Race Categorization and Face Recognition Stages in the Processing of Laterally Displayed Unknown Faces

RACE CATEGORIZATION AND FACE RECOGNITION STAGES IN THE PROCESSING OF LATERALLY DISPLAYED UNKNOWN FACES Raymond Bmyer and Myriam Schweich (University of Louvain, Medical Department, Unite de Neuropsychologie Experimentale de l'Adulte)

The difficulty in the processing of faces when the stimuli do not issue from the same race as that of the subject is called the "race effect" (Brigham, 1986; Bruyer and Dussart, 1985; Lindsay and Wells, 1983; and Shepherd, 1981, for reviews). Recently, Bruyer and Dussart (1985) investigated the race effect in a recognition task involving African and Caucasian, laterally-displayed face. The "index of race effect" (IRE), essentially, was significant for the white subjects only and was limited to their right visual field (RVF). Thus, the left hemisphere seems to have difficulties in processing faces of another racial group: the right cerebral hemisphere was as efficient as the left and remained unaffected by the "race". According to Bruyer and Dussart, this result could be explained by, for example, the hypothesis that a familiarity effect was operative. The main purpose of the present study is to replicate this observation and to search for possible lateralized effects of familiarization to African .and Caucasian faces. In Exp. I, white subjects were enrolled in a task similar to that of Bruyer and Dussart but with a greater number of trials within each stimuli set: in each condition three successive blocks of 48 trials were administered and analyzed. Bruyer and Dussart used a single block of 64 trials. The right-sided race effect was expected to be more important and/ or more lateralized at the beginning than at the end of the experimental session. In the study of Bruyer and Dussart (1985) as well as in the present first experiment, stimuli were blocked as concerns the race: one condition concerned white faces, another black ones. It was assumed that the subjects did not make any "racial decision", and that the recognition process was directly activated. Thus, in Exp. II, black and white faces were randomly intermixed. Therefore, it was assumed that the subjects had to make a two-stage operation: the racial decision, then the recognition. We were unable to predict with confidence the kind of main effect of this change of experiment. Indeed, on the one hand, the need to perform Cortex (1987) 23, 415-429

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two successive operations could increase the difficulty, which would impair the efficiency. However, it could also facilitate the decision, given that "race" can be easily detected and that the recognition that follows would then be facilitated (the number of faces within each race being lower than in Exp. I). Therefore, we have compared mainly the two experiments by studying the IREs and lateral differences. A similar pattern of asymmetry concerning the IRE in both experiments could indicate that a racial decision was unavoidable and automatically triggered even when unnecessary (Exp. I). Conversely, any change in this pattern could reasonably be considered due to the racial decision. In both cases, however, it remained possible that the racial decision per se was lateralized. To clarify the interpretation, the subjects enrolled for Exp. II were enrolled in another experiment, a simple racial decision task. According to recent models (Ellis, 1983, 1986; Hay and Young, 1982), like gender categorization, racial classification would take place relatively early in the processing and before the decision of familiarity. In addition, racial (or gender) categorization would closely follow the facial decision operation. As concerns this facial decision, it seems that both hemispheres are able to manage the task and that asymmetries appear during the next, representational step (Hay, 1981 ; Young, Hay and McWeeny, 1985). As concerns gender categorization, it has been shown that such a task is faster than any recognition task and performed well by each hemisphere provided that stimuli are not experimentally degraded and that individual characteristics of the subjects are considered (Jones, 1979, 1980). This applies for unknown (Hellige and Jonsson, 1985; Hellige, Corwin and Jonsson, 1984; Jones, 1979, 1980; Sergent, 1982a), familiar (Sergent, 1985), as well as for famous faces (Marzi, Tassinari, Tressoldi, Barry and Grabowska, 1985). In short, we would like both to dissociate the recognition from the racial decision stages as responsible for the lateralization of the race effect reported by Bruyer and Dussart (1985), and to examine the role of familiarity on this phenomenon. EXPERIMENT I

The first experiment was essentially the same as that of Bruyer and Dussart (1985) with slight modifications in order to try to identify a familiarity effect to explain the lateralization of the race effect. Materials and Methods

The experiment was conducted with 16 naive, right-handed (self-report) female subjects with normal or corrected visual acuity, with a non-inverted hand

