatibility and locus

Locus of response-associated elements

Envelope compatibility

Dot compatibility

Mean latency (ms)

Accuracy (error percentages)

All-elements Yes Yes 768 (99) 3.91No 800 (94) 5.37

No Yes 849 (98) 7.42No 883 (114) 7.23

Dot-only Yes Yes 816 (107) 6.84No 812 (102) 6.05

No Yes 834 (104) 6.44No 844 (112) 7.32

All-but-dot Yes Yes 786 (96) 4.20No 797 (101) 4.59

No Yes 844 (108) 4.49No 820 (98) 5.56

Standard deviations are shown in parentheses

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eVect, F(2,62) = 27.37, P < 0.0001, Mse = 2,755. A posthoc analysis showed a signiWcant diVerence betweenthe all-elements condition and the other two, but notbetween the dot-only condition and the all-but-dotcondition (F < 1).

Analysis on the arcsine square root transforms ofpercentages of incorrect responses yielded a non-sig-niWcant result, F(2,62) = 2.52, P < 0.09, Mse = 0.023. Nosign that the results in latency are due to speed–accu-racy tradeoV was indicated.

An additional, basically exploratory, analysis wasconducted to enable a breakdown of the source of thecompatibility eVect. Data were cast into a within-sub-ject three-way ANOVA, factors of which were enve-lope compatibility (viz, the match/mismatch in theenvelopes of the global letter and of the local one), dotcompatibility (viz, the match/mismatch of the globalletter and the local one in the presence/absence of adot) and locus. In the analysis of mean latencies signiW-cant main eVect was found for the factor locus,F(2,62) = 5.90, P < 0.01, Mse = 1,418, for the factorenvelope compatibility, F(1,31) = 112.3, P < 0.0001,Mse = 2,079, and for the factor dot compatibility,F(1,31) = 7.48, P < 0.01, Mse = 1,209. The interactions,locus £ dot compatibility and locus £ envelope com-patibility were found signiWcant, F(2,62) = 9.88,P < 0.001, Mse = 1,357, and F(2,62) = 16.71, P < 0.0001,Mse = 1,674. In addition, the triple interaction, enve-lope compatibility £ dot compatibility £ locus, wasalso found signiWcant, F(2,62) = 3.35, P < 0.05,Mse = 1,518.

Separate two-way analyses of dot compatibility£ envelope compatibility in every level of the locusfactor were conducted. The analysis in the all-elementscondition yielded signiWcant main eVects of envelopecompatibility, F(1,31) = 100.40, P < 0.0001, Mse = 2,154(82 ms), and of dot compatibility F(1,31) = 28.64,P < 0.0001, Mse = 1,197 (33 ms). No signiWcant interac-tion between these two factors was found (F < 1). The

analysis in the dot-only condition yielded a signiWcantmain eVect of envelope compatibility, F(1,31) = 10.81,P < 0.01, Mse = 1,837 (25 ms). The main eVect of dotcompatibility and of the interaction between the twocompatibility factors were not found signiWcant (F < 1for both). The analysis in the all-but-dot conditionyielded a signiWcant main eVect of envelope compati-bility, F(1,31) = 37.09, P < 0.0001, Mse = 1,436 (40 ms).The main eVect of dot compatibility was not found sig-niWcant (F < 1). The interaction between dot compati-bility and envelope compatibility was found signiWcant,F(1,31) = 6.95, P < 0.01, Mse = 1,440.

A three-way analysis of the arcsine square roottransforms of percentages of incorrect responsesyielded two main eVects for locus, F(2,62) = 6.70,P < 0.01, Mse = 0.0147, and envelope compatibility,F(1,31) = 7.88, P < 0.01, Mse = 0.0068. No other eVectwas found signiWcant, and again the pattern did notindicate any sign that the results in latency are due tospeed–accuracy tradeoV.

In order to assess the eVect of the dot in the globalletter, two-way analyses, with the factors presence/absence of global dot and compatibility (having twovalues—full compatibility vs. no compatibility) wereconducted only on data from trials in the all-elementscondition. In mean latency, the analysis yielded maineVects of global dot, F(1,31) = 33.37, P < 0.0001,Mse = 3208, and of compatibility, F(1, 31) = 66.33,Mse = 2,220. The interaction between these two vari-ables was found signiWcant as well, F(1,31) = 63.67,P < 0.0001, Mse = 1,115. Mean latency was shorter forglobal letters with dots (825 vs. 883 ms). More impor-tantly, the measure of the compatibility eVect wasfound much larger for those letters (115 vs. 21 ms;though the latter is also signiWcant, P < 0.05), corrobo-rating the hypothesis that the main source of the eVectis located at the dot.

