Hemispheric asymmetries for global and local processing as a function of stimulus exposure duration

Hemispheric asymmetries for global andlocal processing as a function of

stimulus exposure duration

Denise L. Evert* and Meghan Kmen

Psychology, Skidmore College, Saratoga Springs, NY 12866, USA

Accepted 13 August 2002

Abstract

The experiments assess the relationship between stimulus exposure duration and hemi-

spheric asymmetries for global and local processing. Six durations (27, 40, 53, 67, 80, and

147ms) were tested in a selective attention task in which hierarchical letterforms were pre-

sented unilaterally to the left or right visual field. The results indicated that left hemisphere-

local asymmetries were demonstrated more often than right hemisphere-global asymmetries

and that asymmetries were most commonly found in the middle range of durations tested. The

pattern of results emphasizes the importance of further study into those conditions under

which the predicted asymmetries can be reliably demonstrated in healthy individuals.

� 2003 Elsevier Science (USA). All rights reserved.

Keywords: Global and local processing; Levels of processing; Hemispheric asymmetries; Hemispheric

specialization; Task demands; Exposure duration; Selective attention

1. Introduction

The limited processing capacity of the brain makes it impossible to process all of

the information impinging upon our senses at any one point in time with equal ef-

ficiency. Thus, some mechanism that allows us to direct our attention is required.This mechanism is selective attention, directing our focus to those aspects of the

environment that are most relevant to our current goal-directed behavior. Visual

selective attention can be directed to a particular region of space in preparation for

the processing of information to be presented at that location (spatially based at-

tention). Pre-cueing paradigms have widely been used to manipulate the direction of

such visual selective attention (e.g., Evert & Oscar-Berman, 2001; Posner, 1980;

Posner & Petersen, 1990; Verfaellie, Bowers, & Heilman, 1988). Visual selective at-

tention also can be directed to specific objects, or levels of objects, within a region ofspace (object-based attention). For example, attention can be directed toward a more

global level (e.g., attending to the overall configurations made by a marching band

during a halftime show), or toward a more local level (e.g., attending to one of the

Brain and Cognition 51 (2003) 115–142

www.elsevier.com/locate/b&c

*Corresponding author. Fax: 1-518-580-5319.

E-mail address: [email protected] (D.L. Evert).

0278-2626/03/$ - see front matter � 2003 Elsevier Science (USA). All rights reserved.

doi:10.1016/S0278-2626(02)00528-6

mail to: [email protected]

trumpet players in the marching band who just tripped and fell). Global and local

levels of processing are not, however, absolute. In the example above, attention to

the fallen trumpet player could also represent global processing while attention to

the redness of his/her face could represent local processing. Thus, global and local

levels are relative, not absolute. Hierarchical figures consisting of larger letters or

shapes composed of smaller letters or shapes (e.g., the letter H comprised of smaller

I�s) often are used to assess global and local processing (e.g., Navon, 1977).

Investigations of global and local levels of processing point to three intriguingphenomena: global precedence, inter-level interference effects, and hemispheric

asymmetries for global and local processing. Global precedence refers to the finding

that global information is generally processed more efficiently than detailed local

information (Navon, 1977).1 This precedence is inferred from findings of faster and/

or more accurate responding when attention is directed to the global level of a

stimulus relative to when attention is directed to the local level of the stimulus (e.g.,

Luna, 1993; Navon, 1977). Inter-level interference effects can be observed when the

global and local stimuli of a hierarchical figure differ from each other; often times,the interference effects are asymmetric (e.g., Boles & Karner, 1996; Martin, 1979;

Navon, 1977). For example, an inconsistent global distractor (e.g., the letter H) may

interfere with the processing of the local elements of that figure (e.g., I�s), whereas aninconsistent local distractor will provide little, if any, interference on the processing

of the global figure. Thus, even when participants are asked to attend exclusively to

the local elements, an inconsistent global distractor can interfere with the efficiency

of processing (e.g., identification) of the local form. Although asymmetric interfer-

ence effects support the phenomenon of global precedence, inter-level interference,and global precedence are dissociable (Lamb & Yund, 1996).

Of particular interest to the studies reported here is the third phenomenon,

namely the evidence suggesting that the hemispheres of the brain differ in the effi-

ciency with which they process global and local information. More specifically, the

right hemisphere (RH) appears to be more specialized for global processing and the

left hemisphere (LH) appears to be more specialized for local processing. There is

converging evidence for these hemispheric asymmetries from studies with brain

damaged individuals (Delis, Robertson, & Efron, 1986; Doyon & Milner, 1991;Lamb, Robertson, & Knight, 1990; Rafal & Robertson, 1995; Robertson, Lamb, &

Knight, 1988), functional brain imaging studies (Fink et al., 1996, 1997b, Fink,

Marshall, Halligan, & Dolan, 1999; Martinez et al., 1997; but see Fink et al., 1997b),

event-related potential (ERP) studies (Heinze, Hinrichs, Scholz, Burchert, & Man-

gun, 1998; but see Johannes, Wieringa, Matzke, & Munte, 1996), behavioral studies

with animals (Fagot & Deruelle, 1997; Hopkins, 1997), and behavioral studies with

healthy humans (Banich & Noll, 1993; Blanca, Zalabardo, Gar�ıı-Criado, & Siles,

1994; Hellige, Corwin, & Jonsson, 1984; H€uubner, 1997, 1998; Kimchi & Merhav,1991; Martin, 1979; Martinez et al., 1997; Robertson, Lamb, & Zaidel, 1993; Ser-

gent, 1982; Van Kleeck, 1989 [meta-analysis], Versace & Tiberghien, 1988; Yovel,

Yovel, & Levy, 2001). However, while many behavioral studies with healthy indi-

viduals have found evidence to support the predicted asymmetries, findings from

other studies with healthy individuals have not supported such a dichotomy (Ali-

visatos & Wilding, 1982; Blanca Mena, 1992; Boles, 1984; Boles & Karner, 1996;

Lamb & Robertson, 1988; Polich & Aguilar, 1990; Van Kleeck, 1989 [non meta-

analysis]).

1 Although Navon (1977) originally argued that global and local information are processed sequentially,

with the global level being processed first, others have demonstrated that information from the global and

local levels can be processed in parallel (e.g., Hoffman, 1980; H€uubner, 1997; Kinchla, Solis-Macias, &

Hoffman, 1983; Miller, 1981). Thus, global precedence is here referred to as more efficient processing of

global information without making specific claims about the time course of such processing.

116 D.L. Evert, M. Kmen / Brain and Cognition 51 (2003) 115–142

The inconsistency in demonstrating hemispheric asymmetries for global and local

processing in behavioral studies with healthy humans was of most interest here. One

explanation given for the inconsistent results among healthy humans is that the

expression of hemispheric specialization for global and local processing may be

dependent upon the relative visibility of the stimuli in the experiment (Blanca et al.,

1994). This hypothesis suggests that as task demands are increased and stimulus

visibility decreases, there is a greater likelihood of demonstrating hemispheric

asymmetries. Although there are a multitude of ways in which stimulus visibility canbe manipulated in a particular study (e.g., eccentricity, size, and spatial frequency

content), this discussion focuses on the manipulation of the exposure duration of the

stimuli. Two studies have directly addressed the relationship between stimulus ex-

posure duration and hemispheric asymmetries for global and local processing

(Blanca et al., 1994; Boles & Karner, 1996).

In a study by Blanca et al. (1994), hierarchical stimuli were placed either in the

right visual field or the left visual field for a time period of either 50, 100, or 200ms.

Participants were asked whether a target was present or absent. On target present

trials, the target could appear at the global level, the local level, or both levels.

Blanca et al. (1994) found that there was a RH (left visual field) accuracy advantage

for detecting the target when it was presented at the global level, and a LH (right

visual field) accuracy advantage when the target was presented at the local level,

consistent with the predicted asymmetries. However, of most interest is that these

accuracy advantages were found only when the stimulus exposure duration was

50ms, not when it was 100 or 200ms. Blanca et al. (1994) concluded that the

demonstration of hemispheric asymmetries for global and local processing in healthyindividuals is complex and may depend on specific experimental conditions. They

suggest that the common denominator necessary to demonstrate hemispheric spe-

cialization for global and local processing may be a reduction of stimulus visibility.

Boles and Karner (1996) further tested the stimulus visibility hypothesis. The

stimuli used in their experiment (Experiment 3) were hierarchical figures presented

bilaterally (i.e., simultaneously in both visual fields), for either 33 or 100ms. By

decreasing the exposure duration to 33ms (as compared to Blanca et al.�s 50ms),

they hoped to produce an even stronger test of the stimulus visibility hypothesis.Participants were asked to attend to either the global or local level and to report the

letter presented at that level. The results of this experiment were not, however,

consistent with Blanca et al.�s (1994). In fact, Boles and Karner�s (1996) results forthe accuracy data indicated that at both exposure durations, there was a RH (left

visual field) advantage for processing the local elements (opposite to the predicted

results); this advantage was significant for the 33ms condition and marginally sig-

nificant for the 100ms condition. Although there were no statistically significant

effects for the response time data, the pattern of results indicated a RH response timeadvantage both for global (visual field diff.¼ 28ms) and local (visual field

diff.¼ 42ms) processing. Thus, the predicted asymmetries were not demonstrated at

either the shorter (33ms) or the longer (100ms) exposure duration.

Boles and Karner (1996) concluded that the results are consistent with previous

findings that the RH has a general advantage over the LH under degraded stimulus

conditions (Bradshaw & Nettleton, 1983; Bryden & Allard, 1976; Hellige, 1980).