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position for writing, and no left-handed near relatives. The mean age was 22.69 years; SD = 1.93. Only white, Belgian subjects were enrolled. In addition, we selected those who had not been familiarized with the "other race": none had lived in Africa, and none had black people among her five best friends. The stimuli were those used by Bruyer and Dussart (1985). Within each stimulus race (Caucasian vs. African), eight kinds of slides were prepared. There were four neutral male full-faces, each displayed in the left (L VF) or right visual field (RVF), under the normal or mirror version. The size of the faces was 4 deg of angle of the visual field and faces were centered 4 deg left or right of the central fixation point. The slides were back-projected for 180 msec. A distractor face of the same ethnic group was systematically simultaneously displayed in the opposite field, with an arrowhead at fixation pointing towards the stimulus. Two distractors were randomly associated in the various occurrences of stimuli; the dis tractors were never used as targets. Each subject was submitted to two experimental conditions according to the stimulus, race in a balanced design. In both conditions, after preliminary trials for training, the subject was asked to depress the left button with the left index finger for two stimuli, the right (right index) for the other two. The button assignment was balanced across subjects. Each condition was introduced with 16 preliminary unanalyzed trials and then three blocks of 48 trials followed: in each block, each face (or its mirror image) appeared six times in each field, in a random sequence. The dependent measures were the proportions of errors (out of 24) and the reaction time of the correct responses (RT) by visual field, block, and stimulus' race. In addition, an IRE was computed with the two measures, by combining the scores on the two kinds of stimuli using the formula (other race - same race)/ (other race + same race); the IRE was therefore a number between -1 and + 1 with 0 indicating a lack of race effect. The results have generally been submitted to analyses of variance (ANOVAs), and the significant effects were then studied by the Newman-Keuls test (p<0.05).

Results

Table I displays the mean proportion of errors (out of 24) and the mean RTs in function of the block, visual field, and white vs. black faces, as well as the combined IREs. These results have been analyzed together with those of Exp. II (below). EXPERIMENT

II

The goal of this experiment is to engage the subjects in a two-stage decision task by inserting a preliminary "racial decision" stage before the recognition per se. Differences in the patterns of results between Exp. I and Exp. II would be due to this additional stage, which will be studied in isolation in Exp. IV. The lack of any difference between Exp. I and II, conversely, would suggest that a "racial decision" stage, although not

Block Left 1134 (.068) 1441 (.245) .1096 Right 1149 (.078) 1412 (.255) .1004

1

TABLE II

Block Left 1003 (.052) 1281 (.229) .1160 Right 1046 (.039) 1288 (.216) .0990

2

Block 3 Left Right 941 (.031) 926 (.031) 1243 (.185) 1233 (.151) .1243 .1278

IREs (RT)

White faces Black faces

Visual field:

Left 1115 (.094) 1342 (.198) .0800

Right 1238 (.089) 1569 (.234) .1066

Block 1

Left 957 (.036) 1138 (.089) .0790

Right 1146 (.031) 1193 (.182) .0590

Block 2

Left 874 (.021) 984 (.062) .0540

Right 868 (.010) 1180 (.104) .1443

Block 3

Mean Correct RTs (msec), Proportions of Errors out of 12 (between Parentheses) of Exp. II, and the Corresponding IREs. Means of 16 Subjects

IREs (RT)

Visual field: White faces Black faces

Mean correct RTs (msec), Proportions of Errors out of 24 (between Parentheses) of Exp. I, and the Corresponding IREs. Means of 16 Subjects

TABLE I

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necessary, was already at work in Exp I. Finally, it could be that both experiments differ only as a general main effect, which would indicate that the inserted task either facilitates or impairs the global process. Materials and Methods

Another series of 16 female subjects was enrolled, with identical criteria as for Exp. I. The mean age was 22.44 years; SD = 1.17. The stimuli were the same as those of Exp. I. However, black and white faces were randomly intermixed and the subjects had to recognize one .black and one white face by depressing a given button, and the other black and the other white face by depressing the other button. Thus, the initial material for preliminary learning was a set of two white and two black faces. Consequently, 50% of the initial trials were maintained, to design a single experiment with three blocks of 48 trials plus 16 items for familiarization. The discarded trials were retained for Exp. IV. The procedure was identical to that of Exp. I, with only one condition. Therefore, the order of conditions was irrelevant.