In accuracy, the analysis yielded a signiWcant maineVect of global dot, F(1,31) = 18.63, P < 0.001,Mse = 0.0132, but not for compatibility, F(1,31) = 3.71,P < 0.07, Mse = 0.008. The interaction between thesetwo variables was found signiWcant, F(1,31) = 13.53,P < 0.001, Mse = 0.009. The pattern of accuracy resultswas quite compatible with the pattern of latency ones.

In summary, two main conclusions emerge fromthe data: one, a single response-associated elementat the dot is enough to produce a signiWcant compati-bility eVect; two, eliminating just the dot elementfrom the set of response-associated elements (bymaking it neutral) reduces the compatibility eVectconsiderably, apparently enough to make it indistin-guishable from the eVect of the single, foveal ele-ment.

Fig. 3 Mean compatibility eVect (in ms) as a function of locus inExperiment 1

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Experiment 2

This experiment was meant to study the impact of asingle non-central element on a global-orientedresponse under high response diagnosticity.

Accordingly, the method was the same as inExperiment 1, except that the locus of response-associ-ated elements was manipulated only when the globalletter was Beth or Veth (the graphemes having a tail).To illustrate the locus manipulation in this experiment,three examples are presented in Fig. 4. Thirty-two stu-dents of the University of Haifa served as subjects,none of them served as a subject in Experiment 1. Allhad normal or corrected-to-normal vision and partici-pated in the experiment as part of their course credit.

Results

The analyses were conducted on mean latencies anderror percentages for trials where the global letters hada tail, named Beth and Veth. Table 2 presents meanlatencies and error percentages as a function of the twocompatibility factors and locus. The locus factor hadthree levels—all-elements, tail-only and all-but-tail.

The major analyses were conducted in order to eval-uate the eVect of the locus factor on the compatibilityeVect calculated by subtracting mean latency in the

condition with full compatibility from mean latency inthe condition with no compatibility at all. Figure 5 pre-sents mean compatibility eVect as a function of locus.One-way analysis for the factor compatibility yielded asigniWcant eVect, F(2,62) = 43.65, P < 0.0001,Mse = 2,084. A post hoc analysis showed a signiWcantdiVerence between the tail-only condition and othertwo conditions, but not between the all-elements andthe all-but-tail conditions (F < 1). Note that the simpleeVect in the tail-only condition is paradoxical, sincelatency is longer in trials with compatibility than in tri-als with incompatibility.

Analysis on the arcsine square root transforms ofpercentages of incorrect responses yielded a signiWcanteVect, F(2,62) = 4.67, P < 0.01, Mse = 0.0192. A posthoc analysis showed a signiWcant diVerence betweenthe tail-only condition and other two conditions, butnot between the all-elements and the all-but-tail condi-tions (F < 1). Note that the simple eVect in the tail-onlycondition is paradoxical just like in the latency analysis,so no sign that the results in latency are due to speed–accuracy tradeoV was indicated.

To enable a further breakdown of the source of thecompatibility eVect, data were cast into a within-sub-ject three-way ANOVA, factors of which were enve-lope compatibility, tail compatibility and locus. In theanalysis of mean latencies signiWcant main eVects werefound for the factor locus, F(2,62) = 115.17, P < 0.0001,Mse = 933, and for the factor envelope compatibility,F(1,31) = 64.41, P < 0.0001, Mse = 1,745. The factor dotcompatibility was not found signiWcant (F < 1). Theinteractions locus £ dot compatibility and locus £envelope compatibility were found signiWcant, F(2,62)= 4.27, P < 0.05, Mse = 968, and F(2,62) = 73.94,P < 0.0001, Mse = 1,309. In addition, the triple interac-tion envelope compatibility £ dot compatibility£ locus was also found signiWcant F(2,62) = 3.77,P < 0.05, Mse = 1,471.