They argued that consistent with this explanation is the greater RH advantage at the

33ms exposure duration when participants were asked to attend to the small localletters (i.e., the most impoverished condition). Thus, according to this explanation,

the hemispheric asymmetry is more a function of perceptual characteristics than with

global or local processing per se. Blanca et al. (1994), however, contend that the

findings in their own study argue against the hypothesis that the hemispheric

asymmetries are simply due to the fact that the RH has been shown to be more

specialized for processing perceptually degraded stimuli. They argue that if this were

D.L. Evert, M. Kmen / Brain and Cognition 51 (2003) 115–142 117

the case, then shorter exposure durations should favor RH processing regardless of

whether global or local processing is involved, and longer exposure durations should

favor LH processing, and this was not the case in their study.

Taken together, the two studies that have assessed the effects of an exposure

duration manipulation on hemispheric asymmetries for global and local processing

found quite discrepant findings and hence proposed two very different hypotheses to

account for the pattern of results found in each of their studies. One should note that

there were methodological differences between the two studies. For example, Blancaet al. (1994) used a divided attention task and Boles and Karner (1996) used a se-

lective attention task. Because some behavioral studies have found the predicted

asymmetries using selective attention tasks (e.g., Martin, 1979; Robertson et al.,

1993; Yovel et al., 2001) and others have found them using divided attention tasks

(Blanca et al., 1994; Sergent, 1982; Yovel et al., 2001), it is unlikely that this

methodological difference contributed significantly to the discrepant results between

the two studies. Another methodological difference was that Blanca et al. (1994)

presented the stimuli to either the left or right visual field, while Boles and Karner(1996) presented the stimuli bilaterally. Although many studies of global/local pro-

cessing present stimuli unilaterally, Boles (1991, 1994, 1995) has found that bilateral

presentations of stimuli lead to reliable hemispheric differences in a number of tasks.

Thus, it is also unlikely that this methodological difference can account for the

difference in the pattern of results.

Clearly, definitive conclusions regarding the relationship between exposure du-

ration and global/local processing asymmetries based only on these two studies are

premature. Continued investigation of this relationship allows for further testing ofthe two hypotheses presented here: (1) that increased task demands (that possibly

limit stimulus visibility) are necessary to demonstrate expected hemispheric asym-

metries for global and local processing (hereafter referred to as the task demand

hypothesis) and (2) that hemispheric asymmetries under degraded conditions favor

RH specialization regardless of whether global or local processing is engaged (RH

degradation hypothesis).

In evaluating these two hypotheses, it is important to consider that they may not, in

fact, be mutually exclusive, which may account for the discrepant results mentionedabove. Specifically, the demonstration of hemispheric asymmetries for global and local

processing may be primarily manifested within a limited temporal range. Because of

the efficiency with which an intact brain can process information, and because hemi-

spheric specialization of function is relative, not absolute, there may be an upper ex-

posure duration threshold above which either hemisphere can perform the task

efficientlywithout the need to ‘‘call upon’’ themore specialized hemisphere.Hence, one

would not expect to see the predicted asymmetries. Furthermore, there may be some

lower exposure duration threshold belowwhichpredicted hemispheric asymmetries forglobal and local processing alsomay no longer be evident. In otherwords, theremay be

some point at which it is difficult to demonstrate asymmetries for global/local pro-

cessing per se because task demands are simply too difficult, even for the more spe-

cialized hemisphere. Itmay be at this point that theRH ‘‘takes over’’ and demonstrates

a general advantage for processing the perceptually degraded stimuli regardless of

whether attention is directed to the global or local level of the stimulus.

The experiments presented here were designed to further test these hypotheses

regarding the relationship between stimulus exposure duration and hemisphericspecialization for global and local processing. A wider range and a larger sample of

exposure durations were used across the experiments: 27, 40, 53, 67, 80, and 147ms

(due to the refresh rate of the computer monitor we were unable to replicate the 33

and 50ms exposure durations used in other studies). We expected that extending this

range would allow for a more sensitive and extensive test of the effects of exposure

duration on asymmetries for global and local processing, and would specifically


allow us to assess whether or not there is a critical temporal window within which

hemispheric asymmetries for global and local processing can be demonstrated.

The same general methods and procedure were used in each of the experiments.

Hierarchical letterforms were presented unilaterally to either the left or right visual

field and participants were asked to report either the global or local letter (depending

on the condition). In Experiment 1, we assessed global and local processing at ex-

posure durations of 53 and 147ms. In Experiment 2, we used 40, 53, and 80ms. And,

in Experiment 3, we used 27, 40, and 67ms. The 53ms condition in Experiment 2 wasincluded in hopes of replicating the results for this condition in Experiment 1 and the

40ms condition in Experiment 3 was included in hopes of replicating the results for

this condition in Experiment 2. The other exposure durations were used to expand

the range of durations tested. Furthermore, given the inconsistent findings across

studies in assessing hemispheric asymmetries, a secondary goal of ours was to further

check for reliability of the results within our own laboratory. Thus, each of the three

original experiments was replicated: Experiments 1-R, 2-R, and 3-R (R, replication).

Within the global/local processing literature, LH specialization for local pro-cessing is most often operationally defined as faster and/or more accurate responding

to targets presented in the right visual field relative to the left visual field, whereas

RH specialization for global processing is defined by the opposite pattern of results.

According to the task demand hypothesis, a LH-local advantage and a RH-global

advantage are expected to appear only at shorter exposure durations and/or to be of

a larger magnitude at shorter durations than at longer durations. According to the

RH degradation hypothesis, RH specialization is expected at shorter exposure du-

rations regardless of level of processing.

2. Experiments

2.1. Materials and methods

2.1.1. Participants

The participants included Skidmore College undergraduates, undergraduatesfrom other institutions who were enrolled in a summer research program in the

psychology department, high school students who were enrolled in other Skidmore

summer programs, and volunteers from the Skidmore community. Participants

during the academic year received credit towards their Introduction to Psychology

research requirement and participants during the summer were paid $4 each. A

different group of participants was used for each experiment. All of the participants

provided informed consent before beginning the study.

A handedness questionnaire and a brief demographic and medical history inter-view were administered to each participant. All participants were required to meet

the following criteria: right-handed, normal or corrected-to-normal vision, and no

history of a lazy eye, learning disability, mental illness, or neurological impairment.

Table 1 presents for each of the six experiments the number of participants, the mean

age and age range of the participants, and the number of females and males tested.

2.1.2. Apparatus and stimuli

A power Macintosh 6500 with a high-resolution 15-in. color monitor (800� 600,75Hz, Mac Std Gamma, refresh rate¼ 13.3ms) was used to present the stimuli and

record the responses. Millisecond timing of stimulus presentation and response was

controlled by PsychLab (Gum, 1997). A PsyScope button box (MacWhinney, 1996)

was used to register the participants� responses. The participants placed their heads

in an opthamalogic chin rest to ensure that their heads would not move throughout

the task.


The stimuli consisted of hierarchical letterforms constructed out of the letters H

and I (black letters presented on a white background). The size of the global letterwas 4.0� (width)� 6.1� (height) and the sizes of the local elements were 0:46�� 0:64�.The distance between each of the local letters (vertically and horizontally) was 0.30�.These dimensions are very similar to those used by Blanca et al. (1994). The lumi-

nance of the black level used for the stimuli was 0.17 cd/m2 and the luminance of the

white level used for the background was 110.07 cd/m2, as measured by a ColorVision

spectraphotometer (OptiCal, 2002). The total average luminance, which takes into

consideration the ratio of white to black pixels for a typical stimulus, was also

measured by randomly sampling across the stimulus; this value was 99.93 cd/m2.The first four trials of each block were used to allow the participants to acclimate

themselves to the task. These four trials were excluded from the final data analysis.

Of the remaining trials within a block, half of the time the letterform was presented

in the right visual field and the other half of the time it was presented in the left visual

field. For targets presented in each visual field, on half of the trials the stimuli were

consistently mapped (i.e., a large H made of small H�s, and a large I made up of

smaller I�s), and on the other half they were inconsistently mapped (i.e., a large H

made up of small I�s, and a large I made up of smaller H�s) (see Fig. 1). Within eachmapping condition, half of the time the global letter was an H and the other half

of the time the global letter was an I. Thus, there were eight possible stimulus

presentation conditions (e.g., consistently mapped global H presented in the LVF;

Fig. 1. Examples of the stimuli used in experiments: inconsistently mapped stimuli; consistently mapped

stimuli.

Table 1

Participant demographics for each of the experiments

Participants Mean age Age range Females/males

Experiment 1 (53, 147ms) n ¼ 38 18 years 16–24 years (unavailable)

Experiment 1-Ra n ¼ 30 18 years 17–19 years 25 Females, 5 males

Experiment 2 (40, 53, 80ms) n ¼ 23 23 years 18–50 yearsb 14 Females, 9 males

Experiment 2-R n ¼ 35 20 years 15–24 years 20 Females, 15 males

Experiment 3 (27, 40, 67ms) n ¼ 24 22 years 16–22 years 17 Females, 7 males

Experiment 3-R n ¼ 24 19 years 17–39 years 18 Females, 6 males

aR, replication experiment.bWithout the 50-year-old participant, the mean age of the remaining participants was 22 years (range

18–36).


inconsistently mapped global I [with local H�s] presented in the RVF). Within each

block of trials, each of the eight conditions was repeated 10 times for those exper-

iments in which only two exposure durations were used (Experiments 1 and 1-R), or

repeated 6 times for those experiments in which three exposure durations were used

(Experiments 2, 2-R, 3, and 3-R). The trial order within each block was randomized

with the criterion that no more than two trials for any of the eight stimulus condi-

tions were consecutively presented.

2.1.3. Procedure

Participants sat 57 cm away from the screen. First, a black fixation point appeared

in the center of the screen for 1500ms. The participants were instructed to keep their

eyes focused on the center of the screen throughout the task. After an inter-stimulus

interval (ISI) of 100ms, either a consistently or an inconsistently mapped hierar-

chical letterform was laterally presented (i.e., either in the left or right visual field).

The inner edge of the hierarchical letterform was presented 2.0� of eccentricity away

from the central fixation point. These figures were presented for a time period of 53or 147ms (Experiments 1 and 1-R), 40, 53, or 80ms (Experiments 2 and 2-R), or 27,

40, or 80ms (Experiments 3 and 3-R).

