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Categorical habituation to male and female faces: Gender schematic processing in infancy
INFANT
BEHAVIOR
AND
DEVELOPMENT
16,
317-332
(1993)
Categorical Habituation to Male and Female Faces: Gender Schematic Processing in Infancy MARY DRIVER LEINBACH University
of Oregon
BEVERLY I. FAGOT University
of Oregon and Oregon Social Learning
Center
Experiment 1 used an infant-controlled habituation procedure to assess 5-,7-, 9-, and 12-month-old infants’ ability to discriminate pictures of adult male and female faces categorically. The 9- and 12-month-old groups habituated to a series of male or female faces, generalized habituation to a new face of the same sex, and dishabituated when shown an apposite-sex face, showing discrimination of mole and female faces as separate categories. Use of an individual criterion lo determine which infants in each group showed this effect indicated that a proportion of infants ot each age were capable of making the discrimination categorically. In Experiment 2, the stimuli were altered so that different groups of 12-month-alds saw men and women pictured with unisex clothing, the women pictured with short hair, or the women pictured with short hair and both sexes pictured with unisex clothing. Decrements in categorical responding were significant only when bath hair and clothing were altered. Individually, a proportion of infants in each group demonstrated categorical recognition of mole and female faces despite the changes in the stimuli. These findings indicate that by 1 year of age, infants have incipient categories for men and women, and that these categories moy include information about sex-typical hair length and clothing styles.
gender-schematic infants
processing habituation
gender categories faces
Information-processing approaches to early cognitive development have led to schematic processing models of the acquisition of sex typing and stereotyping (Bern, 1981; Martin & Halverson, 1981). Children are now seen as perceiving and organizing the gender-relevant input that is available to them into conceptual structures that serve to guide their behavior and the subseThis research was supported by grants from the NICHD (1 ROI HD 17571) and the NSF (BSN-8615868) to B.I.F. We thank Margo Lane and Rachel R. W. Robertson for their assistance in conducting the study and two anonymous reviewers far comments and suggestions an an earlier version of this article. Portions of the research were presented at the International Conferences an Infant Studies, Los Angeles, CA, April 1986, and Montreal, Quebec, Canada, April 1990. Correspondence and requests far reprints should be sent to Mary D. Leinbach or Beverly Fagot, Department of Psychology, University of Oregon. Eugene. OR 97403.
317
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LEINBACH
AND FAGOT
quent processing of new material as well. This process leads to associative rather than piecemeal retention, so that related units of information will ultimately tend to be recognized and recalled together. These networks of associations are the basis of gender schemas that help the child organize and interpret new experiences and regulate gender-related behavior. The ability to perceive and respond to information categorically is of primary importance in building schemas. In order to construct any type of category system, the infant must surely need to be able to make the relevant discriminations and have the cognitive abilities necessary for organizing and chunking information. Infants at 10 months of age have shown that they can detect correlations among systematically varied attributes (Younger & Cohen, 1983), and when shown male faces whose features were varied systematically, they have demonstrated the ability to abstract a prototypical representation consisting of an average of the varying feature values (Strauss, 1979). Thus, it appears that detection of correlated attributes and the ability to form prototypes-cognitive processes that could be used to build a rudimentary gender schema-are available to infants less than 1 year old. Most pertinent to the building of a gender schema is the ability to respond to males and females as members of separate categories, a fundamental aspect of the structure, if not its cornerstone. Unfortunately, there is not.a great deal of information about early categorical discrimination of the sexes. Children’s ability to classify people as members of one sex or the other has most often been investigated by requiring the child to respond to labels such as man and woman, or boy and girl. Although these tasks demand only minimal verbal skill, they cannot be used with preverbal infants and thus cannot detect preverbal recognition of males and females as different kinds of people. However, infants do appear to respond differentially to men and women before acquiring the verbal skill necessary for labeling (Lewis & Brooks, 1974)) and some studies, usually addressed to questions of concept or category formation in general rather than the development of gender understanding, have shown gender-based discriminations in infancy (e.g., Cornell, 1974; Fagan, 1976). Habituation and visual preference studies have shown that infants well under 1 year of age can discriminate individual male and female faces (Cornell, 1974; Fagan, 1976). Fagan and Singer (1979) used a visual recognition task to demonstrate that 5- and 6-month-old infants are more likely to recognize whether or not a face is familiar on the basis of gender than on difference or similarity of facial structure. However, although we would expect discrimination of. male and female faces to underlie recognition that the individual faces belong to different categories, categorical knowledge is not shown by discrimination of single pairs of faces. According to Rosch’s (1978) criteria for the possession of categorical knowledge, an infant capable of categorization must treat discriminably different members of a category equivalently and must respond differently to a member of a contrasting category.
GENDER SCHEMATIC
PROCESSING
319
An extension of the habituation procedure, in which presentation of different examples in a category leads to a decrement in responding with generalization to new members of the familiar category and subsequent recovery of interest when the stimulus is changed (Horowitz, Paden, Bhana, & Self, 1972), can show categorical responding that meets Rosch’s (1978) criteria. Using this procedure, infants are presented with clearly discriminable instances of one category until a criterion for habituation (response decrement) is met. They are then tested for generalization of habituation to a new example of the now-familiar category and for dishabituation (recovery of interest as shown by increased responding) to a member of a contrast category. If the response decreases as the examples of the habituation category are presented, if it remains low for a new example of the familiar category, and if it then increases when an example of the contrast category is introduced, we can assume that the infant has lost interest in the familiar category as a whole and that the contrast stimulus is perceived as distinct from the familiar stimulus set. Two variations of this method have shown categorical responding to male and female voices in infants of 6 months and under. An infant-controlled visual habituation paradigm in which presentation of auditory stimuli is contingent upon the infant’s fixation of a visual stimulus can be used to detect habituation and recovery to auditory stimuli. Habituation to the auditory stimulus is shown by a decrement in fixation to the visual stimulus, and dishabituation or recovery of interest by an increase in visual fixation upon presentation new auditory stimulus (Horowitz, 1975). With this procedure, Miller (1983) found that 6-month-old infants who heard and habituated to male or female voices saying “hi” then detected a shift to voices of the opposite sex uttering the same word. Jusczyk, Pisoni, and Mullenix (1992) used a high-amplitude sucking procedure, in which presentation of voice stimuli was contingent upon the rate of sucking, to habituate infants to a series of male or female voices uttering a particular syllable. Following the habituation phase and a 2-min delay, the infants heard the same syllable produced by a series of voices of the opposite sex. At 2 months of age, infants readily acquired the sucking response, habituated (decreased the rate of sucking) to the first set of voices, and recovered interest (increased the rate of sucking) when voices of the opposite sex were presented. These studies show both early gender-based categorical responding and the usefulness of the habituation-recovery paradigm for investigating infants’ ability to categorize real-world stimuli. Presenting faces of one sex as the habituation and generalization stimuli and testing for recovery with a face of the opposite sex can demonstrate categorical discrimination of male and female faces, but this has not been done. Cohen and Strauss (1979) used an infant-controlled visual habituation procedure to habituate infants to a series of female faces in various orientations, then tested for recovery of interest with a familiar female face in a new
LEINBACH
320
AND FAGOT
orientation and an entirely new female face. At 30 weeks of age (but not at 18 or 24 weeks) infants generalized habituation to both test faces, suggesting that they were no longer interested in female faces, even new ones. Cohen and Strauss were not concerned with the development of gender categories as such, and did not include a male face as a novel stimulus. Although a male face might well have elicited recovery, their study did not demonstrate possession of the category of female faces as distinct from male faces: The infants could have been habituated to faces in general. This investigation used the infant-controlled visual habituation procedure, as did Cohen and Strauss (1979), to investigate infants’ discrimination of adult male and female faces as members of separate categories. Experiment 1 was designed to demonstrate that infants habituated to a series of faces of one sex would generalize habituation to a new face of the same sex but recover interest (dishabituate) when presented with a face of the opposite sex. Experiment 2 addressed the relative contributions of hair and clothing cues to infants’ categorical discrimination of male and female faces. EXPERIMENT
1
Method Subjects
Subjects were 80 infants, 20 at each of the ages of 5, 7, 9, and 12 months; males and females were represented equally at each age. The 5, 7-, and 9-month-olds were tested within 1 week of their monthly birth date, whereas the lZmonth-olds were within 12 months 2 4 weeks (M = 12.24 months). An additional 25 infants were lost to the study because of infant distress (12), mother interference (3), equipment failure (4), or scheduling error (6). These losses were distributed quite evenly across all ages and both sexes. Infants were from middle- and working-class families in the Eugene-Springfield, Oregon, area. Nearly all were Caucasian. Parents were recruited from a list maintained by the University of Oregon Psychology Department and were compensated for their participation. Stimulus
Materials
Two sets of slides were prepared from magazine and catalog pictures of attractive adult men and women highly stereotypic as to sex-typical dress and grooming. Each set of habituation stimuli consisted of 12 different same-sex faces. Two additional faces, one of each sex, were used as test stimuli. Pictures of both sexes differed, as do the actual men and women whom infants encounter, in facial orientation, coloring, hair length, expression, clothing style, and color, and, for men, in the presence or absence of facial hair. A black and white checkerboard pattern was presented as each subject’s first and last trial to determine that any decrement in fixation time was not due to fatigue or general loss of attention.