Fig. 4 Three examples of stimuli in each of the three locus values in Experiment 2




Dot compatibility

Mean latency(ms)



No Yes 818 (106) 5.37No 815 (107) 4.98

Tail-only Yes Yes 752 (94) 3.81No 737 (98) 3.03

No Yes 704 (97) 2.44No 727 (89) 3.22

All-but-tail Yes Yes 742 (97) 2.44No 761 (94) 4.88

No Yes 807 (106) 5.66No 813 (101) 4.59


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Separate two-way analyses of dot compatibility £envelope compatibility in every level of the locus factorwere conducted. The analysis in the all-elements condi-tion yielded a signiWcant main eVect of envelope com-patibility, F(1,31) = 91.89, P < 0.0001, Mse = 1,851(73 ms). The main eVect of dot compatibility and theinteraction between dot compatibility and envelopecompatibility were not found signiWcant, F(1,31) =2.17, P < 0.15, Mse = 1,477, and F(1,31) = 1.36,Mse = 1,080. The analysis in the tail-only conditionyielded a signiWcant main eVect of envelope compati-bility, F(1,31) = 26.97, P < 0.01, Mse = 980 (¡29 ms).The main eVect of dot compatibility was not found sig-niWcant (F < 1). The interaction between the two com-patibility factors was found signiWcant F(1,31) = 6.13,P < 0.05, Mse = 1,931. The analysis in the all-but-tailcondition yielded a signiWcant main eVect of envelopecompatibility, F(1,31) = 71.45, P < 0.0001, Mse = 1532(58 ms). The main eVect of dot compatibility was notfound signiWcant, F(1,31) = 3.94, P < 0.06, Mse = 1,281.The interaction between dot compatibility and enve-lope compatibility was not found signiWcant either,F(1,31) = 1.49, P < 0.23, Mse = 1,080.

A three-way analysis of the arcsine square roottransforms of percentages of incorrect responsesyielded two main eVects: for locus, F(2,62) = 3.22,P < 0.05, Mse = 0.01, and for envelope compatibility,F(1,31) = 7.52, P < 0.01, Mse = 0.0095. The interactionbetween locus and envelope compatibility was foundsigniWcant as well, F(2,62) = 7.71, P < 0.001,Mse = 0.0106. The triple interaction envelopecompatibility £ tail compatibility £ locus was alsofound signiWcant F(2,62) = 3.78, P < 0.05, Mse = 0.0097.No other eVect was found signiWcant, and again thepattern did not indicate any sign that the results inlatency are due to speed–accuracy tradeoV.

Like in Experiment 1, the eVect of the dot in the glo-bal letter was assessed by two-way analyses, the pres-

ence/absence of global dot and compatibility (havingtwo values—full compatibility vs. no compatibility)applied only on data from trials in the all-elements con-dition. In mean latency, the analysis yielded a maineVect of compatibility, F(1, 31) = 59.13, Mse = 2,103,but not of global dot (F < 1). The interaction betweenthese two factors was found signiWcant, F(1,31) = 24.11,P < 0.0001, Mse = 1,422. Like in Experiment 1, themeasure of the compatibility eVect was found larger forglobal letters with dots (95 vs. 30 ms; though the latteris also signiWcant, P < 0.01).

The analysis of accuracy data yielded a signiWcantmain eVect of compatibility, F(1,31) = 8.14, P < 0.01,Mse = 0.0132. The eVect of global dot and that of theinteraction between global dot and compatibility was notfound signiWcant (F < 1). No sign that the results inlatency are due to speed–accuracy tradeoV was indicated.

In summary, a compatibility eVect was found in thisexperiment as well. However, it is not present with asingle response-associated element at the tail, andeliminating just the tail element from the set ofresponse-associated elements does not seem to reducethe compatibility eVect.

The paradoxical eVect of compatibility in the tail-only condition (that seems to be more pronounced indot-consistent trials), namely that latency is longer intrials with compatibility than in trials with incompati-bility, is hard to explain. A post hoc interpretation thatseems most plausible is that somehow, when most ele-ments are neutral, a tail made of a Beth is not easilygrouped with the other elements. That does not aVectresponse selection that, in tail-only trials, is to be basedjust on the presence of a global dot, but it perhapsimpedes the binary discrimination of envelope-shape(Beth/Veth vs. Pe/Fe) that determines the selection ofresponding hand. Anyhow, the very fact that this eVectis paradoxical suggests that it does not arise from theidentiWcation of the tail element itself, hence is hardlypertinent for studying the source of local-to-globaleVects, which is the objective of the present study.