Results

Table II displays the mean proportion of errors (out of 12) and RTs by experimental condition, as for Exp. I. Analysis of Exps. I and II Errors

Since mean error rates as low as I or 2% appeared in at least some cells ,of Tables I and II, it was doubtfull that homogeneity of variances applied. Therefore, ANOVA has not been performed on errors, and the IREs have not been derived and analyzed. We can observe, at a purely descriptive level: (a) an advantage of white over black faces in every experiment X field X block combination; (b) an improvement of accuracy with familiarization (blocks), for black faces only; (c) a superiority of Exp. II over Exp. I, for black faces only; and (d) an advantage of the LVF over the RVF, for black faces only, which resulted more from Exp. II than from Exp. I. The combination of observations (c) and (d) would suggest an higher race effect in the RVF than in the LVF, especially during Exp. I. RTs

The experiment X field X race X block ANOVA on RTs revealed three significant main effects and one significant first-order interaction. Correct responses were faster to white (1033 msec) than black stimuli

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Fig. I - The experiment

X field significant interaction

RT(msec)

for the RTs in Exps. I and

Exp. II Exp. I

1200

/I.

1100

1000

1'" Left field

Right field

(1275: F= 36.4; dJ. = 1, 30; p< <0.001), and to stimuli displayed in the LVF (1119 msec) than to those shown in the RVF (1189: F= 6.1; d.f. = 1 , 30; p<0.025); the block significant main effect (F= 30.33; dJ. = 2,60; p< <0.001) evidenced that all the differences were significant among the three stages of the experimental session (1300 vs. 1132 vs. 1031 msec). The significant experiment X field interaction (F= 4.43; dJ. = 1, 30; p<0.05) is illustrated by Figure 1. The field effect was significant in Exp. II only, and an experiment effect appeared in the LVF only. The IREs derived from the RTs were analyzed by an experiment X field X block ANOVA. A significant, first-order, experiment X field interaction appeared (F= 4.64; dJ.= 1,30; p<0.05: Figure 2). The IRE of the LVF stimuli during Exp. II significantly differed from the other three, with no difference among these three. The sole other effect was a tendency toward an experiment X block interaction (F= 2.68; dJ. = 2, 60; p
Race categorization and face recognition

Fig. 2 -

The experiment -

X field significant interaction

for the IREs derived from RTs in Exps. I and /I.

421

IRE .12 .11

Exp.l Exp . l1

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.07 1" Left

field

Right field

Discussion We note first that even if statistical analyses of accuracy were not allowed, the two dependent measures agreed in their interpretative meaning, so no speed-accuracy tradeoff can be suspected. Second, if we consider the main effects, the results were, to a large extent, as expected: our white subjects processed white stimuli better than black; the recognition of faces was easier in the LVF than in the RVF; and the performance improved from the first through the third block of trials. - A first purpose of the present study was to test the familiarity interpretation of the laterality of the race effect found by Bruyer and Dussart (1985). In our Exp. I, which was the same as that made by Bruyer and Dussart except in length, and in-Exp. II also, we noted that advantage of white over black stimuli was observed within each block, and that the block effect was limited to the black faces in errors (but observed for black and white faces in RTs). More importantly, there was no sign of lateralization of this race X block interaction, no block X field interaction, and all the IREs of Exp. I differed significantly from zero. Thus, with a lengthened experiment, the signs of lateralized IRE disappeared. An evidence favoring our hypothesis could be found in the decreasing difference of accuracy between white and black stimuli from the beginning up to the end of the experimental session. Nevertheless, it is a weak argument, given the lack of interactions with the visual field. Therefore,