GENDER SCHEMATIC
PROCESSING
321
Procedure
An experimenter accompanied each infant-adult pair into the experimental room, instructed the adult to avoid cuing the infant or disrupting the procedure, and remained in the room throughout the session. Each infant was seated on the lap of his or her mother or other familiar adult, facing a white screen on which slides were back-projected from an adjacent room. Openings on either side of the screen’s 11.5cm square projection area permitted observation of the infant’s face from the projection room. Visual fixation times were recorded by an observer using a numeric keypad attached to an Apple IIe computer. The computer signaled the projectionist to change slides and calculated mean fixation times for each successive set of three trials. Each trial consisted of one unlimited look at the slide; when the infant looked away, the trial was ended and the screen became dark. A new slide was projected only when the observer signaled that the infant was looking away from the screen. Timing of each trial began with fixation on the slide and ended when the infant looked away. Each session began and ended with the checkerboard slide. Sex of subject and sex of stimulus were counterbalanced for each age group. Each infant was shown pictures from either the male or female series, repeating the series if necessary, until mean fixation time for three consecutive trials had declined to less than half of the highest three-trial mean in the infant’s own habituation trials. Three additional slides from the habituation series were shown to assure that habituation had occurred. A new face of the same sex was then presented to test for generalization of habituation, followed by an oppositesex face to assessrecovery. Observers were trained as the procedures were developed. For sessions conducted with two observers, the second observer used a hand-held datacollecting device (OS-3) to record fixation times. Pearson product-moment correlation coefficients were computed to assessagreement, with observers trained to a criterion of r > .90. New observers were trained to criterion with an experienced observer. Data Analyses
Group Comparisons. All analyses using group data were conducted with raw scores for variables involving fixation times converted to common logarithms in order to reduce variance and normalize distributions. Several preliminary analyses were carried out. To determine that any response decrement could not be attributed to fatigue, t tests were used to compare pre- and posttest checkerboard trials for each age group. To assess possible effects of age group, sex of subject, and sex of stimulus, three separate 4 x 2 x 2 (age group x sex of subject x sex of stimulus) analyses of variance (ANOVAS) were conducted on the mean number of trials to criterion, mean fixation times to the prehabituation stimuli, and recovery scores
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AND FAGOT
obtained by subtracting each infant’s mean log fixation time for the three posthabituation trials from the log fixation time for the recovery trial. The crucial prediction concerning recovery was tested separately for each age group. A priori one-tailed t tests were used to compare the mean log fixation time of the posthabituation trials to the mean log fixation times for the generalization (same-sex) test trial, and the recovery (opposite-sex) test trial. Recovery was assumed only for groups whose mean fixation time for the recovery trial was significantly greater than their mean fixation time for the posthabituation and generalization trials, with mean fixation time for the generalization trial not significantly greater than mean posthabituation trial fixation time. Individual Data. In order to evaluate recovery in individual infants, we adapted Reznick and Kagan’s (1983) criteria for dishabituation using singlestimulus presentations: fixation time to the novel stimulus exceeding mean fixation time for the last two habituation trials by 15% (weak criterion) or 25% (strong criterion) of the 7-s presentation time for each slide. As we used an infant-controlled procedure rather than a fixed presentation time for each stimulus slide, we credited infants with recovery of interest in response to the novel stimulus if fixation time to the recovery test trial exceeded mean fixation time for the three posthabituation trials by 20% of the mean fixation time for the infant’s longest three-trial block. Because some infants’ fixation times were quite variable, we added the stipulation that recovery fixation time must also exceed generalization test fixation time by at least 20% of mean fixation time for the longest three-trial bloc, and that generalization test fixation time could not exceed mean posthabituation fixation time by more than that amount. This is a fairly strong criterion, used in the attempt to avoid attributing dishabituation to infants whose recovery test fixation time was within the range of fixation times shown after habituation. Raw scores were used in these computations. Results involving individual data are reported as proportions of infants in age, sex, or stimulus groups showing recovery, with z (two-tailed) for the significance of differences in proportions used when appropriate. Predictions
All groups were expected to habituate to faces of one sex, generalize habituation to a new face of that sex, and show recovery when presented with a face of the opposite sex. Individually, at least some infants at each age were expected to demonstrate habituation to the series of male or female faces and recovery of interest in an opposite-sex face. The proportion of infants meeting the criterion for individual habituation and recovery was expected to increase in each succeedingly older age group. No effects due to sex of subject or sex of stimulus were predicted.
GENDER
SCHEMATIC
Results
323
PROCESSING
and Discussion
Data Analyses
Group Comparisons. Infants in all groups habituated as expected. Mean fixation times for the pre- and posttest checkerboard trials did not differ; thus, fatigue or general loss of interest could not account for decrements in fixation time across trials. The ANOVAs used to investigate differences due to age group, sex of subject, and sex of stimulus on mean fixation times for prehabituation trials or number of trials to habituation indicated no significant main effects and no interactions. The ANOVA investigating group differences in recovery, conducted on difference scores (log fixation time to recovery stimulus - mean log fixation time for the three posthabituation trials), yielded significant effects for age group, F(3, 64) = 6.38, p < .OOl, sex of subject, F(1, 64) = 5.44, p < .03, and sex of habituation stimulus, F(1, 64) = 6.52, p < .02. There were no significant interactions. A-posteriori comparisons (Fisher’s PLSD test) revealed that mean recovery scores for the 9- and 12month-olds (M = .171 and .257, SD = .200 and .053, respectively) were significantly greater than those for the 5- and 7-month groups (M = - .032 and - .029, SD = .115 and .015, respectively, p < .OS). Neither the two older nor the two younger groups differed significantly from each other. Boys’ mean recovery scores were greater than girls’ (M = .159 and .025, SD = .125 and .200, respectively), and presentation of a female face as recovery stimulus led to greater recovery scores (M = .165, SD = .lSS) than did presentation of a male face (M = .018, SD = .llO). Although mean recovery scores were expected to be greater for older groups, neither the greater recovery scores for boys, nor the apparently greater recovery of interest for a female face was expected. Means and standard deviations for posthabituation, generalization, and recovery trials for the four age groups are presented in Table 1. With regard to the major predictions of the study, only the two older
Mean
tog
Fixation
TABLE times for Posthobituotiol , Generolizotion, for 12-, 9-, 7-, and 5Month-Old lnfonts
ond
Recovery
Triols
Trials Posthobituotion Age
Group0
12 months 9 months 7 months 5 months
M WI 1.159 1.097 1.321 1.264
(0.215) (0.132) (0.221) (0.229)
Generalization M (SW 1.133 1.095 1.122 1.124
(0.274) (0.344) (0.358) (0.400)
Recovery M WI 1.4 16 1.267 1.292 1.232
(0.268) (0.332) (0.236) (0.344)
Note. Recovery wos attributed only to those groups whose meon fixation times for the recovery trial were significantly greoter thon those for the posthobituotion and generolizotion trials, and wos achieved only by the 9- and 12.month-old groups. On = 20 for each group.