For half of the experimental blocks of trials, participants were instructed to in-

dicate as quickly and accurately as possible if the global letter was an H or an I by

pressing the corresponding button with the index finger of their right hand (global

attention condition). For the other half, participants were asked to indicate as

quickly and accurately as possible if the local letter was an H or an I by pressing the

corresponding button on the response box (local attention condition). One globalattention block of trials and one local attention block of trials were presented for

each exposure duration condition. Approximately half of the participants were

randomly assigned to complete the global attention task first at each exposure du-

ration and the others were assigned to complete the local attention condition task

first. Within each condition, the order of the different exposure duration blocks was

counterbalanced. The H and I buttons were horizontally aligned and the letter-to-

button correspondence was also counterbalanced across participants.

Participants were given a short practice block prior to each attention conditiontask (global and local) to ensure that they understood the directions and were able to

perform the task. The first practice block consisted of 16 trials and the second

practice block consisted of 8 trials. The participants completed two experimental

blocks at each exposure duration. Each block lasted approximately 4 1/2min and

rest periods were given between each block. Participants were debriefed upon

completion of the experiment.

3. Results

3.1. Response time analyses

The following trials were excluded from the response time analysis: the first four

trials of each block, trials in which response times were more than two standard

deviations from the mean within each experimental condition (outliers), and trials

with incorrect responses. Separate repeated measures analyses of variance (ANO-VA�s) were performed on the mean correct response time data (reported in milli-

seconds) for each exposure duration condition within each experiment (this resulted

in 16 different analyses, i.e., two analyses both for Experiment 1 and 1-R, and three

analyses for Experiments 2, 2-R, 3, and 3-R). A preliminary analysis for each ex-

periment revealed that the factor of Target Letter did not alter the interpretation of

the results related to the hypotheses of this study, thus all subsequent analyses were


collapsed across this variable. The three within-subjects variables were Target Level

(attention to either the local or global letter), Visual Field in which the hierarchical

letterform was presented (left visual field or right visual field), and Mapping (con-

sistent, inconsistent). Exposure duration was not included as a factor because dif-

ferent combinations of exposure durations were used across the experiments and we

were not interested in whether the particular combination of durations used within

an experiment had a differential effect. Rather, we were most interested in comparing

across the different experiments to specify the range of durations within whichhemispheric asymmetries can be found and thus conducted the planned comparisons

within each exposure duration condition.

Although the primary interest of this report was to present findings related to

hemispheric specialization for global and local processing at different exposure du-

rations, the findings related to global precedence and inter-level interference effects

are reported following the presentation of results with respect to hemispheric

asymmetries.

3.1.1. Hemispheric asymmetries

The means and standard errors (SE) for each experimental condition related to

hemispheric asymmetries are presented in Tables 2–4. Also included in these tables

are the results for the Target Level�Visual Field interaction and, when this inter-

action was statistically significant, the individual means comparisons.

These analyses indicated that under those conditions in which statistically sig-

nificant hemispheric asymmetries were found, the results were always in the expected

direction (i.e., a LH advantage for local processing and a RH advantage for globalprocessing). Across the different exposure duration conditions, a LH advantage for

local processing was found more frequently (eight times) than a RH advantage for

global processing (two times).

The LH-local advantage was primarily found between the exposure durations of

53 and 80ms. The most consistent finding was that a LH-local advantage was found

for each 53ms exposure duration condition (Experiments 1, 1-R, 2, and 2-R) and for

each 67ms exposure duration condition (Experiments 3, 3-R) tested. At one of the

two 80ms conditions, this LH-local advantage was marginally significant (Experi-ment 2-R) and there was a significant LH-local advantage for one of the four 40ms

conditions (Experiment 3-R). A RH-global advantage was found in only two in-

stances: one of the 67ms conditions (Experiment 3-R) and one of the 40ms condi-

tions (Experiment 2). There was only one instance in which both a LH-local and a

RH-global advantage were found at the same exposure duration (67ms: Experiment

3-R). Finally, no asymmetries were found at the longest (147ms: Experiments 1, 1-R)

or shortest (27ms: Experiments 3, 3-R) exposure durations tested.

In comparing the results for the original and replication experiments, the findingsfor Experiment 1 were fully replicated in Experiment 1-R. In both cases, a LH-local

advantage was found for the 53ms condition and no hemispheric asymmetries were

found for the 147ms condition. For Experiments 2 and 2-R, a LH-local advantage

was found for the 53ms condition; however, the findings for the 40 and 80ms

conditions differed for each experiment. And, for Experiments 3 and 3-R, the ab-

sence of a hemispheric asymmetry was found for the 27ms condition; however, the

results for the 40 and 67ms conditions differed for each experiment.2

2 It should be noted that the use of only right-handed responses, while problematic for explaining main

effects of visual field, is not problematic for the interpretation of the results presented here because only

interactions between Visual Field and Target Level were used as evidence for hemispheric asymmetries in

global and local processing.


Table 2

Hemispheric asymmetry results for Experiments 1 and 1-R (including mean response times and standard errors for each condition, and results from ANOVA data analyses)

Local target level Global target level Target level�Visual field interaction Summary

Experiment 1

53ms LVF > RVF LVF ¼ RVF F ð1; 37Þ ¼ 7:00, p < :05 Local: LH advantage

659(19) 643(19) 565(16) 562(16) Global: No asymmetry

[F ð1; 37Þ ¼ 19:52, p < :001] [F ð1; 37Þ < 1]

147ms LVF RVF LVF RVF F ð1; 37Þ ¼ 1:72 Local: No asymmetry


Experiment 1-R



[F ð1; 29Þ ¼ 6:55, p < :05] [F ð1; 29Þ < 1]



LVF, left visual field presentation of hierarchical letterform; RVF, right visual field presentation; LH, left hemisphere; RH, right hemisphere. Standard errors are presented in ( ).

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Table 3

Hemispheric asymmetry results for Experiments 2 and 2-R


Experiment 2

40ms LVF ¼ RVF LVF < RVF F ð1; 22Þ ¼ 4:01, p < :05 Local: No asymmetry

614(24) 610(27) 575(23) 594(22) Global: RH advantage

[F ð1; 22Þ < 1] [F ð1; 22Þ ¼ 5:98, p < :05]



[F ð1; 22Þ ¼ 10:09, p < :01] [F ð1; 22Þ < 1]



Experiment 2-R





[F ð1; 34Þ ¼ 15:56; p < :001] [F ð1; 34Þ < 1]



[F ð1; 34Þ ¼ 3:27, p < :08] [F ð1; 34Þ ¼ 1:72]

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Table 4

Hemispheric asymmetry results for Experiments 3 and 3-R


Experiment 3



40ms LVF RVF LVF RVF F ð1; 23Þ < 1 Local: No asymmetry




[F ð1; 23Þ ¼ 4:21, p < :05] [F ð1; 23Þ ¼ 2:42]

Experiment 3-R

27ms LVF RVF LVF RVF F ð1; 23Þ < 1 Local: No asymmetry




[F ð1; 23Þ ¼ 8:70, p < :01] [F ð1; 23Þ ¼ 1:67]

67ms LVF > RVF LVF < RVF F ð1; 23Þ ¼ 7:31, p < :01 Local: LH advantage

626(27) 615(28) 576(22) 604(32) Global: RH advantage

[F ð1; 23Þ ¼ 5:56, p < :05] [F ð1; 23Þ ¼ 4:33, p < :05]

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3.1.2. Global precedence and inter-level interference effects

The means and standard errors (SE) for each experimental condition related to

global precedence and interference effects are presented in Tables 5–7. Also included

in these tables are the ANOVA results for the factors of Target Level, Mapping, and

the Target Level�Mapping interaction. Means comparisons are also presented in

this table when the interaction was statistically significant.

The main concern was to ensure that the mapping of the target did not affect the

interpretation of the results regarding hemispheric asymmetries. Across the 16 dif-ferent analyses, there was only one instance in which the Target Level�Visual

Field�Mapping interaction was significant: Experiment 3 at the 67ms exposure

duration [F ð1; 23Þ ¼ 7:47, p < :05]. Further analyses indicated that this interaction

was due to the fact that the Visual Field � Mapping interaction was not significant

for the local target level condition ½F ð1; 23Þ ¼ :01�, but was significant for the globaltarget level condition [F ð1; 23Þ ¼ 6:89, p < :05]. For consistently mapped targets,

there was no significant hemispheric asymmetry (left visual field¼ 637ms, right vi-

sual field¼ 627ms) ½F ð1; 23Þ ¼ :92�. For inconsistently mapped targets, however,there was a significant RH (left visual field) advantage (left visual field¼ 626ms,

right visual field¼ 666ms) [F ð1; 23Þ ¼ 6:19, p < :05]. Thus, when participants were

asked to report the global letter, there was a significant RH advantage for incon-

sistently mapped targets, but not consistently mapped targets. When participants

were asked to report the local letter, there were no hemispheric advantages for either

the consistently or inconsistently mapped targets. (It should be noted that this

pattern of results was obtained for only one of the two 67ms exposure duration

conditions; for Experiment 3-R, there was no significant three-way interaction.)Because only 1 of the analyses 16 analyses showed a significant interaction with

this variable and because the results for the one interaction that was significant were

consistent with the predicted asymmetry (i.e., a RH advantage in the global pro-

cessing condition), the effects of mapping do not alter the interpretation of results for

hemispheric asymmetries.