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there are discrepancies between our first experiment and the results reported bu Bruyer and Dussart as well as, evidently, no sign of reduction of the lateralization of IREs with practice. Moreover, no sign of lateralized practice effect appeared in our second, more similar to daily life conditions, experiment. As a transition to the second point of this Discussion, we note, in spite of the preceding comments, a locus of agreement between the present results and those of Bruyer and Dussart (1985). The descriptive analysis of accuracy suggested an higher race effect in the RVF that in the LVF, a phenomenon that was precisely obtained in the previous study. In addition, this race-by-field "interaction" seems to be larger in Exp. I (than in Exp. II), i.e., in the condition that was the most similar to that of Bruyer and Dussart (1985). So, the current data tend to replicate the previous ones. In addition, we note that this lateralization of the race effect was very more slight than in the previous study, which could suggest that it was at least in part due to familiarization (in the present study the experimental session was lengthened). The other purpose of this study was the search for lateralized differences between Exp. I and Exp. II. We recall that in Exp. I the subjects had to recognize faces within a predefined set of uniracial stimuli, while in Exp. II the recognition necessarily followed an early racial decision operation. There appeared a clear LVF superiority in Exp. II with no lateral difference in Exp. I: this was observed for errors and for RTs, as well as in the study of the IREs derived from the RTs. In addition, the examination of errors reveals that this LVF advantage in Exp. II was only due to the black stimuli. This last observation, therefore, qualified the r~ce X field descriptive interaction evidencing a LVF superiority for black faces: indeed, this effect was only present in Exp. II. Thus, in Exp. II, stimuli (especially black) were better recognized in the LVF than in the right, and the race effect was larger in the RVF than in the left. Moreover, the experiment effect was limited to the LVF for each dependent measure and the derived IREs. Since this effect systematically favored Exp. II, it therefore appeared that the addition of an early, racial-decision task facilitated the processing but in the LVF only. However, it was possible that the lateralization observed in Exp. II but not in Exp. I was not due to the recognition stage per se. Indeed, the preliminary race classification could be lateralized (better performed in the LVF than in the right), this asymmetry being then transferred to the subsequent stages (for this notion of transmitted asymmetry see Moscovitch, 1979). Experiment IV was planned to test this possibility. Before to start Exp. IV, however, an additional control was needed). lWe thank an anonymous reviewer who suggested this experiment.

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Exp. II was better performed than Exp. I, for faces shown in the LVF. This could agree with Sergent and Bindra's (1981) considerations about the possible lateralized effect of task difficulty. In Exp. II, provided the race categorization has been correctly performed (which will be examined in Exp. IV), the subject had to discriminate between two faces only (vs. four faces in Exp. I). Therefore, it could be that this reduction in task requirements had induced the LVF superiority in Exp. II. This hypothesis was empirically studied in Exp. III. EXPERIMENT III

Rationale and Methods

Exp. III has been designed in combining the procedure of Exps. I and II. Like in Exp. I, the recognition stage without preliminary race classification operation has been tested in Exp. III. However, like in Exp. II, the subjects of Exp. III had to discriminate between two faces only, within each kind of stimuli (black, white). A new series of 24 female subjects was enrolled, with identical criteria as for Exps. I and II (mean age = 22.54 years; SD= 1.14). Exp. III was identical to Exp I, with some modifications. Within each racial group of stimuli, the six possible pairs of faces have been used and the subjects had to depress the left or the right button according to the single laterally displayed face. The button assignment, the used pair face and the order of conditions (whites first vs. blacks first) were balanced across subjects, with one subjects in each of the 2 X 6 X 2 combinations.

Results

Errors were rare (about 2.5%) and not studied. The correct RTs have been submitted to the race X field X block ANOVA. It appeared a tendency towards a practice effect (F = 2.63; d.f. = 2,46; 0.05
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RVF than in the LVF (.0809 and .0905: F=3.l2; dJ.=I, 46; 0.1 >p>0.05). Discussion

The lateral differences recorded in Exp. II (with no asymmetry in Exp. I) were reproduced here without any early race decision. Therefore, there are reasons to think that differences between Exp. I and II were more related with the within-race difficulty than with the need for an early cognitive process of classification. This early operation alone will finally be studied in Exp. IV. EXPERIMENT IV

Rationale and Methods

In order to clarify the possible effect of a preliminary race classification, this task alone has been required from the subjects of Exp. II. The material of Exp. I not retained for Exp. II was used in Exp. IV. The procedure was identical, but the subjects had to categorize the faces as black vs. white by using the pushbuttons. The button assignment was balanced across subjects, as was the order of experiments (II vs. IV). In Exp. IV, the distractors displayed in the contralateral field were removed, since they were systematically of the same race as that of the target.

Results and Analysis

Errors were rare (1.3% of the responses), so the fixed, race X field X block ANOVA was not performed due to the floor-effects. For the same reason, IREs were not computed, analyzed in a field X block ANOVA or tested against zero. The RTs are shown in Table III; they were submitted to the race X field X block ANOVA. The sole significant result was a practice effect (F = 5.39; dJ. = 2,30; p
As expected, the racial decision task was easier (Exp. I: 13% errors, Exp. II: 9.5%, Exp. III: 2.5%, Exp. IV: 1.3%) and faster than the previous

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TABLE III

Mean Correct RTs (msec) and Their Corresponding IREs for Exp. IV Means of 16 Subjects