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LEINBACH
AND
FAGOT
groups demonstrated recovery to the opposite-sex stimulus (mean fixation times for the recovery test trial significantly greater than mean fixation time for both the generalization trial and the three posthabituation trials, with mean fixation time for the generalization trial not significantly greater than for the posthabituation trials). At 9 and 12 months, the mean of the posthabituation trials did not differ from the mean for the generalization trial, but the recovery trial mean was significantly greater than the posthabituation trial mean (t = 2.37, p < .02, and t = 3.65, p < .OOl, respectively) and the generalization trial mean (t = 2.21, p < .02, 9 months, and I = 3.55, p < .002, 12 months). At 7 months, recovery trial fixation time was significantly greater than generalization trial fixation time, but not greater than the mean of the posthabituation trials. No significant recovery effects were found at 5 months. Mean log fixation times for the posthabituation, generalization, and recovery trials for each group are presented in Table 1. Individual Dafa. A proportion of infants at each age met the individual criteria for recovery: .45 at 12 months, .40 at 9 months, .lO at 7 months, and .20 at 5 months. The only significant differences among the proportions of infants showing recovery involved the 7-month-olds, who differed significantly from the 12- and 9-month-olds (z = 2.48, p < .Ol, and z = 2.19, p < .03, respectively). Compared with infants who failed to show recovery, infants who met the criteria for recovery to an opposite-sex face did not differ significantly in number of trials required to meet the criterion for habituation or in mean fixation times for the prehabituation trials. Figure 1 illustrates the proportion of infants showing recovery in each group. Although the sex-of-stimulus difference evident in the group data appeared as a trend in the individual data, the proportions of infants showing recovery when presented with a female face after habituation to a male face,
.
12
9
MONTHS Figure 1.
Proportion
of infonts
in each
age
7
5
OF AGE group
meeting
criteria
for recovery
GENDER SCHEMATIC
PROCESSING
325
38, was not significantly greater than the proportion showing recovery to a male face, .20 (z = 1.73, p > .08). The proportions showing recovery to male and female faces, respectively, were .50 and .40 at 12 months, .60 and .20 at 9 months, .lO and .lO at 7 months, and .30 and .lO at 5 months. The proportions of boys (.30) and girls (.28) showing recovery did not differ significantly. Experiment 1 showed that categorical discrimination of faces of either sex is within the capabilities of infants 1 year of age and younger. Although the group data showed significant recovery effects only at 9 and 12 months, the individual data indicate that categorical responding to male and female faces may be expected of some infants as young as 5 months of age. Why the 7-month-olds’ performance, as shown by the individual data, was poorer relative to the performance of the 9- and lZmonth-olds than that of the 5-month-olds is not clear. The group data indicated that boys were more likely than girls to respond to the change from a face of one sex to that of the other. However, we are reluctant to conclude that a reliable sex difference exists, as previous studies have shown inconsistent differences in boys’ and girls’ rates of habituation and recovery (Cohen, Gelber, & Lazar, 1971) and boys and girls were equally likely to meet the individual criteria for categorical recognition of male and female faces. The unexpected sex-of-stimulus effect has no ready explanation. Attempts to investigate the stability of this finding by using test pictures of a different man and woman to determine that the effect was not a function of the particular faces used were inconclusive. EXPERIMENT
2
According to gender-schema theory, early categorical recognition of men and women should begin to include detection of correlated attributes. These are the attributes that tend to distinguish males from females, but to co-occur within each sex (cf. Rosch, 1978), qualities and properties that are more typical of one sex than the other. Of the distinguishing information usually available to infants in this culture, hair length is considered particularly important (Itons-Peterson, 1988), but certain types of clothing are also more likely to be seen on one sex than the other. Because little is known concerning the cues infants use in discriminating men and women, Experiment 2 was designed to investigate lZmonth-old infants’ use of hair and clothing cues in categorical habituation to male and female faces. Method Subjects
Subjects were 60 infants tested within 2 weeks of their first birthday, three groups of 20 infants with 10 boys and 10 girls in each group. Data from 7
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LEINBACH
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FAGOT
additional infants, 4 boys and 3 girls, could not be used because of equipment failure (3), mother interference (l), or fussiness (3). The twenty 12-montholds from Experiment 1 served as a control group. Stimulus
Materials
Treatment of the four groups of subjects differed only in the crucial aspects of the stimulus materials shown. The control group (Experiment 1 infants) saw slides showing the faces of men or women as they appeared in magazine and catalogue photographs. The three altered-stimulus groups were shown different versions of the same slides. One group saw the slides with clothing altered so that men and women alike appeared to wear dark, turtle-necked shirts. Another group also saw the original faces, but with hair in the pictures of women carefully trimmed so that men’s and women’s hair appeared approximately the same length. The final group saw the same faces also, but with both clothing and hair altered as before. These changes are illustrated in Figure 2. Procedure
and Data Analyses
All procedures were the same as those used in Experiment 1. Sex of subject and sex of stimulus pictures were counterbalanced in all conditions. Data were analyzed for both group and individual effects as in Experiment 1. Predictions
We again expected that infants in all groups would habituate to the faces of either sex. If hair and clothing, rather than facial configuration as such, are
ORIGINAL
SHORT
UNISEX
HAIR
CLOTHES
SHORT AND UNISEX
Figure 2. Drawings clothing.
Actual
of original and altered stimuli were color slides.