To compare Experiment 2 with Experiment 1, anANOVA was conducted on the measure of the com-patibility eVect (calculated by subtracting latency in thecondition with full compatibility from the conditionwith no compatibility at all) in both (in trials for whichlocus could be manipulated). The factors were experi-ment and locus.

SigniWcant main eVects were found for the factorexperiment, F(1,62) = 7.38, P < 0.01, Mse = 3,365 andfor the factor locus, F(2,124) = 51.25, P < 0.0001,Mse = 2,420. The interaction between the two factorswas found signiWcant as well, F(2,124) = 17.51,P < 0.0001, Mse = 2,420.

Fig. 5 Mean compatibility eVect (in ms) as a function of locus in Experiment 2

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As can be readily seen by re-inspecting Figs. 3 and 5,the compatibility eVect in all-elements trials inExperiment 2 is smaller than the respective eVect inExperiment 1. At least part of that Wnding must be dueto the fact that in Experiment 2 the compatibility mea-sure is somewhat diluted by trials in which there was nodot at all (50% of those analyzed above).

More importantly, whereas, the response to a globalletter with a diagnostic central element is aVected bythat element in itself about as much as it is aVected byall other elements taken together (see Fig. 3), theresponse to a global letter with a diagnostic element atthe envelope is not aVected by it in itself more than byany other element in itself (see Fig. 5).

That entails that the local-to-global eVect isexpected to be larger in global letters having elementsat the center. Indeed, even in this study, in which lesstrials had global letters having elements at their cen-ters, the compatibility eVect in all-elements trials wasquite larger in letters having a dot than in letters thatlacked a dot.

A separate two-way ANOVA (factors of whichwere experiment and global dot) on the compatibilitymeasure in all-elements trials in both experiments wasconducted. A signiWcant main eVect was found only forthe factor global dot, F(1,62) = 80.40, P < 0.0001,Mse = 2,538. The main eVect of experiment was notsigniWcant (F < 1). The interaction between experimentand global dot was found signiWcant, F(1,62) = 2.61,P < 0.0001, Mse = 0.12. Thus, although as reportedabove the eVect of global dot was highly signiWcant(P < .001) in Experiment 2, it was smaller (and appar-ently restricted to the letters Beth and Veth). A plausi-ble account is that in contrast with Experiment 1, trialsin Experiment 2 that had letters having just oneresponse-associated element had it on the envelope(speciWcally, the tail), which might have biased thespread of visual attention towards the envelope.

Experiment 3

This experiment was meant to study the eVect of a sin-gle central element on a global-oriented response whenit is not response-diagnostic. Accordingly, the methodwas the same as in Experiment 1, except that there wereonly two global letters, Beth and Pe, both having a dot,and only two corresponding local letters, Beth and Pe(making up four combinations). Consequently,response choice was binary, with the index Wngers ofboth hands responding to the two stimuli. The locus fac-tor was manipulated as it was in Experiment 1. Overall,there were 12 diVerent types of stimulus in the experi-

ment—4 in each level of the locus factor. There were504 experimental trials in total (42 trials for each stimu-lus type). These were presented in four equal blockswith a brief break separating between each two consec-utive blocks. A practice block consisting of 32 practicetrials preceded the experimental blocks. Subjects usedthe middle Wngers of both hand to respond. Theresponse–key assignment variable was counterbalancedbetween subjects. Sixteen students of the University ofHaifa served as subjects, none of them served as a sub-ject in either Experiment 1 or Experiment 2. All hadnormal or corrected-to-normal vision and participatedin the experiment as part of their course credit.

Results

Table 3 presents mean latencies and error percentagesas a function of compatibility and locus. Mean latencydata were cast into a within-subject two-way ANOVA,factors of which were compatibility and locus ofresponse-associated elements. The compatibility factorhad two levels. The locus factor had three levels—all-elements, dot-only and all-but-dot.

A signiWcant main eVect was found only for the fac-tor compatibility, F(1,15) = 16.37, P < 0.001, Mse = 689(22 ms). The main eVect of locus was not found signiW-cant, F(2,30) = 2.86, P < 0.08, Mse = 421; neither wasthe interaction between locus and compatibility,F(2,30) = 2.37, P < 0.11, Mse = 328.