3.2. Error analyses

The error rate data were also subjected to statistical analysis to assess hemispheric

asymmetries for the following reasons: (1) other researchers have found hemispheric

differences in the error data, but not in the response time data (e.g., Blanca et al.,

1994; Boles & Karner, 1996), so we wanted to be able to compare the results for the

two dependent measures, (2) we wanted to ensure that any significant results in the

response time analysis were not due to speed-accuracy tradeoffs (SATO�s), and (3)

according to the RH degradation hypothesis, we would expect to find increased error

rates at shorter exposure durations.The overall error rates (and standard errors) for each exposure duration condition

within each experiment are presented in Table 8. In general, the error rates were

quite small; the highest error rate did not exceed 2.5%. It could be argued that be-

cause of the small error rates, the data cannot meaningfully be submitted to an

ANOVA, nor can interaction contrasts be properly tested. However, for the reasons

mentioned above, we analyzed the results for comparative purposes.

As can be seen in Table 8, the error rates did not significantly differ across the

different exposure duration conditions within each experiment. In other words, errorrates were not significantly greater for the shorter than for the longer exposure

duration conditions within each experiment. To assess hemispheric asymmetries, the

Target Level � Visual Field interaction was evaluated within each experiment at

each exposure duration. As can be seen in Table 9, only two of the interactions were

significant: the 40ms [F ð1; 34Þ ¼ 4:96, p < :05] and 53ms [F ð1; 34Þ ¼ 5:33, p < :05]conditions in Experiment 2-R. In both cases, there were no hemispheric asymmetries


Table 5

Global precedence and interference effect results for Experiments 1 and 1-R (including mean response times and standard errors for each condition, and results from ANOVA data analyses)

Local target level Global target level Target level

Mapping Target level�mapping

Summary

Experiment 1

53ms Consis < Incon Consis < Incon F ð1; 37Þ ¼ 24:47, p < :0001 GP

619(19) 682(19) 556(16) 570(16) F ð1; 37Þ ¼ 127:09, p < :0001 Asymmetric IE

F ð1; 37Þ ¼ 29:60, p < :0001 Local IE¼ 63

[F ð1; 37Þ ¼ 74:36, p < :0001� [F ð1; 37Þ ¼ 17:92, p < :0001] Global IE¼ 14



F ð1; 37Þ ¼ 25:79, p < :0001 Local IE¼ 66

[F ð1; 37Þ ¼ 101:14, p < :001] [F ð1; 37Þ ¼ 20:44, p < :0001] Global IE¼ 21

Experiment 1-R



F ð1; 29Þ ¼ 12:35, p < :001 Local IE¼ 65

[F(1,29)¼ 40.27, p < :0001] [F ð1; 29Þ ¼ 5:47, p < :05] Global IE¼ 15



F ð1; 29Þ ¼ 7:02, p < :01 Local IE¼ 64


Consis., consistently mapped hierarchical letterforms (global and local forms the same); Incon., inconsistently mapped hierarchical letterforms (global and local forms differ); GP, global

precedence (significantly faster RTs on global than local trials); IE, interference effect (RT on inconsistent trials)RT on consistent trials).

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Table 6

Global precedence and interference effect results for Experiments 2 and 2-R



Summary

Experiment 2

40ms Consis < Incon Consis ¼ Incon F ð1; 22Þ ¼ 1:62 No GP


F ð1; 22Þ ¼ 19:59, p < :001 Local IE¼ 52

[F ð1; 22Þ ¼ 26:55, p < :0001] [F ð1; 22Þ < 1] Global IE ¼ �5

53ms Consis < Incon Consis ¼ Incon F ð1; 22Þ < 1 No GP


F ð1; 22Þ ¼ 33:90, p < :0001 Local IE¼ 71

[F ð1; 22Þ ¼ 57:54, p < :0001] [F ð1; 22Þ ¼ 1:10] Global IE ¼ 9

80ms Consis < Incon Consis ¼ Incon F ð1; 22Þ < 1 No GP


F ð1; 22Þ ¼ 44:01, p < :0001 Local IE¼ 75

[F ð1; 22Þ ¼ 63:56, p < :0001] [F ð1; 22Þ < 1] Global IE¼ 2

Experiment 2-R

40ms Consis Incon Consis Incon F ð1; 34Þ ¼ 22:19, p < :0001 GP

691(37) 731(38) 589(25) 627(30) F ð1; 34Þ ¼ 25:49, p < :0001 Symmetric IE

F ð1; 34Þ < 1 Local IE¼ 40




F ð1; 34Þ < 1 Local IE¼ 17

[F ð1; 34Þ ¼ 2:05] [F ð1; 34Þ ¼ 2:97] Global IE¼ 16



F ð1; 34Þ < 1 Local IE¼ 34

[F ð1; 34Þ ¼ 4:60, p < :05� [F ð1; 34Þ ¼ 6:17, p < :05] Global IE¼ 17

128

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Global precedence and interference effect results for Experiments 3 and 3-R



Summary

Experiment 3



F ð1; 23Þ < 1 Local IE¼ 47


40ms Consis < Incon Consis ¼ Incon F ð1; 23Þ ¼ 21:71, p < :0001 GP


F ð1; 23Þ ¼ 4:25, p < :05 Local IE¼ 50

[F ð1; 23Þ ¼ 15:89, p < :001] [F ð1; 23Þ ¼ 1:32] Global IE ¼ 11



F ð1; 23Þ ¼ 1:32 Local IE¼ 32


Experiment 3-R



F ð1; 23Þ ¼ 6:87, p < :05 Local IE¼ 47




F ð1; 23Þ ¼ 1:44 Local IE¼ 45


67ms Consis Incon Consis Incon F ð1; 23Þ ¼ 2:00 No GP


F ð1; 23Þ ¼ 1:16 Local IE¼ 45

[F ð1; 23Þ ¼ 32:85, p < :0001] [F ð1; 23Þ ¼ 2:55] Global IE¼ 26

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Table 8

Error rates (and standard errors) for each of the experiments as a function of exposure duration condition

Error rate (SE) ANOVA for factor of exposure duration

Experiment 1

53ms 1.20 (.20) F ð1; 37Þ ¼ 2:94

147ms 0.81 (.16)

Experiment 1-R

53ms 1.23 (.29) F ð1; 29Þ < 1

147ms 1.06 (.40)

Experiment 2

40ms 0.68 (.22) F ð2; 44Þ < 1

53ms 0.68 (.23)

80ms 1.27 (.62)

Experiment 2-R

40ms 1.88 (.29) F ð2; 68Þ ¼ 1:61

53ms 2.50 (.49)

80ms 1.67 (.34)

Experiment 3

27ms 1.50 (.36) F ð2; 46Þ ¼ 1:63

40ms 1.68 (.54)

67ms 0.95 (.35)

Experiment 3-R

27ms 1.26 (.34) F ð2; 46Þ ¼ 2:78

40ms 1.74 (.43)

67ms 0.82 (.19)

Table 9

ANOVA results regarding hemispheric asymmetries for error rate data from each of the experiments

Target level� visual field

Experiment 1

53ms F ð1; 37Þ ¼ 3:00

147ms F ð1; 37Þ < 1

Experiment 1-R

53ms F ð1; 29Þ < 1

147ms F ð1; 29Þ ¼ 3:54

Experiment 2

40ms F ð1; 22Þ < 1

53ms F ð1; 22Þ < 1

80ms F ð1; 22Þ < 1

Experiment 2-R

40ms F ð1; 34Þ ¼ 4:96; p < :05a

53ms F ð1; 34Þ ¼ 5:33; p < :05a

80ms F ð1; 34Þ < 1

Experiment 3

27ms F ð1; 23Þ < 1

40ms F ð1; 23Þ ¼ 3:03

67ms F ð1; 23Þ ¼ 2:00

Experiment 3-R

27ms F ð1; 23Þ < 1

40ms F ð1; 23Þ < 1

67ms F ð1; 23Þ ¼ 1:00aMeans comparisons presented in text.


in error rates for the global attention condition (40ms: ½F ð1; 34Þ ¼ 1:13�; 53ms:

½F ð1; 34Þ ¼ 0:27�Þ. In the local attention condition, however, there was a significant

LH advantage at both exposure durations (40ms: [F ð1; 34Þ ¼ 5:10, p < :05]; 53ms:

[F ð1; 34Þ ¼ 4:96, p < :05]). In other words, for the 40ms condition, the error rate for

right visual field local targets (1.31%) was significantly lower than the error rate for

left visual field local targets (2.86%); for the 53ms condition, the error rate for right

visual field local targets (2.02%) was also significantly lower than the error rate for

left visual field local targets (4.29%). Both of these asymmetries are in the expecteddirection.

An examination of the error rate data indicates that the patterns of results for the

response time data were not due to SATO�s. For the majority of the analyses, no

asymmetries were detected in the error rate data. For the two analyses that did find

significant asymmetries, the results do not support a SATO. Recall that for the 53ms

condition, a LH-local advantage was found in the response time data. Thus, for this

condition, response times were faster, and error rates were smaller, for right visual

field local targets. For the 40ms condition in Experiment 2-R, no asymmetries werefound in the response time data.

Furthermore, the fact that error rates did not significantly differ as a function of

exposure duration suggests that stimulus visibility per se, as suggested by Blanca

et al. (1994), may not adequately account for differences in the pattern of asym-

metries across different exposure durations. If stimulus visibility were being affected,

then significantly increased error rates for the shorter exposure duration conditions

would be expected. These findings are also important to consider when evaluating

the RH degradation hypothesis (discussed below).

4. General discussion

The experiments presented here were designed to further evaluate the relationship

between task demands, specifically target exposure duration, and hemispheric

asymmetries for global and local attentional processing. In two previous experiments

that had assessed this relationship, conflicting results were obtained and differenthypotheses were proposed to account for the contradictory results. Blanca et al.

(1994) argued that as task demands are increased and stimulus visibility decreases,

there is increased likelihood of demonstrating hemispheric asymmetries for global

and local processing in behavioral studies with healthy individuals (task demand

hypothesis). They found predicted asymmetries for global and local processing at a

50ms duration, but not at a 100 or 200ms duration. Boles & Karner (1996), how-

ever, found a RH advantage for processing local stimuli at a 33ms exposure dura-

tion; they argued that this hemispheric difference at the shorter exposure durationreflects a general RH advantage for processing perceptually degraded stimuli (RH

degradation hypothesis).