stimulus
faces
illustrating
HAIR CLOTHES
the changes
made
to hair and
GENDER SCHEMATIC
PROCESSING
327
primary cues for infants’ discrimination of male and female faces, the groups seeing hair and/or clothing altered to make the sexes more similar should not recover interest in an opposite-sex face to the extent shown by the control group. Because hair length has been considered a major cue for recognition of the sexes (Itons-Peterson, 1988), we expected that shortening women’s hair would lead to a decrement in performance. We also expected that if the presence of sex-typed clothing bolsters infants’ ability to discriminate pictures of males and females, the group seeing pictures of men and women in unisex clothing would show some decrement relative to the control group, and that group seeing both hair and clothing altered to make the pictures of men and women more similar would be least likely to detect the change to a picture of the opposite sex. Results
and Discussion
Data Analyses
Group Comparisons. The infants in all groups habituated as expected. Neither the mean log fixation times for the pre- and posttest trials nor mean number of trials needed to reach the habituation criterion differed significantly for any group. A 4 x 2 x 2 (stimulus group x sex of infant x sex of stimulus) ANOVA using difference scores (mean log recovery fixation time - mean log posthabituation fixation time) indicated a significant main effect for group, F(3, 64) = 5.10, p < .004. A-posteriori comparisons (Fisher’s PLSD) indicated that the mean difference scores for the control group, the clothing-altered group, and the hair-altered group were significantly greater than the mean difference score for the group seeing both hair and clothing altered (M = .257, .lll, .066, and -.166, SD = .053, .160, .173, and .149, respectively, p < .05). No differences due to sex of subject or sex of stimulus pictures and no interactions were found. The a-priori t tests on group data, comparing mean log fixation times for the generalization and recovery trials to the mean of the posthabituation trials, showed significant recovery to the opposite-sex face for only the control group (the 12-month-old infants from Experiment 1). The group seeing only clothing altered were expected to detect the change to an opposite-sex face, but, although the infants generalized habituation to the new same-sex face, their mean fixation times for the recovery trial were not significantly greater than for the posthabituation and generalization trials (t = 1.23, p < .12; and t = 1.33, p < .ll). Means and standard deviations of the posthabituation, generalization, and recovery trials for the four stimulus conditions are presented in Table 2. Individual Data. The criteria for recovery in individual infants were the same as in Experiment 1. The proportion of control-group infants showing recovery (.45) did not differ significantly from that of the group seeing men
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LEINBACH
AND
TABLE Mean
tog
Fixation Times for Posthobituotion, for lnfonts in Control and Three
FAGOT
2 Generolizotion, Altered-Stimulus
ond Recovery Conditions
Trials
Triols
Condition0 Control Unisex
clothes
Short hoir Unisex clothes,
short
hair
Posthobituotion
Generolizotion
Recovery
M (SD)
M (SD)
M (SD)
1.159 1.281 1.157
(0.215) (0.236) (0.195)
1.133 1.252 1.237
(0.264)
1.223
(0.368)
1.384
(0.176)
1.304
(0.271)
1.218
(0.325)
Note. Recovery wos ottributed only to those groups whose trio1 were significantly greater thon those for the posthobituotion not achieved by any stimulus-oltered condition. On = 20 for each group.
(0.274) (0.277)
meon fixation times and generolizotion
1.4 16 (0.268) 1.392 (0.396)
for the recovery trials and wos
and women in unisex clothing (.40), or from that of the group seeing women with shortened hair and both sexes with unaltered clothing (.30). The proportion of infants seeing both hair and clothing altered (. 15) was significantly less than the proportion showing recovery in the control group (z = 2.07, p < .04). The proportions of infants showing recovery in each stimulus condition are presented in Figure 3. Whether considered separately from the control group or with the control group included, the groups seeing altered stimuli did not differ significantly in the proportions of infants showing recovery to faces of men and women, nor in the proportions of boys and girls showing recovery. To summarize, two of the three groups of infants who were shown altered stimulus pictures saw women with shortened hair, but one saw only clothing modified. Because the cue of longer hair was available, the latter group was expected to respond to the change to an opposite-sex face. As a group, these infants fell short of the criteria detecting the change from a face of one sex to that of the other, but they did not show significantly less attention to the opposite-sex face than did infants in the control group, who saw the original unaltered stimuli. Nor did significantly fewer of them meet the individual criteria for categorical recognition of male and female faces. The two remaining groups saw women with shortened hair, and one of these also saw men and women in unisex clothing. Although only the latter group differed significantly from the control group with regard to detecting the change to an opposite-sex face and in the proportion of infants showing categorical recognition of the change, the sequence of proportions of infants succeeding in each group is consistent with the presumed order of difficulty in discriminating male and female faces. That is, the poorest performance was given by infants for whom the sex-typical cues of both hair length and clothing were attenuated or removed, whereas the performance of infants seeing only
GENDER SCHEMATIC
UNISEX
CLOTHES
SHORT
HAIR
SHORT
HAIR
UNISEX
STIMULUS Figure 3. Proportion
329
PROCESSING
AND
CLOTHES
CONDITION
of infants in each stimulus condition
meeting criteria for recovery.
clothing altered was closest to that of the control group. Thus, it is possible that some of the infants were making use of hair length and sex-typed clothing either as jndividual or redundant cues in discriminating men and women. GENERAL
DISCUSSION
Together, the results of Experiments 1 and 2 indicate that categorical recognition of men and women is to be expected of 9- and lZmonth-old infants, is within the capabilities of some infants as young as 5 months of age, and can be demonstrated by some lZmonth-olds even when hair or clothing, or both, are altered to make the sexes appear more similar. These findings indicate that infants under 1 year of age have incipient categories for men and women, and that the categories may include information about sex-typical hair length and clothing styles. In light of Fagan and Singer’s (1979) finding that 5- to &month-old infants familiarized with a single male or female face will recognize even a highly similar opposite-sex face as novel, and Cohen and Strauss’s (1979) demonstration of categorical responding to female faces at 7 months, we were surprised that the 7-month-olds in Experiment 1 did not make a stronger showing. Fagan and Singer used a long familiarization presentation (two 30-s exposures to one face), which undoubtedly led to more thorough processing of the face. Because both the familiar and novel faces were presented for the test trials and displayed few differences other than gender, trying to process what discrepant information was available may have led the infants to search the novel face and, consequently, to indicate greater awareness of gender. The categorical habituation procedure we used requires the infant to extract the information that remains constant across a set of variable stimuli, a more difficult task. However, our procedure was virtually identical to that of Cohen and Strauss except for the presentation of an opposite-sex test trial; unless our
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AND FAGOT
7-month-olds were in some way atypical, it may be that many infants in both studies had habituated to faces in general, rather than to faces of one sex or the other. The possibility that hair length and sex-typical clothing can serve as cues for discriminating pictures of men and women does suggest caution in attributing conceptual categories, on the basis of habituation studies, to infants who may be responding to fairly superficial features. In responding to the limited information available in a photograph, the presence or absence of a specific cue may be sufficient to produce the habituation-recovery effect in some infants. Indeed, the presence of a salient feature may determine whether a stimulus will be discriminated on a perceptual or a conceptual basis (Kestenbaum & Nelson, 1990). We cannot say for certain that infants use hair and clothing cues to distinguish males and females, or whether, alternatively, they may be attending only to these cues. But even if some infants were to derive a category system comprised of long- and short-haired people, those categories would be differentially associated with males and females in our society. The infants in Experiment 2 who responded with renewed interest to an opposite-sex face were apparently observant enough to recognize the change from a face of one sex to that of the other even with hair and clothing made more similar, but we do not know what information about faces had become associated with either sex for them. Regardless of the nature of the developing categories, the demonstration of categorical perception of male and female faces, along with evidence that changes in hair and clothing style may influence gender recognition, indicate that perceptually available differences have begun to organize the processing of information along genderdimorphic lines. The greater recovery shown by infants who were habituated to a male face and tested with a female face raises the issue of preference which, although beyond the scope of this article, could be resolved using a standard visual preference paradigm. It is conceivable that young infants simply prefer to look at a female face. There could be other explanations, also. For example, Langlois, Ritter, Roggman, and Vaughn (1991) found that, with emotional cues held constant, 6-month-old infants preferred to look at attractive rather than unattractive adult faces of both sexes, but 7-month-olds in Nelson and Dolgin’s (1985) study generalized habituation to facial expressions of fear and happiness across male and female faces. Such findings suggest that young infants are sensitive to various aspects of faces, and that a number of variables, separately or together, could augment or reduce the salience of gender as a category of immediate interest. In this experiment, expression was varied intentionally to approximate conditions in ordinary life, and, although all of the stimulus faces were fairly attractive, we cannot be sure that subtle differences in expression or attractiveness did not contribute to the greater recovery of infants when the recovery stimulus was a female face. However, the same faces were used in Experiment 2, where no preference was evident.
GENDER SCHEMATIC PROCESSING
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Once infants have begun to incorporate sex-differentiated attributes into other information being encoded, the basis of a gender schema has been established. We should expect this to be the case. Given that the world of the infant is peopled with examples of both sexes and that gender serves as an organizing principle around which all societies build social categories, it would be surprising indeed if infants’ early categorization abilities failed to make use of so important a real-world category system as the distinction between female and male. REFERENCES Bern, S.L. (1981). Gender schema theory: A cognitive account of sex typing. Psychological Review,
88, 354-364.