The overall error rate was small (3.03%). Analysisof the arcsine square root transforms of percentages ofincorrect responses yielded no signiWcant main eVects,F < 1 for locus and F(1,15) = 1.16, P < 0.30,Mse = 0.0045 for compatibility. The interactionbetween locus and compatibility was also not foundsigniWcant, F(2,30) = 1.20, P < 0.31, Mse = 0.0034. Nosign that the results in latency are due to speed–accu-racy tradeoV was indicated.

Thus, when the dot has no response diagnosticity,the compatibility eVect is still signiWcant. The eVect is

Table 3 Mean latencies and error percentages in Experiment 3as a function of compatibility and locus



Compatibility Mean latency(ms)


All-elements Yes 582 (64) 2.90No 616 (74) 4.01

Dot-only Yes 579 (65) 2.68No 596 (76) 3.05

All-but-dot Yes 582 (66) 2.83No 598 (67) 2.68

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much smaller than that in Experiment 1, where the dotis response diagnostic to some extent. That may be dueto the fact that binary choice is easier, hence less sensi-tive to the impact of the elements. Another possiblecause may be the exclusion of local letters that lack adot, hence the impact of dot incompatibility present inExperiment 1. The absence of interaction betweencompatibility and locus is yet another demonstration ofthe potency of the impact of the single dot element onthe global response. This is especially interesting, sincein this experiment the dot had no response diagnostic-ity whatsoever.

Experiment 4

One may worry that in Experiments 1–3 the centralitymanipulation is not quite independent of feature diag-nosticity. While the presence/absence of the dot fullydetermines one aspect of response-associated stimulusidentity—the distinction between the graphemes in theWrst and second columns of Fig. 1b, the presence/absenceof the tail is less diagnostic. The distinction between thegraphemes in the Wrst and second rows of Fig. 1b can bedone not only by the presence/absence of the tail of theBeth and Veth but also by the presence/absence of thehook-like feature at the left of the Pe and Fe.

Accordingly, another experiment was devised,which is actually a variant of Experiment 2 and in thatthe tail was made to be as diagnostic as the dot byreplacing the Pe–Fe pair of graphemes with anotherpair of graphemes distinguished by a central diacriticalmark, namely what here is referred to as dot (Kaphand Khaph) that diVers from the Beth–Veth pair onlyby the presence/absence of a tail (see Fig. 6). Thus, thefour possible global letters were Beth, Kaph, Veth andKhaph, and so were the four possible local ones. Thelocus factor was manipulated only for the global lettersBeth and Veth.

Since this experiment was meant just as a control forthe possibility that the choice of stimulus letters couldsubstantially interact with the pattern of results, fewersubjects were used in it. Sixteen students of the Univer-sity of Haifa served as subjects, none of them served asa subject in Experiment 1, Experiment 2, orExperiment 3. All had normal or corrected-to-normalvision and participated in the experiment as part oftheir course credit.

Results

The analyses were conducted on mean latencies anderror percentages for trials where the global letters had

a tail, named Beth and Veth. Table 4 presents meanlatencies and error percentages as a function of the twocompatibility factors and locus. The locus factor hadthree levels—all-elements, tail-only and all-but-tail.

The major analyses were conducted in order to eval-uate the eVect of the locus factor on the compatibilityeVect calculated by subtracting mean latency in thecondition with full compatibility from mean latency inthe condition with no compatibility at all. Figure 7 pre-sents mean compatibility eVect as a function of locus.One-way analysis for the factor compatibility yielded asigniWcant eVect, F(2,30) = 9.81, P < 0.001, Mse = 2,476.A post hoc analysis showed a signiWcant diVerencebetween the tail-only condition and the other two con-ditions, but not between the all-elements and the all-but-tail conditions (F < 1).

Analysis of the arcsine square root transforms ofpercentages of incorrect responses yielded a signiWcanteVect, F(2,30) = 8.21, P < 0.001, Mse = 0.0156. A posthoc analysis showed a signiWcant diVerence betweenthe tail-only condition and other two conditions, butnot between the all-elements and the all-but-tail condi-tions (F < 1). Just as in Experiment 2, the simple eVect

Fig. 6 The four Hebrew graphemes used in Experiment 4. Theillustrations here are just of four (out of 16) compound stimuliactually used—those having compatible elements throughout(note the diVerence between them and the stimuli illustrated inFig. 1)

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in the tail-only condition is paradoxical, like in thelatency analysis, so no sign that the results in latencyare due to speed–accuracy tradeoV was indicated.