These two hypotheses were further evaluated in the present set of studies. Six

different stimulus exposure durations (27, 40, 53, 67, 80, and 147ms) were tested in a

selective attention task in which hierarchical letterforms were presented unilaterally

to either the left or right visual field. Three main issues are considered in the discussion

of the results (keep in mind that these issues are not necessarily mutually exclusive): (1)

why were asymmetries for local processing demonstrated more often than asymme-tries for global processing, (2) do the results support the task demand and/or RH

degradation hypotheses, and (3) what conclusions can be made about the reliability

of demonstrating predicted asymmetries across different exposure duration condi-

tions, both within this set of studies and across studies from different laboratories?

A series of studies published by Yovel et al. (2001) is first described because their

findings are important to consider in addressing these issues. These researchers also


attempted to explain the discrepancy in demonstrating hemispheric asymmetries for

global and local processing in behavioral studies with healthy individuals. Although

they did not assess the effects of exposure duration on hemispheric asymmetries, Yovel

et al. (2001) manipulated several other stimulus and task factors, including the saliency

of the global and local letters (GS¼ global letter more salient than local letter,

ES¼ global and local letters equally salient), attentional demands (focused/selective

vs. divided), and response mode (go-no go vs. two-choice). They hypothesized that

hemispheric asymmetries for global and local processing would be more reliablydemonstrated with ES stimuli (which would avoid potential ceiling effects using GS

stimuli in the processing of the global form and floor effects in the processing of the

local elements), on divided attention tasks (where each hemisphere can attend to its

preferred level, thus necessitating unpredictable switches of attention from that

hemisphere�s preferred level to a nonpreferred target level), and using a go-no go re-

sponse mode (which avoids spatial-compatibility effects that can arise in two-choice

tasks). They also used backward pattern masking to minimize interhemispheric

communication and a small stimulus eccentricity (0.5�) to reduce parafoveal stimulusdegradation. In each of their studies the hierarchical stimuli were presented for 100ms.

Across their first set of studies (which included a divided attention/go-no go task,

a focused attention/go-no go task, and a divided attention/two-choice task) they

found a RH advantage for global processing and a LH advantage for local pro-

cessing for all three tasks with the ES stimuli, and for the two divided attention tasks

with the GS stimuli (but no hemispheric asymmetries for the focused attention task

with GS stimuli). Although the asymmetries did not significantly interact with

stimulus type, they found that the effect size was larger for ES than GS stimuli. Theyalso found a trend toward larger hemispheric asymmetries on divided than on fo-

cused attention tasks using the go-no go response mode. In their second experiment,

Yovel et al. (2001) also included a focused attention/two-choice task, which is the

task used in our set of experiments. They found that hemispheric asymmetries for

global and local processing differed as a function of attentional demands. For the

divided attention task, there was a significant LH local advantage and a marginally

significant RH global advantage; for the focused attention task, there was a LH-local

advantage (the effect size of which was smaller than on the divided attention task),and no RH-global advantage. There was no systematic effect of response mode

across the experiments. In general, Yovel et al.�s (2001) findings emphasize the im-

portance of stimulus characteristics for detecting hemispheric differences in global

and local processing. The implications of their findings are considered below in the

discussion of the results from our set of studies.

4.1. Bias for demonstrating LH-local asymmetries

The present results indicated that, overall, a LH-local advantage was found more

consistently than a RH-global advantage. While no other studies have assessed such

a wide range of exposure durations, it is interesting to note that in other reported

studies there appears to be a bias to find LH-local asymmetries, either at the ex-

clusion of finding RH-global asymmetries (e.g., Christman & Weiner, 1997; see also

Hopkins, 1997, for an animal study) or under more conditions than those for RH-

global asymmetries (e.g., Martin, 1979; Yovel et al., 2001). Here, we consider a few

explanations for why such a bias might have existed in the present set of studies.It could be argued that the more consistent finding of a LH-local advantage may

be due to the fact that the stimuli used in these experiments were linguistic in nature,

and for most right handers, the LH is more specialized for linguistic processing.

However, other studies have found a LH advantage for local processing regardless of

whether the stimuli are linguistic in nature (Kimchi & Merhav, 1991; Versace &

Tiberghien, 1988; see also Fink et al., 1996, 1997a, 1997b, for functional imaging


evidence in which presentation of the stimuli was central and activations were lat-

eralized). Furthermore, if the pattern was simply due to the fact that the stimuli were

linguistic, then one would expect LH specialization regardless of the attention

condition. Thus, it is reasonable to assume that the results are due to attentional

processing and not to an artifact of the nature of the stimuli.

Another possible explanation for the bias in demonstrating local asymmetries

may have to do with the definition of RH specialization for global processing. In the

present study, RH specialization for global processing was operationally defined as aresponse time advantage for left visual field targets under global target level con-

ditions. However, within the literature on directing spatially based attention, a

somewhat different interpretation of RH specialization for attentional processing has

been proposed. Specifically, physiological (Corbetta, Miezin, Shulman, & Petersen,

1993; Heilman & Van Den Abell, 1980; Proverbio, Zani, Gazzaniga, & Mangun,

1994) and behavioral (Evert & Oscar-Berman, 2001; Roy, Reuter-Lorenz, Roy,

Copland, & Moscovitch, 1987) findings point to a specialized role of the RH in

attentional processing in that it appears to be able to mediate attention in a broaderregion of extrapersonal space, whereas the LH is more limited in that it directs at-

tention primarily to the right side of space (see also Halligan & Marshall, 1994).

Thus, according to this account of how the RH is implicated in attentional pro-

cessing, one should not expect to find a left visual field advantage for global pro-

cessing because the RH is able to direct attention to both sides of space; in other

words, there should be no visual field asymmetry. While this explanation is ap-

pealing, it still cannot explain why a RH-global advantage was found in a few cases

in the present study, as well as in other studies assessing global/local processinghemispheric asymmetries (e.g., Blanca et al., 1994; Martin, 1979; Van Kleeck, 1989).

Furthermore, attention is a multifaceted function, the components of which rely on a

distributed network of neural structures that orchestrate its operation (e.g., Rafal &

Robertson, 1995). For example, Egly, Rafal, Driver, & Yves (1994) found evidence

in a commissurotomized patient that the right parietal lobe plays a more important

role in shifting attention between different locations in space, while the left parietal

lobe is more critical in shifting attention between objects. We must be cautious,

therefore, in presuming that the mechanisms involved in the direction of spatiallybased attention are analogous to those involved in directing attention to a particular

level of an object within a region of space. Hence, it is not certain that an operational

definition of RH specialization that is appropriate for directing spatially based at-

tention is also appropriate for the type of attentional processing assessed in this set

of studies. The relationship of the mechanisms underlying these different forms of

directing attentional resources warrants further investigation.

Another possibility for why there was a bias in demonstrating local asymmetries

may have to do with stimulus characteristics, such as the sizes or density of thestimuli (i.e., the number and proximity of the local elements that comprise the global

figure). In fact, Yovel et al. (2001) point out that most studies of hemispheric

asymmetries in global and local processing use stimuli in which the global letter is

much more salient than the local letter. As mentioned previously, they propose that

the use of GS stimuli could lead to ceiling effects when processing the global form

and floor effects when processing the local form (and thus would minimize detection

of hemispheric asymmetries). As can be seen in Table 10, the dimensions of the

stimuli used in the present set of studies were more similar to Yovel et al.�s (2001) GSstimuli than to their ES stimuli. Recall that in their focused attention/two-choice task

with GS stimuli (Experiment 2) they found a LH local advantage, but no RH global

advantage. Perhaps, then, the bias to detect LH-local asymmetries in the present set

of studies can be attributed to the use of GS salient stimuli such that global pro-

cessing was as easy for the LH as for the RH. The use of such stimuli did not,

however, preclude the detection of LH-local asymmetries.


Further evidence for a bias in global processing can be found by assessing global

precedence effects. For the GS stimuli in the Yovel et al. (2001) study, response

times to global targets were significantly faster than response times to local targets

in both visual fields (although the global precedence effect was larger for stimuli

presented in the left visual field). For the ES stimuli, the results were not consistent:

for the divided attention/go-no go task they found global precedence in the left

visual field and local precedence in the right visual field, for the focused attention/

go-no go task they found no precedence effects in the left visual field, and localprecedence in the right visual field, and for the focused attention/go-no go task they

did not find any precedence effects in either visual field (note: they did not use ES

stimuli in the focused attention/two-choice task). Based on these results, it appears

that consistent global precedence (presumably from the use of GS stimuli) was

associated with smaller hemispheric asymmetry effect sizes. Although not the pri-

mary focus of this study, we also considered whether the phenomenon of global

precedence might help to explain the bias to find LH-local asymmetries. It is in-

teresting to note that global precedence was found for six of the eight conditions inwhich a LH-local advantage was found, but for neither of the conditions when a

RH-global advantage was found (see Table 11). Therefore, the global precedence

may have led to ceiling effects making the detection of RH-global asymmetries

more difficult. Because global precedence was also found in six out of the seven

cases when no asymmetries were detected, it is clear that global precedence effects

cannot be the sole explanation for more frequent detection of LH-local asymme-

tries in the present set of studies; specifically, exposure duration appears to be

another critical variable that influences the detection of such asymmetries. Furtherstudy is needed to compare situations in which either a global processing advan-

tage, a local processing advantage, or no processing advantage is clearly and

consistently demonstrated to assess whether such a bias influences the likelihood

and frequency of demonstrating local and global processing asymmetries, and

whether precedence effects reliably interact with task demand manipulations such as

exposure duration.