Cohen, L.B., Gelber, E.R., & Lazar. M. (1971). Infant habituation and generalization to differing degrees of stimulus novelty. Journal of Experimental Child Psychology, II, 379-389. Cohen, L.B., & Strauss, M.S. (1979). Concept acquisition in the human infant. Child Development, 50, 419-424.
Cornell, E.H. (1974). Infants’ discrimination of faces following redundant presentations. Journal of Experimental Child Psychology, 18. 98-106. Fagan, J.F. (1976). Infants’ recognition of invariant features of faces. Child Development, 47, 627-638. Fagan, J.F., & Singer, L.T. (1979). The role of simple feature differences in infant recognition of faces. Infant Behavior and Development, 2, 39-46. Horowitz, F.D. (1975). Visual attention, auditory stimulation, and language discrimination in young infants. Monographs of the Society for Research in Child Development, 39(5-6, Serial No. 158). Horowitz, F.D., Paden, L., Bhana, K., & Self, P. (1972). An infant control procedure for Psychology, 7, 90. studying infant visual fixations. Developmental Itons-Peterson, M.J. (1988). Children’s concepts of gender. Not-wood, NJ: Ablex. Jusczyk, P.M., Pisoni, D.B., & Mullenix, J. (1992). Some consequences of stimulus variability on speech processing by two-month-old infants. Cognition, 43, 253-291. Kestenbaum, R., & Nelson, C.A. (1990). The recognition and categorization of upright and inverted emotional expressions by 7-month-old infants. Infant Behavior and Development, 13, 497-511. Langlois, J.H.. Ritter, J.M., Roggman, L.A., & Vaughn, L.S. (1991). Facial diversity and infant preferences for attractive faces. Developmental Psychology, 27, 79-84. Lewis, M., & Brooks, J. (1974). Self, other, and fear: Infants’ reactions to people. In M. Lewis & L. Rosenblum (Eds.), The origins of behavior: Vol. 2. The origins of fear. New York: Academic. Martin, C.L., & Halverson, C.F. (1981). A schematic processing model of sex typing and stereotyping in children. Child Development, 52, 1119-l 134. Miller, C.L. (1983). Developmental changes in male/female voice classification by infants. Infants
Behavior
and Development,
6, 313-330.
Nelson, C.A., & Dolgin, K.G. (1985). The generalized discrimination of facial expressions by seven-month-old infants. Child Development, 56, 5861. Reznick, J.S., & Kagan, J. (1983). Category detection in infancy. In L.P. Lipsitt (Ed.), Advances in infancy research (Vol. 2). Norwood, NJ: Ablex. Rosch, E. (1978). Principles of categorization. In E. Rosch & B.B. Lloyd (Eds.), Cognition and categorization. Hillsdale, NJ: Erlbaum.
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Strauss, M.S. (1979). Abstraction of prototypical information by adults and lo-month-old infants. Journal of Experimental Psychology: Human Learning and Memory, 5, 618-632. Younger, B.A., & Cohen, L.B. (1983). Infant perception of correlated attributes. Child Development,
54, 858-867.
7 July 1991; Revised 21 May 1992 W
BEHAVIOR
AND
DEVELOPMENT
16,
317-332
(1993)
Categorical Habituation to Male and Female Faces: Gender Schematic Processing in Infancy MARY DRIVER LEINBACH University
of Oregon
BEVERLY I. FAGOT University
of Oregon and Oregon Social Learning
Center
Experiment 1 used an infant-controlled habituation procedure to assess 5-,7-, 9-, and 12-month-old infants’ ability to discriminate pictures of adult male and female faces categorically. The 9- and 12-month-old groups habituated to a series of male or female faces, generalized habituation to a new face of the same sex, and dishabituated when shown an apposite-sex face, showing discrimination of mole and female faces as separate categories. Use of an individual criterion lo determine which infants in each group showed this effect indicated that a proportion of infants ot each age were capable of making the discrimination categorically. In Experiment 2, the stimuli were altered so that different groups of 12-month-alds saw men and women pictured with unisex clothing, the women pictured with short hair, or the women pictured with short hair and both sexes pictured with unisex clothing. Decrements in categorical responding were significant only when bath hair and clothing were altered. Individually, a proportion of infants in each group demonstrated categorical recognition of mole and female faces despite the changes in the stimuli. These findings indicate that by 1 year of age, infants have incipient categories for men and women, and that these categories moy include information about sex-typical hair length and clothing styles.
gender-schematic infants
processing habituation
gender categories faces
Information-processing approaches to early cognitive development have led to schematic processing models of the acquisition of sex typing and stereotyping (Bern, 1981; Martin & Halverson, 1981). Children are now seen as perceiving and organizing the gender-relevant input that is available to them into conceptual structures that serve to guide their behavior and the subseThis research was supported by grants from the NICHD (1 ROI HD 17571) and the NSF (BSN-8615868) to B.I.F. We thank Margo Lane and Rachel R. W. Robertson for their assistance in conducting the study and two anonymous reviewers far comments and suggestions an an earlier version of this article. Portions of the research were presented at the International Conferences an Infant Studies, Los Angeles, CA, April 1986, and Montreal, Quebec, Canada, April 1990. Correspondence and requests far reprints should be sent to Mary D. Leinbach or Beverly Fagot, Department of Psychology, University of Oregon. Eugene. OR 97403.
317
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LEINBACH
AND FAGOT
quent processing of new material as well. This process leads to associative rather than piecemeal retention, so that related units of information will ultimately tend to be recognized and recalled together. These networks of associations are the basis of gender schemas that help the child organize and interpret new experiences and regulate gender-related behavior. The ability to perceive and respond to information categorically is of primary importance in building schemas. In order to construct any type of category system, the infant must surely need to be able to make the relevant discriminations and have the cognitive abilities necessary for organizing and chunking information. Infants at 10 months of age have shown that they can detect correlations among systematically varied attributes (Younger & Cohen, 1983), and when shown male faces whose features were varied systematically, they have demonstrated the ability to abstract a prototypical representation consisting of an average of the varying feature values (Strauss, 1979). Thus, it appears that detection of correlated attributes and the ability to form prototypes-cognitive processes that could be used to build a rudimentary gender schema-are available to infants less than 1 year old. Most pertinent to the building of a gender schema is the ability to respond to males and females as members of separate categories, a fundamental aspect of the structure, if not its cornerstone. Unfortunately, there is not.a great deal of information about early categorical discrimination of the sexes. Children’s ability to classify people as members of one sex or the other has most often been investigated by requiring the child to respond to labels such as man and woman, or boy and girl. Although these tasks demand only minimal verbal skill, they cannot be used with preverbal infants and thus cannot detect preverbal recognition of males and females as different kinds of people. However, infants do appear to respond differentially to men and women before acquiring the verbal skill necessary for labeling (Lewis & Brooks, 1974)) and some studies, usually addressed to questions of concept or category formation in general rather than the development of gender understanding, have shown gender-based discriminations in infancy (e.g., Cornell, 1974; Fagan, 1976). Habituation and visual preference studies have shown that infants well under 1 year of age can discriminate individual male and female faces (Cornell, 1974; Fagan, 1976). Fagan and Singer (1979) used a visual recognition task to demonstrate that 5- and 6-month-old infants are more likely to recognize whether or not a face is familiar on the basis of gender than on difference or similarity of facial structure. However, although we would expect discrimination of. male and female faces to underlie recognition that the individual faces belong to different categories, categorical knowledge is not shown by discrimination of single pairs of faces. According to Rosch’s (1978) criteria for the possession of categorical knowledge, an infant capable of categorization must treat discriminably different members of a category equivalently and must respond differently to a member of a contrasting category.