To enable a further breakdown of the source of thecompatibility eVect, data were cast into a within-sub-ject three-way ANOVA, factors of which were enve-lope compatibility, dot compatibility and locus. In theanalysis of mean latencies, signiWcant main eVects werefound for the factor locus, F(2,30) = 18.25, P < 0.0001,Mse = 1,876, and for the factor envelope compatibility,F(1,15) = 8.19, P < 0.05, Mse = 2,499. The factor dotcompatibility was not found signiWcant, F(1,15) = 2.58,P < 0.12, Mse = 826. The interaction locus £ envelopecompatibility was found signiWcant, F(2,30) = 10.87,P < 0.001, Mse = 1,535. In addition, the triple interac-tion envelope compatibility £ dot compatibility £locus was also found signiWcant F(2,30) = 6.69,P < 0.01, Mse = 2,075.

Separate two-way analyses of dot compatibility£ envelope compatibility in every level of the locusfactor were conducted. The analysis in the all-elementscondition yielded a signiWcant main eVect of envelopecompatibility, F(1,15) = 24.69, P < 0.001, Mse = 14,751(47 ms). The main eVect of dot compatibility and the

interaction between dot compatibility and envelopecompatibility were not found signiWcant, F < 1 andF(1,15) = 2.01, P < 0.18, Mse = 2,900, respectively. Theanalysis in the tail-only condition yielded non-signiW-cant main eVects of envelope compatibility and of dotcompatibility, F(1,15) = 1.68, P < 0.22, Mse = 2,168 andF < 1, respectively. On the other hand, the interactionbetween dot compatibility and envelope compatibilitywas found signiWcant, F(1,15) = 6.43, P < 0.05,Mse = 2,404. The analysis in the all-but-tail conditionyielded signiWcant main eVects of both envelope com-patibility, F(1,15) = 7.15, P < 0.05, Mse = 1,925 (29 ms)and dot compatibility, F(1,15) = 5.22, P < 0.05,Mse = 1,082 (18 ms). The interaction between dot com-patibility and envelope compatibility was found signiW-cant as well, F(1,15) = 8.67, P < 0.01, Mse = 794.

A three-way analysis of the arcsine square roottransforms of percentages of incorrect responsesyielded a signiWcant main eVects for locus,F(2,30) = 3.90, P < 0.05, Mse = 0.015. The main eVectsof envelope compatibility and of dot compatibilitywere not found signiWcant (F < 1 for both). The inter-action between locus and envelope compatibility wasfound signiWcant, F(2,30) = 5.22, P < 0.05,Mse = 0.0074. The interaction between dot compatibil-ity and locus was found signiWcant as well,F(2,30) = 4.01, P < 0.05, Mse = 0.104. The triple inter-action envelope compatibility £ tail compatibility£ locus was also found signiWcant F(2,62) = 5.27,P < 0.05, Mse = 0.014. No other eVect was found sig-niWcant, and again the pattern did not indicate any signthat the results in latency are due to speed–accuracytradeoV.

Like in Experiments 1 and 2, the eVect of the dot inthe global letter was assessed by two-way analyses(presence of global dot and compatibility) applied onlyon data from trials in the all-elements condition. Inmean latency, the analysis yielded a main eVect of com-




Dot compatibility

Mean latency (ms)



No Yes 868 (140) 5.66No 852 (137) 4.69

Tail-only Yes Yes 818 (111) 4.69No 784 (112) 4.69

No Yes 771 (124) 4.10No 800 (127) 1.95

All-but-tail Yes Yes 795 (98) 6.05No 834 (111) 4.30

No Yes 845 (119) 5.27No 843 (123) 8.98


Fig. 7 Mean compatibility eVect (in ms) as a function of locus inExperiment 4

48

-18

51

-40

-30

-20

-10

0

10

20

30

40

50

60

All-but-tail Tail-only All- elements


Co

mp

atib

ility

(in

mse

c)