A final explanation for why there was a bias to detect LH-local asymmetries, and

a decreased sensitivity to detect RH-global asymmetries may be due to the fact thata focused attention task was used and, as Yovel et al. (2001) point out, focused

Table 10

Comparison of dimensions of hierarchical stimuli used in the present experiments, Yovel et al. (2001), and

Blanca et al. (1994)

Global

height

Global

width

Local

height

Local

width

Local/global

height ratio

Local/global

width ratio

Present experiment 6.1� 4.0� 0.64� 0.46� 0.105 0.115

Yovel et al. GS stimuli

(Experiment 2)

4.8� 2.9� 0.45� 0.38� 0.094 0.131

Yovel et al. ES stimuli

(Experiment 1)

3.9� 2.3� 0.50� 0.40� 0.128 0.174

Blanca et al. 5.8� 4.7� 0.57� 0.38� 0.098 0.081

GS, globally salient stimuli; ES, equally salient stimuli.

Table 11

Evidence supporting the phenomenon of global precedence across all experiments under conditions in

which local, global, or no asymmetries were found in the response time data

Overall global advantage

LH-local advantage (found in 8 instances) 6/8 (75%)

RH-global advantage (found in 2 instances) 0/2 (0%)

No asymmetries (found in 7 instances) 6/7 (86%)


attention tasks may be less sensitive than divided attention tasks in detecting

hemispheric asymmetries. This may also explain why Blanca et al. (1994) found both

a LH-local and a RH-global advantage at the 50ms exposure duration, whereas we

found only a LH-local advantage at 53ms, even though their stimulus parameters

were similar to ours (see Table 10).

It is clear from this discussion that no single variable can adequately explain the

bias to detect LH-local asymmetries in the present set of experiments. Rather, this

bias appears to be due to the interaction of several stimulus and task variables, in-cluding the saliency of the stimuli, precedence effects, and the nature of the attention

task.

4.1.1. Evaluation of the task demand and RH degradation hypotheses

The response time results indicated that no asymmetries were detected at the

longest (147ms) and shortest (27ms) exposure durations tested. The LH-local ad-

vantage was generally found within the middle range of exposure durations tested

(53–80ms), the most consistent finding being that it was detected at each of the 53and 67ms conditions tested. A RH-global advantage was found for only one of the

67ms conditions and only one of the 40ms conditions. And, finally, error rates did

not differ significantly as a function of exposure duration.

An evaluation of the evidence for the task demand hypothesis partially depends on

how the predictions of the hypothesis are specified. There are two ways to interpret

this hypothesis. Both interpretations predict that asymmetries should not be present

at longer exposure durations because task demands are simply too easy and either

hemisphere can efficiently perform both global and local processing. The two in-terpretations, however, differ with respect to what happens as task demands are

increased even further. According to one interpretation, as task demands are in-

creased (i.e., as exposure duration is decreased) there should be some point at which

the asymmetries should appear and these asymmetries should continue to be ap-

parent as task demands are increased even further. According to the other inter-

pretation, there may be a range of optimal stimulus durations within which the

predicted asymmetries can be demonstrated; that is, there may be some lower

threshold beyond which the task demands are simply too great and asymmetries forglobal and local attentional processing may no longer be apparent.

The results from the present set of studies are clearly not consistent with the first

interpretation (since asymmetries were not detected at 27ms, and a LH-local ad-

vantage was found for only one of the four 40ms conditions tested). The results are,

however, more consistent with the second interpretation, since asymmetries were

detected in the middle range of durations tested and there were no asymmetries at the

longest and shortest durations. These results, therefore, demonstrate a limited

temporal range within which predicted hemispheric asymmetries for global and localprocessing are demonstrated in healthy individuals using the task parameters of the

present study.

It is important to also take into consideration the error rate data when evaluating

the task demand hypothesis. Surprisingly, error rates did not significantly differ as a

function of exposure duration. Thus, the findings in the present set of studies argue

against Blanca et al.�s (1994) conclusions that a reduction in stimulus visibility per se

is necessary for demonstrating hemispheric asymmetries in global and local pro-

cessing; our results demonstrate asymmetries even under conditions in which stimulusvisibility does not appear to be affected. Furthermore, these findings suggest that the

existence of a lower threshold is not simply due to task difficulty. Thus, while the

results suggest a range of optimal durations within which asymmetries are demon-

strated, it is not yet clear exactly what is being affected by the exposure duration

manipulation that can account for the limits beyond which hemispheric asymmetries

for global and local processing are no longer evident in this set of studies.


The error rate data are also important to consider when evaluating the RH

degradation hypothesis. As mentioned in Section 1, one possible explanation for the

discrepant results between Blanca et al. (1994) and Boles & Karner (1996) is that

there might be a shift toward a RH advantage, regardless of level of processing, at

very short exposure durations due to degradation of the stimuli. However, to ade-

quately test the RH degradation hypothesis one needs to demonstrate that the stimuli

are, in fact, perceptually degraded. Again, because error rates did not differ as a

function of exposure duration, it appears that the quality of the percept was notsubstantially affected by the exposure duration manipulation. Thus, although RH

specialization in the present set of studies was only linked to global processing

(which argues against the RH degradation hypothesis), we could not rule out the

possibility for a shift towards RH specialization regardless of level of processing at

shorter exposure durations under degraded stimulus conditions.3

Consistent with the results from the present study, findings from a literature re-

view by Christman (1989) provide equivocal support for the RH degradation hy-

pothesis. He reviewed 30 years of research on the effects of perceptual characteristicson visual perceptual lateralization to test the hypothesis that characteristics that

reduce the availability of higher spatial frequencies (i.e., increased retinal eccen-

tricity, size, and blur, and decreased luminance and exposure duration) will impair

left hemisphere performance more than right hemisphere performance. Overall the

results indicated that variations in size and exposure duration yielded weaker results

with respect to the hypothesis than variations in the other perceptual characteristics

(i.e., eccentricity, luminance, and blur). Furthermore, while decreased size and ex-

posure duration both lead to degraded viewing conditions, a decrease in exposureduration tended to favor right hemisphere processing and a decrease in size tended to

favor left hemisphere processing.

In summary, the present results indicate that we can demonstrate differential

participation of the hemispheres in global and local processing in healthy individ-

uals, but that the conditions under which they are demonstrated are constrained;

specifically, the results indicate that, given the task parameters used here, asymme-

tries for global and local processing are present within a limited exposure duration

window. While the present results indicate that exposure duration is an importantvariable to consider in detecting asymmetries in healthy individuals, the conditions

under which asymmetries are reliably detectable likely depends on some optimum

combination of stimulus and task factors.4

4.1.2. Reliability of findings

An important issue to consider in evaluating any hypothesis to explain the effects

of a task demand manipulation on demonstrating asymmetries for global and local

processing is reliability, both within one�s own laboratory, as well as across studiesfrom different laboratories. To assess the reliability of the findings within our own

laboratory, we tested some exposure durations multiple times across the three ori-

ginal experiments, and we replicated each experiment.

The most reliable findings were that a LH-local advantage was found for each

53ms and each 67ms exposure duration tested and no asymmetries were found at

each 147 and 27ms exposure duration tested across the experiments. The upper and

3 It is possible that the low error rates overall may be due to the small stimulus set (i.e., H and I) used in

the present studies. While the use of response time was sensitive in detecting hemispheric differences in

global and local processing, perhaps a larger stimulus set would have more of an effect on error rates,

which would have allowed us to better assess the RH degradation hypothesis.4 Perhaps the small stimulus eccentricity and use of backward masking can account for the LH-local

asymmetry detected at the 100ms exposure duration used in Yovel et al.�s (2001) focused attention/two-

choice task.


lower boundaries for demonstrating the LH-local asymmetry, however, were less

reliable: a LH-local advantage was found in one instance at 80ms, but not in an-

other, and it was found in one instance at 40ms, but not in three others. The

demonstration of a RH-global advantage was idiosyncratic since it was found for

one of the four 40ms conditions, not at all for the 53ms conditions, and for one of

the two 67ms conditions. Across the replication experiments within this set of

studies, only Experiment 1-R fully replicated the results of Experiment 1.

The somewhat ‘‘fuzzy’’ boundaries for the upper and lower limits of the rangewithin which the asymmetries are demonstrated are not surprising. For example,

with respect to the upper exposure duration threshold, it is unlikely that there is an

exact millisecond duration above which asymmetries are never found and below

which asymmetries are always found. Such precision is unlikely for dynamic bio-

logical systems. The inexact nature of the boundary helps to explain why only Ex-

periment 1 was fully replicated in Experiment 1-R. In these two experiments there

was quite a large range between the two exposure durations used (i.e., 100ms).

Because the 53ms exposure duration appears to be clearly within the range and the147ms duration appears to be clearly outside of the range, the pattern of results

across the original (E1) and replication (E1-R) experiments were reliable. For Ex-

periments 2 and 3, however, there was a smaller range between the longest and

shortest exposure durations used (i.e., 40ms) and some of these durations appear to

fall near the boundaries. The most important finding for the task demand hypothesis

is that asymmetries were reliably found within the middle portion of this range and

were reliably absent well outside this range.

Our results partially replicate those of Blanca et al. (1994) (i.e., we found a LH-local advantage at 53ms, but not a RH-global advantage at this same exposure

duration), but do not replicate those of Boles & Karner (1996). When asymmetries

were found in the present set of studies, they were always in the predicted direction.

While a direct comparison of the present results to other studies is complicated by

variations in stimulus and task variables, it is possible that the failure to replicate the

Blanca et al. (1994) finding of a RH-global advantage at the 53ms duration may be

due to the fact that they used a divided attention task and we used a focused at-

tention task (see Yovel et al., 2001).One final point to consider in assessing the reliability of findings with respect to

the effects of exposure duration on global and local processing is whether the lu-

minance of the stimuli and its interaction with exposure duration may play a sig-

nificant role in the pattern of results both across and within studies. According to

Bloch�s Law, constant visual effect ðCÞ ¼ Intensity ðIÞ � Time ðT Þ. Two stimuli that

contain the same total energy (even if they are based on a different combination of

intensity and time values) will be equally detectable. Evidence suggests that Bloch�sLaw applies to simple stimuli and tasks (e.g., Kahneman & Norman, 1964; Raab &Fehrer, 1962). There is some evidence to suggest that Bloch�s Law also applies to

more complex stimuli (Loftus & Ruthruff, 1994), although it is not clear if it applies

to hierarchical stimuli used in global/local tasks. There is some disagreement re-

garding the exposure duration range within which Bloch�s Law holds. For the

photopic cone-dominated system, some argue that Bloch�s Law appears to hold only

for durations less than 50ms (Hood & Finkelstein, 1986; Regan, 2000), whereas

others contend that it holds for durations up to 100ms (Loftus & Ruthruff, 1994).