GENDER SCHEMATIC
PROCESSING
319
An extension of the habituation procedure, in which presentation of different examples in a category leads to a decrement in responding with generalization to new members of the familiar category and subsequent recovery of interest when the stimulus is changed (Horowitz, Paden, Bhana, & Self, 1972), can show categorical responding that meets Rosch’s (1978) criteria. Using this procedure, infants are presented with clearly discriminable instances of one category until a criterion for habituation (response decrement) is met. They are then tested for generalization of habituation to a new example of the now-familiar category and for dishabituation (recovery of interest as shown by increased responding) to a member of a contrast category. If the response decreases as the examples of the habituation category are presented, if it remains low for a new example of the familiar category, and if it then increases when an example of the contrast category is introduced, we can assume that the infant has lost interest in the familiar category as a whole and that the contrast stimulus is perceived as distinct from the familiar stimulus set. Two variations of this method have shown categorical responding to male and female voices in infants of 6 months and under. An infant-controlled visual habituation paradigm in which presentation of auditory stimuli is contingent upon the infant’s fixation of a visual stimulus can be used to detect habituation and recovery to auditory stimuli. Habituation to the auditory stimulus is shown by a decrement in fixation to the visual stimulus, and dishabituation or recovery of interest by an increase in visual fixation upon presentation new auditory stimulus (Horowitz, 1975). With this procedure, Miller (1983) found that 6-month-old infants who heard and habituated to male or female voices saying “hi” then detected a shift to voices of the opposite sex uttering the same word. Jusczyk, Pisoni, and Mullenix (1992) used a high-amplitude sucking procedure, in which presentation of voice stimuli was contingent upon the rate of sucking, to habituate infants to a series of male or female voices uttering a particular syllable. Following the habituation phase and a 2-min delay, the infants heard the same syllable produced by a series of voices of the opposite sex. At 2 months of age, infants readily acquired the sucking response, habituated (decreased the rate of sucking) to the first set of voices, and recovered interest (increased the rate of sucking) when voices of the opposite sex were presented. These studies show both early gender-based categorical responding and the usefulness of the habituation-recovery paradigm for investigating infants’ ability to categorize real-world stimuli. Presenting faces of one sex as the habituation and generalization stimuli and testing for recovery with a face of the opposite sex can demonstrate categorical discrimination of male and female faces, but this has not been done. Cohen and Strauss (1979) used an infant-controlled visual habituation procedure to habituate infants to a series of female faces in various orientations, then tested for recovery of interest with a familiar female face in a new
LEINBACH
320
AND FAGOT
orientation and an entirely new female face. At 30 weeks of age (but not at 18 or 24 weeks) infants generalized habituation to both test faces, suggesting that they were no longer interested in female faces, even new ones. Cohen and Strauss were not concerned with the development of gender categories as such, and did not include a male face as a novel stimulus. Although a male face might well have elicited recovery, their study did not demonstrate possession of the category of female faces as distinct from male faces: The infants could have been habituated to faces in general. This investigation used the infant-controlled visual habituation procedure, as did Cohen and Strauss (1979), to investigate infants’ discrimination of adult male and female faces as members of separate categories. Experiment 1 was designed to demonstrate that infants habituated to a series of faces of one sex would generalize habituation to a new face of the same sex but recover interest (dishabituate) when presented with a face of the opposite sex. Experiment 2 addressed the relative contributions of hair and clothing cues to infants’ categorical discrimination of male and female faces. EXPERIMENT
1
Method Subjects
Subjects were 80 infants, 20 at each of the ages of 5, 7, 9, and 12 months; males and females were represented equally at each age. The 5, 7-, and 9-month-olds were tested within 1 week of their monthly birth date, whereas the lZmonth-olds were within 12 months 2 4 weeks (M = 12.24 months). An additional 25 infants were lost to the study because of infant distress (12), mother interference (3), equipment failure (4), or scheduling error (6). These losses were distributed quite evenly across all ages and both sexes. Infants were from middle- and working-class families in the Eugene-Springfield, Oregon, area. Nearly all were Caucasian. Parents were recruited from a list maintained by the University of Oregon Psychology Department and were compensated for their participation. Stimulus
Materials
Two sets of slides were prepared from magazine and catalog pictures of attractive adult men and women highly stereotypic as to sex-typical dress and grooming. Each set of habituation stimuli consisted of 12 different same-sex faces. Two additional faces, one of each sex, were used as test stimuli. Pictures of both sexes differed, as do the actual men and women whom infants encounter, in facial orientation, coloring, hair length, expression, clothing style, and color, and, for men, in the presence or absence of facial hair. A black and white checkerboard pattern was presented as each subject’s first and last trial to determine that any decrement in fixation time was not due to fatigue or general loss of attention.
GENDER SCHEMATIC
PROCESSING
321
Procedure
An experimenter accompanied each infant-adult pair into the experimental room, instructed the adult to avoid cuing the infant or disrupting the procedure, and remained in the room throughout the session. Each infant was seated on the lap of his or her mother or other familiar adult, facing a white screen on which slides were back-projected from an adjacent room. Openings on either side of the screen’s 11.5cm square projection area permitted observation of the infant’s face from the projection room. Visual fixation times were recorded by an observer using a numeric keypad attached to an Apple IIe computer. The computer signaled the projectionist to change slides and calculated mean fixation times for each successive set of three trials. Each trial consisted of one unlimited look at the slide; when the infant looked away, the trial was ended and the screen became dark. A new slide was projected only when the observer signaled that the infant was looking away from the screen. Timing of each trial began with fixation on the slide and ended when the infant looked away. Each session began and ended with the checkerboard slide. Sex of subject and sex of stimulus were counterbalanced for each age group. Each infant was shown pictures from either the male or female series, repeating the series if necessary, until mean fixation time for three consecutive trials had declined to less than half of the highest three-trial mean in the infant’s own habituation trials. Three additional slides from the habituation series were shown to assure that habituation had occurred. A new face of the same sex was then presented to test for generalization of habituation, followed by an oppositesex face to assessrecovery. Observers were trained as the procedures were developed. For sessions conducted with two observers, the second observer used a hand-held datacollecting device (OS-3) to record fixation times. Pearson product-moment correlation coefficients were computed to assessagreement, with observers trained to a criterion of r > .90. New observers were trained to criterion with an experienced observer. Data Analyses
Group Comparisons. All analyses using group data were conducted with raw scores for variables involving fixation times converted to common logarithms in order to reduce variance and normalize distributions. Several preliminary analyses were carried out. To determine that any response decrement could not be attributed to fatigue, t tests were used to compare pre- and posttest checkerboard trials for each age group. To assess possible effects of age group, sex of subject, and sex of stimulus, three separate 4 x 2 x 2 (age group x sex of subject x sex of stimulus) analyses of variance (ANOVAS) were conducted on the mean number of trials to criterion, mean fixation times to the prehabituation stimuli, and recovery scores
322
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AND FAGOT
obtained by subtracting each infant’s mean log fixation time for the three posthabituation trials from the log fixation time for the recovery trial. The crucial prediction concerning recovery was tested separately for each age group. A priori one-tailed t tests were used to compare the mean log fixation time of the posthabituation trials to the mean log fixation times for the generalization (same-sex) test trial, and the recovery (opposite-sex) test trial. Recovery was assumed only for groups whose mean fixation time for the recovery trial was significantly greater than their mean fixation time for the posthabituation and generalization trials, with mean fixation time for the generalization trial not significantly greater than mean posthabituation trial fixation time. Individual Data. In order to evaluate recovery in individual infants, we adapted Reznick and Kagan’s (1983) criteria for dishabituation using singlestimulus presentations: fixation time to the novel stimulus exceeding mean fixation time for the last two habituation trials by 15% (weak criterion) or 25% (strong criterion) of the 7-s presentation time for each slide. As we used an infant-controlled procedure rather than a fixed presentation time for each stimulus slide, we credited infants with recovery of interest in response to the novel stimulus if fixation time to the recovery test trial exceeded mean fixation time for the three posthabituation trials by 20% of the mean fixation time for the infant’s longest three-trial block. Because some infants’ fixation times were quite variable, we added the stipulation that recovery fixation time must also exceed generalization test fixation time by at least 20% of mean fixation time for the longest three-trial bloc, and that generalization test fixation time could not exceed mean posthabituation fixation time by more than that amount. This is a fairly strong criterion, used in the attempt to avoid attributing dishabituation to infants whose recovery test fixation time was within the range of fixation times shown after habituation. Raw scores were used in these computations. Results involving individual data are reported as proportions of infants in age, sex, or stimulus groups showing recovery, with z (two-tailed) for the significance of differences in proportions used when appropriate. Predictions
All groups were expected to habituate to faces of one sex, generalize habituation to a new face of that sex, and show recovery when presented with a face of the opposite sex. Individually, at least some infants at each age were expected to demonstrate habituation to the series of male or female faces and recovery of interest in an opposite-sex face. The proportion of infants meeting the criterion for individual habituation and recovery was expected to increase in each succeedingly older age group. No effects due to sex of subject or sex of stimulus were predicted.