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patibility, F(3, 45) = 17.07, P < 0.0001, Mse = 1,730.The main eVect of global dot was only close to signiW-cance, F(1,15) = 4.10, P < 0.06, Mse = 972, and theinteraction between these two factors was not foundsigniWcant, F(3,45) = 1.37, P < 0.26, Mse = 1,542. Thepattern, however, was in the same direction as inExperiments 1 and 2. The measure of the compatibilityeVect was found larger for global letters with dots,though the diVerence was smaller (74 vs. 50 ms) andonly approached signiWcance, F(1,15) = 2.67, P = 0.12,Mse = 882. The analysis of accuracy data yielded a sig-niWcant main eVect of compatibility, F(3,45) = 4.33,P < 0.01, Mse = 0.012. The eVect of global dot and thatof the interaction between global dot was not foundsigniWcant (F < 1), but the pair-wise interaction wasfound signiWcant, F(3,45) = 2.82, P < 0.05, Mse = 0.01.No sign that the results in latency are due to speed–accuracy tradeoV was observed.

Thus, overall the results are fairly similar to those ofExperiment 2. That renders it gratuitous to addressthem separately. On the whole, they aVord some cross-validation for the conclusion drawn from the compari-son between Experiments 1 and 2 on the role of cen-trality of elements. Though the critical element inExperiment 2 may not be equated enough on featurediagnosticity to the critical element in Experiment 1,the critical element in Experiment 4 is quite equated tothe latter, and yet it did not contribute to the local-to-global eVect, just as it did not in Experiment 2.

General discussion

The objective of comparing the impacts of an individ-ual central element and an individual non-central ele-ment matched for diagnosticity has been met. Theresults indicate that there is a substantive diVerence,qualitative in this instance.

The results of Experiment 1 demonstrate how cru-cial for a local-to-global eVect can be the identity of acentral element at an isolated location (referred tohere as “dot”) that is response diagnostic. The eVect ofthe compatibility of element identity with the globalresponse on mean latency is reduced as much as by70% as a result of just making that element neutral(see Fig. 3). That residual eVect, due to the combinedimpacts of 18–20 elements, is not signiWcantly largerthan the eVect of a single response-associated elementat the center (where all others are neutral). Attributingthat to mere element heterogeneity does not seemplausible, since even more pronounced degrees of ele-ment heterogeneity have been demonstrated to barelyinXuence local-to-global eVects (Miller, 1981; Navon,

2003). Furthermore, in trials in which that elementdoes not appear at all (namely, when the global letter isVeth or Fe), the local-to-global eVect is relatively mea-ger (21 ms).

The special impact of the central element is evi-denced even more convincingly in Experiment 3. Sincethe central element is rendered response-irrelevant inthat experiment, so that the response is determinedsolely by envelope features (tail, for one), one mightexpect the impact of elements on the envelope toincrease relative to the central one. Nonetheless, theeVect of the central element is still about the same asthe eVect of all other elements taken together (seeFig. 3). In that case all the eVects, including the oneobtained with perfectly homogenous local level, areconsiderably milder than the corresponding ones inExperiment 1. Part of it might be due to the fact that,by the task deWnition, compatibility here is aVectedonly by envelope compatibility. However, the magni-tude of eVect reduction suggests that it must be duealso to some other factor. Presumably, the local-to-glo-bal eVect is quite sensitive to, though not totally depen-dent on, the ampliWcation of attention to the centralelement called for by its being response relevant, as itis in Experiment 1. When the latter is irrelevant, notonly it but all other elements as well seem to attract lit-tle attention.

The particularly important role of centrality is dem-onstrated by the absence, in Experiment 2, of a similarcontribution to the local-to-local eVect of the identityof a response-diagnostic element that is located on theletter envelope (at a location referred to here as“tail”). The eVect of compatibility on mean latency isnot reduced at all by making that element neutral (seeFig. 5). Also, a single response-associated element atthe tail (where all others are neutral) does not contrib-ute at all to the local-to-global eVect. Actually, it pro-duces a modest paradoxical eVect, probably due topoor grouping in some stimuli. The same was found inExperiment 4, where the feature diagnosticity of thetail was higher. Thus, a non-central element does notmatter for the extent of the local-to-global eVect evenwhen it is maximally diagnostic, as diagnostic as the dotis.