For the purposes of the present discussion, we adopt a conservative approach toexamine to possible consequences of Bloch�s Law on the interpretation of the results

reported here. If we assume for a moment that Bloch�s Law does hold for the

complex hierarchical stimuli and two-choice response task used in the present set of

studies, and if we assume that it holds for durations up to 100ms, then the rela-

tionship between stimulus intensity and exposure duration may be important to

consider in the present context for two reasons: (1) different findings across studies


using the same exposure durations may be explained by differences in luminance

values of the stimuli used in the experiments, and (2) given a wide range of exposure

durations for stimuli at the same luminance (as used in the present set of studies),

Bloch�s Law may apply to some durations and not others and, therefore, might

influence the interpretation of the results.

We first address the issue of comparing results across studies. Unfortunately the

luminance values for the stimuli used in the Boles & Karner (1996) and Blanca

et al. (1994) studies are unavailable (personal communication with D. Boles andM. Blanca). However, given that Blanca et al. (1994) used a tachistoscope and

Boles & Karner (1996) used a computer monitor for presentation of the stimuli, it

is likely that the luminance values of their stimuli were different (luminance tends

to be brighter with tachistoscopes). Thus, at the one exposure duration in common

to these two studies (100ms), it is possible that Boles & Karner�s (1996) stimuli

were less visible than Blanca et al.�s (1994) stimuli. Perhaps if the stimuli were

particularly degraded in the Boles & Karner (1996) study, this could account for

the trend for a RH advantage (because of the RH�s superiority in processingdegraded stimuli). Although definitive conclusions cannot be drawn without the

luminance values of the stimuli used in the experiments, there are two points that

call into question the extent to which luminance/duration interactions can ade-

quately explain the difference in the pattern of results between the two studies.

First, it is likely that the luminance of the stimuli used in our experiments were

more similar to those of Boles & Karner (1996) because both studies used

computer monitors for the presentation of the stimuli. However, the results of the

present study are more similar to those of Blanca et al. (1994), even though theyused a tachistoscope. Second, it seems unlikely that the stimuli in the Boles

& Karner (1996) study were significantly more degraded than the stimuli in other

studies that used computer monitors and a 100ms exposure duration (none of

which found RH specialization for local processing). Therefore, it is unlikely that

potential luminance differences could account for why they found results opposite

to the predicted asymmetries.

In our set of studies, the stimuli were all presented at the same luminance.

Again, if we adopt the assumptions indicated above, it is possible that Bloch�s Lawmay apply for some of our exposure durations, but not others. The question of

interest is whether Bloch�s Law can account for any of the findings in the present

set of studies. A basic tenet of Bloch�s Law is that at a given luminance, a shorter

exposure duration will decrease the visibility of the stimulus compared to a longer

exposure duration at the same luminance, and will increase the threshold for de-

tection. Although ours was not a threshold detection task, it is likely that this

decreased visibility would also result in increased error rates. However, in the

present set of studies error rates did not significantly increase with decreased ex-posure duration, so it is questionable whether Bloch�s Law applies here. Even if it

does apply, it likely only applies for the shorter durations. Regardless of the

mechanism (e.g., luminance duration/interactions, exposure duration only) that

explains the lower boundary above which asymmetries are detected, and below

which asymmetries are not detected, the main interpretation of the results remains

unchanged: given the task parameters of the set of studies, hemispheric asymme-

tries for global and local processing are reliably detected only within a limited

exposure duration range.Although stimulus/intensity relationships are important under certain circum-

stances, and one should consider this relationship in drawing general conclusions

across different studies assessing the effects of exposure duration, we do not think

that Bloch�s Law significantly changes the interpretation of the results presented

here. Further study is needed to determine whether this law even applies to the types

of stimuli and the task used in this set of experiments.


5. Conclusions

Including the present set of experiments, three studies have directly assessed the

relationship between stimulus exposure duration and global/local processing asym-

metries. The present set of studies extend the findings of Blanca et al. (1994) by

suggesting that there is a temporal range within which predicted asymmetries are

found, including both an upper and lower limit (this was especially true for local

processing). While the present results could not be used to resolve the discrepancybetween Blanca et al. (1994) and Boles & Karner (1996), all three studies converge by

highlighting the importance of reliably demonstrating predicted asymmetries and

emphasizing the need to further specify and clarify the conditions under which these

asymmetries appear in healthy individuals. Based on their set of studies, Yovel et al.

(2001) concluded that ‘‘the reliable perceptual asymmetries on the variety of tasks in

[their] studies, as well as the positive and negative results of previous investigations,

suggest that there is no single task factor that is critical for revealing or concealing

perceptual effects of hemispheric asymmetries. Rather, the probability of observingreliable asymmetries in favor of the RH-LVF for global perception and the LH-RVF

for local perception depends on various combinations of multiple task factors (e.g.,

ES letters, divided attention, backward masking, small eccentricity)’’ (p. 1383). We

agree with their conclusion and add stimulus exposure duration to their list of im-

portant task factors.

Questions still remain, however. With respect to our set of studies, what does it

mean that hemispheric asymmetries in global and local processing only emerge

within a limited range of exposure durations? More generally, is there some ‘‘for-mula’’ for a particular combination(s) of stimulus and task parameters that will lead

to the reliable detection of hemispheric asymmetries in healthy individuals and, if

there is, what does this mean? Do these findings mean that the hemispheric asym-

metries are always present, but only evident under certain experimental conditions,

or do they mean that the phenomenon exists only under very specific conditions and,

therefore, may potentially have little consequence for normal behavior?

Given the converging evidence, we believe that the two hemispheres do differen-

tially participate in global and local levels of processing in normal behavior. And wealso believe that while specialization for global and local processing exists, this does

not mean that this specialization is needed at all times. As we mentioned earlier,

because hemispheric asymmetries are relative, and because interhemispheric com-

munication in an intact brain is efficient, the more specialized hemisphere may be

needed only under certain demanding conditions (also see Yovel et al., 2001). But if

this phenomenon only has consequences for normal behavior under specific condi-

tions, this raises the question of why the hemispheres are differentially specialized for

global and local processing to begin with. In other words, what function doeshemispheric specialization for global and local processing serve if this specialization

is manifested only under certain limited conditions? We believe that this special-

ization serves to maintain efficient processing of information under those conditions

in which performance might otherwise be adversely affected. Although the present

studies points to a limited range within which the specialized hemisphere is ‘‘need-

ed,’’ it is likely that the parameters of the laboratory task used here underestimate

the information processing demands in our every day lives. Our senses are contin-

uously bombarded with different types of sensory information and we must con-tinuously select the relevant, important information from amongst the morass of

irrelevant information competing for our attentional and perceptual resources. Thus,

the increased efficiency in processing information by a specialized hemisphere is

likely even more pronounced outside of the laboratory setting.

Although the present set of studies was not designed to address these broad

questions, they do highlight the importance of stimulus and task variables in


detecting hemispheric differences in global and local processing. To the extent that it

is possible, future research on hemispheric specialization for global and local pro-

cessing may be able to address the broader questions outlined here.

Acknowledgments

This research was partially supported by a grant from the National Science

Foundation (Research Experience for Undergraduates, SBR-9820031) and a faculty

development grant from Skidmore College awarded to the first author. We thank

Mary Ann Foley for helpful comments on an earlier draft of the manuscript. We also

thank Flip Phillips for computer programming and technical assistance, and the

following students for assistance in data collection and analysis: Mary Bates, Carla

Edmonson, Alyson Lieban, Niki Michaelson, Stacie Richardson, Ingrid Sarmiento,

and Mimi Valderrama. Experiment 2 of the manuscript was the second author�ssenior thesis project at Skidmore College.

References

Alivisatos, B. W., & Wilding, J. (1982). Hemispheric differences in matching Stroop-type letter stimuli.

Cortex, 18, 5–21.

Banich, M. T., & Noll, E. L. (1993). Target detection in left and right hemispace: Effects of positional pre-

cueing and type of background. Neuropsychologia, 31, 525–545.

Blanca Mena, M. J. (1992). Can certain stimulus characteristics influence the hemispheric differences in

global and local processing? Acta Psychologica, 79, 201–217.

Blanca, M. J., Zalabardo, C., Gar�ıı-Criado, F., & Siles, R. (1994). Hemispheric differences in global and

local processing dependent on exposure duration. Neuropsychologia, 32, 1343–1351.

Boles, D. B. (1984). Global versus local processing: Is there a hemispheric dichotomy? Neuropsychologia,

22, 445–455.

Boles, D. B. (1991). Factor analysis and the cerebral hemispheres: Pilot study and parietal functions.

Neuropsychologia, 29, 59–90.

Boles, D. B. (1994). An experimental comparison of stimulus type, display type, and input variable

contributions to visual field asymmetry. Brain and Cognition, 24, 184–197, doi:10.1006/brcg.l994.1010.

Boles, D. B. (1995). Parameters of the bilateral effect. In F. L. Kitterle (Ed.), Hemispheric communication:

Mechanisms and models. Hillsdale, NJ: Erlbaum Associates.

Boles, D. B., & Karner, T. A. (1996). Hemispheric differences in global versus local processing: Still

unclear. Brain and Cognition, 30, 232–243, doi: 10.1006/brcg. 1996.0015.