GENDER
SCHEMATIC
Results
323
PROCESSING
and Discussion
Data Analyses
Group Comparisons. Infants in all groups habituated as expected. Mean fixation times for the pre- and posttest checkerboard trials did not differ; thus, fatigue or general loss of interest could not account for decrements in fixation time across trials. The ANOVAs used to investigate differences due to age group, sex of subject, and sex of stimulus on mean fixation times for prehabituation trials or number of trials to habituation indicated no significant main effects and no interactions. The ANOVA investigating group differences in recovery, conducted on difference scores (log fixation time to recovery stimulus - mean log fixation time for the three posthabituation trials), yielded significant effects for age group, F(3, 64) = 6.38, p < .OOl, sex of subject, F(1, 64) = 5.44, p < .03, and sex of habituation stimulus, F(1, 64) = 6.52, p < .02. There were no significant interactions. A-posteriori comparisons (Fisher’s PLSD test) revealed that mean recovery scores for the 9- and 12month-olds (M = .171 and .257, SD = .200 and .053, respectively) were significantly greater than those for the 5- and 7-month groups (M = - .032 and - .029, SD = .115 and .015, respectively, p < .OS). Neither the two older nor the two younger groups differed significantly from each other. Boys’ mean recovery scores were greater than girls’ (M = .159 and .025, SD = .125 and .200, respectively), and presentation of a female face as recovery stimulus led to greater recovery scores (M = .165, SD = .lSS) than did presentation of a male face (M = .018, SD = .llO). Although mean recovery scores were expected to be greater for older groups, neither the greater recovery scores for boys, nor the apparently greater recovery of interest for a female face was expected. Means and standard deviations for posthabituation, generalization, and recovery trials for the four age groups are presented in Table 1. With regard to the major predictions of the study, only the two older
Mean
tog
Fixation
TABLE times for Posthobituotiol , Generolizotion, for 12-, 9-, 7-, and 5Month-Old lnfonts
ond
Recovery
Triols
Trials Posthobituotion Age
Group0
12 months 9 months 7 months 5 months
M WI 1.159 1.097 1.321 1.264
(0.215) (0.132) (0.221) (0.229)
Generalization M (SW 1.133 1.095 1.122 1.124
(0.274) (0.344) (0.358) (0.400)
Recovery M WI 1.4 16 1.267 1.292 1.232
(0.268) (0.332) (0.236) (0.344)
Note. Recovery wos attributed only to those groups whose meon fixation times for the recovery trial were significantly greoter thon those for the posthobituotion and generolizotion trials, and wos achieved only by the 9- and 12.month-old groups. On = 20 for each group.
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FAGOT
groups demonstrated recovery to the opposite-sex stimulus (mean fixation times for the recovery test trial significantly greater than mean fixation time for both the generalization trial and the three posthabituation trials, with mean fixation time for the generalization trial not significantly greater than for the posthabituation trials). At 9 and 12 months, the mean of the posthabituation trials did not differ from the mean for the generalization trial, but the recovery trial mean was significantly greater than the posthabituation trial mean (t = 2.37, p < .02, and t = 3.65, p < .OOl, respectively) and the generalization trial mean (t = 2.21, p < .02, 9 months, and I = 3.55, p < .002, 12 months). At 7 months, recovery trial fixation time was significantly greater than generalization trial fixation time, but not greater than the mean of the posthabituation trials. No significant recovery effects were found at 5 months. Mean log fixation times for the posthabituation, generalization, and recovery trials for each group are presented in Table 1. Individual Dafa. A proportion of infants at each age met the individual criteria for recovery: .45 at 12 months, .40 at 9 months, .lO at 7 months, and .20 at 5 months. The only significant differences among the proportions of infants showing recovery involved the 7-month-olds, who differed significantly from the 12- and 9-month-olds (z = 2.48, p < .Ol, and z = 2.19, p < .03, respectively). Compared with infants who failed to show recovery, infants who met the criteria for recovery to an opposite-sex face did not differ significantly in number of trials required to meet the criterion for habituation or in mean fixation times for the prehabituation trials. Figure 1 illustrates the proportion of infants showing recovery in each group. Although the sex-of-stimulus difference evident in the group data appeared as a trend in the individual data, the proportions of infants showing recovery when presented with a female face after habituation to a male face,
.
12
9
MONTHS Figure 1.
Proportion
of infonts
in each
age
7
5
OF AGE group
meeting
criteria
for recovery
GENDER SCHEMATIC
PROCESSING
325
38, was not significantly greater than the proportion showing recovery to a male face, .20 (z = 1.73, p > .08). The proportions showing recovery to male and female faces, respectively, were .50 and .40 at 12 months, .60 and .20 at 9 months, .lO and .lO at 7 months, and .30 and .lO at 5 months. The proportions of boys (.30) and girls (.28) showing recovery did not differ significantly. Experiment 1 showed that categorical discrimination of faces of either sex is within the capabilities of infants 1 year of age and younger. Although the group data showed significant recovery effects only at 9 and 12 months, the individual data indicate that categorical responding to male and female faces may be expected of some infants as young as 5 months of age. Why the 7-month-olds’ performance, as shown by the individual data, was poorer relative to the performance of the 9- and lZmonth-olds than that of the 5-month-olds is not clear. The group data indicated that boys were more likely than girls to respond to the change from a face of one sex to that of the other. However, we are reluctant to conclude that a reliable sex difference exists, as previous studies have shown inconsistent differences in boys’ and girls’ rates of habituation and recovery (Cohen, Gelber, & Lazar, 1971) and boys and girls were equally likely to meet the individual criteria for categorical recognition of male and female faces. The unexpected sex-of-stimulus effect has no ready explanation. Attempts to investigate the stability of this finding by using test pictures of a different man and woman to determine that the effect was not a function of the particular faces used were inconclusive. EXPERIMENT
2
According to gender-schema theory, early categorical recognition of men and women should begin to include detection of correlated attributes. These are the attributes that tend to distinguish males from females, but to co-occur within each sex (cf. Rosch, 1978), qualities and properties that are more typical of one sex than the other. Of the distinguishing information usually available to infants in this culture, hair length is considered particularly important (Itons-Peterson, 1988), but certain types of clothing are also more likely to be seen on one sex than the other. Because little is known concerning the cues infants use in discriminating men and women, Experiment 2 was designed to investigate lZmonth-old infants’ use of hair and clothing cues in categorical habituation to male and female faces. Method Subjects
Subjects were 60 infants tested within 2 weeks of their first birthday, three groups of 20 infants with 10 boys and 10 girls in each group. Data from 7
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LEINBACH
AND
FAGOT
additional infants, 4 boys and 3 girls, could not be used because of equipment failure (3), mother interference (l), or fussiness (3). The twenty 12-montholds from Experiment 1 served as a control group. Stimulus
Materials
Treatment of the four groups of subjects differed only in the crucial aspects of the stimulus materials shown. The control group (Experiment 1 infants) saw slides showing the faces of men or women as they appeared in magazine and catalogue photographs. The three altered-stimulus groups were shown different versions of the same slides. One group saw the slides with clothing altered so that men and women alike appeared to wear dark, turtle-necked shirts. Another group also saw the original faces, but with hair in the pictures of women carefully trimmed so that men’s and women’s hair appeared approximately the same length. The final group saw the same faces also, but with both clothing and hair altered as before. These changes are illustrated in Figure 2. Procedure
and Data Analyses
All procedures were the same as those used in Experiment 1. Sex of subject and sex of stimulus pictures were counterbalanced in all conditions. Data were analyzed for both group and individual effects as in Experiment 1. Predictions
We again expected that infants in all groups would habituate to the faces of either sex. If hair and clothing, rather than facial configuration as such, are
ORIGINAL
SHORT
UNISEX
HAIR
CLOTHES
SHORT AND UNISEX
Figure 2. Drawings clothing.