One might contend that the tail is not as salient asthe dot is, because it is grouped with the rest of the let-ter envelope, unlike the dot that stands alone. Ofcourse, using naturalistic stimuli entails as a cost someimperfection in experimental control. However, thecost cannot be critical here, since a salience disparitywould have probably resulted in a mere quantitativediVerence, yet the diVerence observed here betweenthe impacts of dot and tail was that the former is pres-

123


ent while the latter is absent. Furthermore, whilesalience might have played a part in the impact of a sin-gle response-associated element at the dot or at thetail, it is hard to see why it would aVect much thereduction of the eVect due to elimination of a singleresponse-associated element at the dot or at the tail.Finally, even if salience had a part, it could not possiblyhave accounted for the whole magnitude of the eVectdemonstrated here, since centrality was found to haveeVects even with central elements that were groupedwith the other ones (Luna, 1993).

It seems, thus, that local-to-global eVects are partic-ularly due to central elements, especially when thoseare diagnostic for the global response. Non-central ele-ments make much smaller impacts, possibly negligible,even when they are highly diagnostic. It seems plausi-ble that by the time the global response is selected (orat least is already immune to any eVect exerted by ele-ments) the identity of most elements is not yet madeexplicit. In the horse race between them, central ele-ments have a much higher chance to win, so they havea very good chance to aVect the global response. Onthe other hand, since there are quite a few non-centralcontestants, there is also a decent likelihood that atleast one of them would win the race (despite the min-ute likelihood for any particular one of them, e.g., thetail element, to win it). Probably, this is the reason whythe compatibility eVect in all-elements trials was con-siderably larger than in dot-only ones.

What does this imply about testing perceptual pre-cedence or post-perceptual primacy? The pronouncedeVect of element location within the global pattern isanother reminder that we should be less dogmaticabout “processing the local level”. In naturalistic stim-uli, in which the local level comprises of diverse fea-tures and elements, processing it must take more timethan it takes in a homogenous compound stimulus toprocess the winner in the horse race of elements. Since,as shown here, even one central element may beenough to produce a considerable local-to-global eVectwith compound stimuli, it seems dubious to regard thatas a safe measure of the temporal locus of local pro-cessing in the course of perceptual processing. By anal-ogy, if nose shape was somehow found earlier toregister or evaluate than overall face conWgurationwas, it would hardly be evidence that the perception ofall facial features preceded the perception of face con-Wguration.

The least that can be done to amend that in the com-pound stimuli paradigm is to equate eccentricities ofthe global and local levels, as proposed by Navon andNorman (1983) and followed afterwards in a number ofstudies (e.g., Amirkhiabani & Lovegrove, 1996, 1999;

Blanca, Luna, Lopez-Montiel, Zalabardo, & Rando,2002; Luna, 1993; Miller & Navon, 2002; Navon, 1991,2003). That is not much better as a measure of thattemporal locus, since unlike in compound stimuli, thediversity of the contents of the local level in naturalisticstimuli is quite higher, but it may serve as a reasonablemeasure of the earlier time in the course of processingat which local processing could take place, given thatthe comparison is adequately controlled.

It, thus, seems plausible to conclude that the studiesof global/local advantage using stimuli with central ele-ments dubiously illuminate the issue of perceptual pre-cedence. Stimuli lacking such elements fair better.True, many naturalistic stimuli have features at theircenters. That must worry whoever regards the issue interms of prevalence (namely, is it the case that in themajority of real-world patterns global constituentshave some advantage over local constituents?). How-ever, from the point of view of whoever is interested inglobal/local precedence as a disposition issue (namely,is it the case that the perceptual system is inherentlydisposed to favor global constituents?), this would beseen to be a useful means for attaining a better con-trolled testing Weld (cf Navon, 2003, p 278–280, for adiscussion of this distinction about foci of interest).The practical lesson for experimenters from the lattercamp is that stimuli such as the letters C or O are to bepreferred over stimuli such as the letters H or S.

Acknowledgments The experiments reported in this paperwere supported in part by a grant no 883/03 from the Israeli Sci-ence Foundation. The author is indebted to Ziziana Lazar forprogramming the experiments, to Ori Amir, Jonathan Dvash andNoa shalev for running them and to Ronen Kasten for helping insetting them up and conducting the analyses.

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