Visual field White faces Black faces IREs

Block 1 Left Right 639 669 645 653 -.0028 -.0079

Block 2 Left Right 621 623 618 589 -.0004 -.0171

Block 3 Left Right 594 616 621 605 -.0202 -.0090

ones (about 1175, 1130,721, and 625 msec for Exps. I, II, III, and IV, respectively). This observation supports the intuitive notion that race classification is an early stage in the processing, precedes the recognition stage, and can therefore be applied to both known and unknown faces. Similar considerations were suggested by recent models of face recognition (e.g. Ellis, 1983; Hay and Young, 1982) and have already been found in studies dealing with male/ female classification of known and unknown faces (e.g. Marzi et al., 1985; Sergent, 1985). No significant IRE emerged with this task, which is not surprising, given the race effect has usually been observed in recognition tasks and, in some cases, in discrimination tasks (Sherped, 1981, for a review). There was no reason, a priori, to suppose that white and black stimuli would differ in a task like the one used here. Finally, we noted a significant practice effect, but no sign of lateralization. The race categorization in the LVF was as fast as in the RVF. This could again support the notion that such a decision is a preliminary one, and not subject to asymmetrical processing (for sex categorization and similar results, see Hellige and Jonsson, 1985; Marzi et al., 1985; Sergent, 1985). More importantly, together with the results of Exp. III, it indicates that the results of Exps. I and II cannot be interpreted by an asymmetry in the early operations that would then be transferred to the subsequent stages. GENERAL DISCUSSION

In Bruyer and Dussart's study (1985), there was no sign of asymmetry of performance in the recognition of black and white faces, but the IRE derived from the RTs was significant in the RVF only. The authors hypothesized a familiarization effect to account for this observation. In order to test this hypothesis, we designed an experiment that replicated that of Bruyer and Dussart but with more trials (a single block of 64 trials vs. three blocks of 48 items). We replicated the lack of asymmetry of

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performance. In addition, the race effect was observed in each block of trials but the IRE remained significant from the beginning to the end of the experimental session, with no sign of lateralization; more precisely, it was significant in both visual fields. Finally, a familiarization effect appeared in both fields, which tended to be more important for black than for white stimuli. Therefore, we essentially reproduced the observations by Bruyer and Dussart, the race-effect now being observed in each hemifield. This result could be considered as not supporting the familiarization hypothesis. However, the interpretation of a lack of effect is always hazardous. In particular, it could be that various kinds of familiarity must be distinguished (as suggested elsewhere: Bruyer, Rectem and Dupuis, 1986). Bruyer and Dussart (1985) considered familiarization as the degree of daily-life exposure to faces of the other race. In support of this conception, they did not find signs of lateralization of the IREs in their black subjects who lived in Belgium and, therefore, had been "familiarized" with white faces (while their white subjects, like ours, had not been familiarized with blacks, i.e., they had no black friends and had not stayed in Africa). In our first experiment, we were probably dealing with another kind of familiarization, namely "experimental familiarization", i.e. the effect of seing a small set of previously unknown faces several times. These differences in the meaning of the "familiarity" could explain the empirical data. Experiments are needed in which the other kind of familiarity would be tested: it would be useful to enroll subjects with various degrees of "daily-life familiarity" with black faces, in order to study the correlations between the IREs and the level of familiarity, or to compare a group of familiarized to a group of unfamiliarized subjects. In our first experiment, as in the study by Bruyer and Dussart (1985), the trials were blocked as regards the race of the stimuli. Consequently, the "racial decision" stage was not needed, and the subjects were engaged in the recognition process only. In Exp. II, as in daily life conditions, black and white faces were mixed so that the subj ects were requested to perform a two-stage process: a racial classification operation and then the recognition processing. This time an advantage of the LVF appeared (especially for black faces), the IRE was higher in the right than in the LVF (as in the study by Bruyer and Dussart), and the IREs decreased from the first to the third block in the LVF only. This last observation runs counter to the familiarization hypothesis, which predicted a reduction of the IRE with practice, and reinforces the intuitive notion that another kind of familiarity should have been examined. However, this observation, together with the asymmetry of IRE, supports the previous study in that the left hemisphere could be less adapted to process unusual stimuli. It could be that the right brain is particularly involved in the processing of tasks for which no automatized