Bradshaw, J. L., & Nettleton, N. C. (1983). Human cerebral asymmetry. Englewood Cliffs, NJ: Prentice-

Hall.

Bryden, M. P., & Allard, R. (1976). Visual hemifield differences depend on typeface. Brain and Language,

3, 191–200.

Christman, S. D., & Weiner, R. H. (1997). Hemispheric processing of form versus texture at the local level

of hierarchical patterns. Acta Psychologica, 96, 193–206.

Christman, S. (1989). Perceptual characteristics in visual laterality research. Brain and Cognition, 11, 238–

257.

Corbetta, M., Miezin, F. M., Shulman, G. L., & Petersen, S. E. (1993). A PET study of visuospatial

attention. Journal of Neuroscience, 13, 1202–1226.

Delis, D. C., Robertson, L. C., & Efron, R. (1986). Hemispheric specialization of memory for visual

hierarchical stimuli. Neuropsychologia, 24, 205–214.

Doyon, J., & Milner, B. (1991). Right temporal-lobe contribution to global visual processing.

Neuropsychologia, 29, 343–360.

Egly, R., Rafal, R., Driver, J., & Yves, S. (1994). Covert orienting in the split brain reveals hemispheric

specialization for object-based attention. Psychological Science, 5, 380–383.

Evert, D. E., & Oscar-Berman, M. (2001). Selective attentional processing and the right hemisphere:

Effects of aging and alcoholism. Neuropsychology, 15, 452–461.

Fagot, J., & Deruelle, C. (1997). Processing of global and local visual information and hemispheric

specialization in humans (Homo sapiens) and baboons (Papio papio). Journal of Experimental

Psychology: Human Perception and Performance, 23, 429–442.

Fink, G. R., Halligan, P. W., Marshall, J. C., Frith, C. D., Frackowiak, R. S. J., & Dolan, R. J. (1996).

Where in the brain does visual attention select the forest and the trees? Nature, 382, 626–628.


Fink, G. R., Halligan, P. W., Marshall, J. C., Frith, C. D., Frackowiak, R. S. J., & Dolan, R. J. (1997a).

Neural mechanisms involved in the processing of global and local aspects of hierarchically organized

visual stimuli. Brain, 120, 1779–1791.

Fink, G. R., Marshall, J. C., Halligan, P. W., & Dolan, R. J. (1999). Hemispheric asymmetries in global/

local processing are modulated by perceptual salience. Neuropsychologia, 37, 31–40.

Fink, G. R., Marshall, J. C., Halligan, P. W., Frith, C. D., Frackowiak, R. S., & Dolan, R. J. (1997b).

Hemispheric specialization for global and local processing: The effect of stimulus category. Proceedings

of the Royal Society of London Brain and Biological Sciences, 264, 487–494.

Gum, T., 1997. PsychLab. VI.0-103.2.

Halligan, P. W., & Marshall, J. C. (1994). Toward a principled explanation of unilateral neglect. Cognitive

Neuropsychology, 11, 167–206.

Heilman, K. M., & Van Den Abell, T. (1980). Right hemisphere dominance for attention: The mechanism

underlying hemispheric asymmetries of inattention (neglect). Neurology, 30, 327–330.

Heinze, H. J., Hinrichs, H., Scholz, M., Burchert, W., & Mangun, G. R. (1998). Neural mechanisms of

global and local processing: A combined PET and ERP study. Journal of Cognitive Neuroscience, 10,

485–498.

Hellige, J. B. (1980). Effects of perceptual quality and visual field of probe stimulus presentation on

memory search for letters. Journal of Experimental Psychology: Human Perception and Performance, 6,

639–651.

Hellige, J. B., Corwin, W. H., & Jonsson, J. E. (1984). Effects of perceptual quality on the processing of

human faces presented to the left and right cerebral hemispheres. Journal of Experimental Psychology:

Human Perception and Performance, 10, 90–107.

Hoffman, J. (1980). Interaction between global and local levels of a form. Journal of Experimental


Hood, D. C., & Finkelstein, M. A. (1986). Sensitivity to light. In K. Boff, L. Kaufman, & J. Thomas

(Eds.), Handbook of perception and human performance: Vol. 1 (pp. 5.1–5.66). New York: Wiley–

Interscience.

Hopkins, W. D. (1997). Hemispheric specialization for local and global processing of hierarchical visual

stimuli in chimpanzees (Pan troglodytes). Neuropsychologia, 35, 343–348.

H€uubner, R. (1997). The effect of spatial frequency on global precedence and hemispheric differences.

Perception & Psychophysics, 59, 187–201.

H€uubner, R. (1998). Hemispheric differences in global/local processing revealed by same-different

judgements. Visual Cognition, 5, 457–478.

Johannes, S., Wieringa, B. M., Matzke, M., & Munte, T. F. (1996). Hierarchical visual stimuli:

Electrophysiological evidence for separate left hemispheric global and local processing mechanisms in

humans. Neuroscience Letters, 210, 111–114.

Kahneman, D., & Norman, J. (1964). The time–intensity relation in visual perception as a function of

observer�s task. Journal of Experimental Psychology, 68, 215–220.

Kimchi, R., & Merhav, I. (1991). Hemispheric processing of global form, local form, and texture. Acta

Psychologica, 133–147.

Kinchla, R. A., Solis-Macias, V., & Hoffman, J. (1983). Attending to different levels of structure in a visual

image. Perception & Psychophysics, 33, 1–10.

Lamb, M. R., & Robertson, L. C. (1988). The processing of hierarchical stimuli: Effects of retinal locus,

locational uncertainty, and stimulus identity. Perception & Psychophysics, 44, 172–181.

Lamb, M. R., Robertson, L. C., & Knight, R. T. (1990). Component mechanisms underlying the

processing of hierarchically organized patterns: Inferences from patients with unilateral cortical

lesions. Journal of Experimental Psychology: Learning, Memory, and Cognition, 16, 471–483.

Lamb, M. R., & Yund, E. W. (1996). Spatial frequency and interference between global and local levels of

structure. Visual Cognition, 3, 193–219.

Loftus, G. R., & Ruthruff, E. (1994). A theory of visual information acquisition and visual memory with

special application to intensity-duration trade-offs. Journal of Experimental Psychology: Human

Perception and Performance, 20, 33–49.

Luna, D. (1993). Effects of exposure duration and eccentricity of global and local information on

processing dominance. European Journal of Cognitive Psychology, 5, 183–200.

MacWhinney, B. (1996). The PsyScope button box. Carnegie Mellon University.

Martin, M. (1979). Hemispheric specialization for local and global processing. Neuropsychologia, 17, 33–

40.

Martinez, A., Moses, P., Frank, L., Buxton, R., Wong, E., & Stiles, J. (1997). Hemispheric asymmetries in

global and local processing: Evidence from fMRI. Neuroreport, 8, 1685–1689.

Miller, J. (1981). Global precedence in attention and decision. Journal of Experimental Psychology: Human

Perception and Performance, 7, 1161–1174.

Navon, D. (1977). Forest before trees: The precedence of global features in visual perception. Cognitive

Psychology, 9, 353–383.

OptiCal (2002, Version 3.7d1) [Computer Software]. Lawrenceville, NJ: ColorVision, Inc.


Polich, J., & Aguilar, V. (1990). Hemispheric local/global processing revisited. Acta Psychologica, 74,

47–60.

Posner, M. I. (1980). Orienting of attention. Quarterly Journal of Experimental Psychology, 32, 3–25.

Posner, M. I., & Petersen, S. E. (1990). The attention system of the human brain. Annual Review of

Neuroscience, 13, 25–42.

Proverbio, A. M., Zani, A., Gazzaniga, M. S., & Mangun, G. R. (1994). ERP and RT signs of a rightward

bias for spatial orienting in a split-brain patient. Neuroreport, 5, 2457–2461.

Raab, D., & Fehrer, E. (1962). Supplementary report: The effect of stimulus duration and luminance on

visual reaction time. Journal of Experimental Psychology, 64, 326–327.

Rafal, R. T., & Robertson, L. (1995). The neurology of visual attention. In M. S. Gazzaniga (Ed.), The

cognitive neurosciences (pp. 625–648). Cambridge, MA: MIT Press.

Regan, D. (2000). Human perception of objects. Sunderland, MA: Sinauer Associates.

Robertson, L. C., Lamb, M. R., & Knight, R. T. (1988). Effects of lesions of temporal–parietal junction on

perceptual and attentional processing in humans. Journal of Neuroscience, 8, 3757–3769.

Robertson, L. C., Lamb, M. R., & Zaidel, E. (1993). Interhemispheric relations in processing hierarchical

patterns: Evidence from normal and commissurotomized subjects. Neuropsychology, 7, 325–342.

Roy, E. A., Reuter-Lorenz, P., Roy, L. G., Copland, S., & Moscovitch, M. (1987). Unilateral attention

deficits and hemispheric asymmetries in the control of attention. In M. Jeannerod (Ed.), Neurophys-

iological and neuropsychological aspects of spatial neglect (pp. 25–39). North Holland: Elsevier.

Sergent, J. (1982). The cerebral balance of power: Confrontation or cooperation? Journal of Experimental


Van Kleeck, M. H. (1989). Hemispheric differences in global versus local processing of hierarchical visual

stimuli by normal subjects: New data and a meta-analysis of previous studies. Neuropsychologia, 27,

1165–1178.

Verfaellie, M., Bowers, D., & Heilman, K. M. (1988). Hemispheric asymmetries in mediating intention,

but not selective attention. Neuropsychologia, 26, 521–531.

Versace, R., & Tiberghien, G. (1988). Sensitivity of cerebral hemispheres to the local and global

components of verbal and non-verbal stimuli. Cahiers de Psychologic Cognitive, 8, 125–137.

Yovel, G., Yovel, I., & Levy, J. (2001). Hemispheric asymmetries for global and local visual perception:

Effects of stimulus and task factors. Journal of Experimental Psychology: Human Perception and

Performance, 27, 1369–1385.


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