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operators are available -amI that the left intervenes with well-established routines, as suggested by Goldberg and Costa (1981). In addition, the "classic" LVF advantage for face recognition emerged in this experiment for a task needing a previous racial decision. But this asymmetry cannot be attributed to the transmission of an asymmetry from this early stage (Moscovith, 1979), since Exp. IV did not reveal any sign of lateralization. In addition, Exp. II was easier and faster than Exp. I for stimuli displayed in the LVF only. This result could be linked to the considerations of Sergent and Bindra (1981). Indeed, once the racial decision has been accomplished - and the results of Exp. IV indicate that this operation is made rapidly and with few errors - the subjects had only to discriminate among two faces inside the identified racial group, an operation that is classically better made in the left than in the RVF, at least with photographed, easily discriminable faces. Thus, the differences of laterality between Exp. I (no asymmetry) and Exp. II (LVF advantage) can be attributed to the reduction of the difficulty of the task: within a given racial group of stimuli, the subject had to discriminate between four faces in Exp. I, but between two in Exp. II. This argument is strongly strengthened by the results of Exp. III. In this last condition, as in Exp. II, the LVF advantage emerged while no early race decision was needed. Therefore, by combining this observation with the results of Exp. IV, it becomes obvious that the laterality effect in Exp. II (together with the lack of asymmetry in Exp. I) resulted more from the "within race" reduction of the task difficulty, than from the early racial decision operation. A last comment will concern the LVF superiority that was especially due to the black stimuli. This observation could be linked with the considerations of Sergent (1982b, 1983) who suggests that the right hemitspheric competence improves (relatively to that of the left) when the luminance of the material is reduced: obviously, our black faces were naturally less luminous than the white. However, there are three empirical arguments that run against such a simple, unifactorial interpretation. First, this hemifield X luminance interaction is usually evidenced with RTs, while we noted it in accurancy, not RTs. Second, this LVF advantage for black stimuli was observed in Exp. II only, yet the very same material was used in Exp. I. However, this phenomenon was more expected in Exp. II since the subjects had first to make an early racial categorization that can be considered as a luminance discrimination task. But the fourth experimental result deserves this interpretation: indeed, when the racial decision alone was examined (Exp. IV), there was no sign of race X field interaction and no sign of asymmetry. We conclude that we have examined a two-step process of face recognition in which each step, examined separately, is not lateralized but in

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which the combination reveals a right hemisphere superiority (and a smaller race effects, with some familiarization effect, within this right hemisphere). Therefore, it might be that some intermediate cognitive operations appeared between the racial categorization and the recognition, that were responsible for the laterality effects and that remain to be identified. The large difference in speed of processing between Exp. II (1130 msec) and Exp. IV (625 msec) can be considered empirical evidence favoring the existence of some such unknown intermediate operations; nevertheless, this difference must not be overestimated since the subjects had to process the directional information furnished by the arrow at the fixation point only in Exp. II. However, some methodological qualifications are in order that invite us to experiment further. First, we recall the various notions of face familiarity. Second, we have indicated the passage from a discrimination between four (blocked) faces in Exp. I to the discrimination between two in Exp. II (provided the racial classification has been correct ely made). Third, we note that in Exps. II and IV the subjects could base the racial decision on a "simple" dark/light discrimination. Thus, experiments with Caucasian vs. Oriental faces could well be fruitful. ABSTRACT

Bruyer and Dussart (1985) have recently shown that the "race effect", i.e. the difficulty in recognizing faces issuing from an ethnic group different from that of the subject, is limited to the right visual field. They suspected familiarization to be responsible for this asymmetry. In Exp. I, we tested this hypothesis by repeating the experiment of Bruyer and Dussart with a greater number of trials. A sample of 16 subjects were given the task of recognizing black and white faces laterally displayed for 180 msec. No laterality effect appeared, and the race effect was observed to an equal degree in each hemifield at all stages of the experimental session. It could thus be that various kinds of familiarization must be distinguished. In Exp. II, with 16 new subjects, the black and white faces were mixed so that the subjects had first to perform racial categorization, then a recognition. This time, an advantage of the left field appeared, the race effect was larger in the right than in the left field, and the race effect decreased with familiarization in the left field only. Two complementary experiments with 24 and 16 subjects showed that this phenomenon was not explainable by laterality effects in the early racial decision operation, but well by a lateralized effect of tasks requirements. REFERENCES

BRIGHAM, J.e. The influence of race on face recognition. In H.D. Ellis, M.A. Jeeves, F. Newcombe and A.W. Young (Eds.), Aspects of Face Processing. Dordrecht: Nijhoff, 1986. BRUYER, R., and DUSSART, T. Lateral differences in the race effect in face recognition. International Journal of Neuroscience, 28: 61-72, 1985.

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