Actual
of original and altered stimuli were color slides.
stimulus
faces
illustrating
HAIR CLOTHES
the changes
made
to hair and
GENDER SCHEMATIC
PROCESSING
327
primary cues for infants’ discrimination of male and female faces, the groups seeing hair and/or clothing altered to make the sexes more similar should not recover interest in an opposite-sex face to the extent shown by the control group. Because hair length has been considered a major cue for recognition of the sexes (Itons-Peterson, 1988), we expected that shortening women’s hair would lead to a decrement in performance. We also expected that if the presence of sex-typed clothing bolsters infants’ ability to discriminate pictures of males and females, the group seeing pictures of men and women in unisex clothing would show some decrement relative to the control group, and that group seeing both hair and clothing altered to make the pictures of men and women more similar would be least likely to detect the change to a picture of the opposite sex. Results
and Discussion
Data Analyses
Group Comparisons. The infants in all groups habituated as expected. Neither the mean log fixation times for the pre- and posttest trials nor mean number of trials needed to reach the habituation criterion differed significantly for any group. A 4 x 2 x 2 (stimulus group x sex of infant x sex of stimulus) ANOVA using difference scores (mean log recovery fixation time - mean log posthabituation fixation time) indicated a significant main effect for group, F(3, 64) = 5.10, p < .004. A-posteriori comparisons (Fisher’s PLSD) indicated that the mean difference scores for the control group, the clothing-altered group, and the hair-altered group were significantly greater than the mean difference score for the group seeing both hair and clothing altered (M = .257, .lll, .066, and -.166, SD = .053, .160, .173, and .149, respectively, p < .05). No differences due to sex of subject or sex of stimulus pictures and no interactions were found. The a-priori t tests on group data, comparing mean log fixation times for the generalization and recovery trials to the mean of the posthabituation trials, showed significant recovery to the opposite-sex face for only the control group (the 12-month-old infants from Experiment 1). The group seeing only clothing altered were expected to detect the change to an opposite-sex face, but, although the infants generalized habituation to the new same-sex face, their mean fixation times for the recovery trial were not significantly greater than for the posthabituation and generalization trials (t = 1.23, p < .12; and t = 1.33, p < .ll). Means and standard deviations of the posthabituation, generalization, and recovery trials for the four stimulus conditions are presented in Table 2. Individual Data. The criteria for recovery in individual infants were the same as in Experiment 1. The proportion of control-group infants showing recovery (.45) did not differ significantly from that of the group seeing men
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LEINBACH
AND
TABLE Mean
tog
Fixation Times for Posthobituotion, for lnfonts in Control and Three
FAGOT
2 Generolizotion, Altered-Stimulus
ond Recovery Conditions
Trials
Triols
Condition0 Control Unisex
clothes
Short hoir Unisex clothes,
short
hair
Posthobituotion
Generolizotion
Recovery
M (SD)
M (SD)
M (SD)
1.159 1.281 1.157
(0.215) (0.236) (0.195)
1.133 1.252 1.237
(0.264)
1.223
(0.368)
1.384
(0.176)
1.304
(0.271)
1.218
(0.325)
Note. Recovery wos ottributed only to those groups whose trio1 were significantly greater thon those for the posthobituotion not achieved by any stimulus-oltered condition. On = 20 for each group.
(0.274) (0.277)
meon fixation times and generolizotion
1.4 16 (0.268) 1.392 (0.396)
for the recovery trials and wos
and women in unisex clothing (.40), or from that of the group seeing women with shortened hair and both sexes with unaltered clothing (.30). The proportion of infants seeing both hair and clothing altered (. 15) was significantly less than the proportion showing recovery in the control group (z = 2.07, p < .04). The proportions of infants showing recovery in each stimulus condition are presented in Figure 3. Whether considered separately from the control group or with the control group included, the groups seeing altered stimuli did not differ significantly in the proportions of infants showing recovery to faces of men and women, nor in the proportions of boys and girls showing recovery. To summarize, two of the three groups of infants who were shown altered stimulus pictures saw women with shortened hair, but one saw only clothing modified. Because the cue of longer hair was available, the latter group was expected to respond to the change to an opposite-sex face. As a group, these infants fell short of the criteria detecting the change from a face of one sex to that of the other, but they did not show significantly less attention to the opposite-sex face than did infants in the control group, who saw the original unaltered stimuli. Nor did significantly fewer of them meet the individual criteria for categorical recognition of male and female faces. The two remaining groups saw women with shortened hair, and one of these also saw men and women in unisex clothing. Although only the latter group differed significantly from the control group with regard to detecting the change to an opposite-sex face and in the proportion of infants showing categorical recognition of the change, the sequence of proportions of infants succeeding in each group is consistent with the presumed order of difficulty in discriminating male and female faces. That is, the poorest performance was given by infants for whom the sex-typical cues of both hair length and clothing were attenuated or removed, whereas the performance of infants seeing only
GENDER SCHEMATIC
UNISEX
CLOTHES
SHORT
HAIR
SHORT
HAIR
UNISEX
STIMULUS Figure 3. Proportion
329
PROCESSING
AND
CLOTHES
CONDITION
of infants in each stimulus condition
meeting criteria for recovery.
clothing altered was closest to that of the control group. Thus, it is possible that some of the infants were making use of hair length and sex-typed clothing either as jndividual or redundant cues in discriminating men and women. GENERAL
DISCUSSION
Together, the results of Experiments 1 and 2 indicate that categorical recognition of men and women is to be expected of 9- and lZmonth-old infants, is within the capabilities of some infants as young as 5 months of age, and can be demonstrated by some lZmonth-olds even when hair or clothing, or both, are altered to make the sexes appear more similar. These findings indicate that infants under 1 year of age have incipient categories for men and women, and that the categories may include information about sex-typical hair length and clothing styles. In light of Fagan and Singer’s (1979) finding that 5- to &month-old infants familiarized with a single male or female face will recognize even a highly similar opposite-sex face as novel, and Cohen and Strauss’s (1979) demonstration of categorical responding to female faces at 7 months, we were surprised that the 7-month-olds in Experiment 1 did not make a stronger showing. Fagan and Singer used a long familiarization presentation (two 30-s exposures to one face), which undoubtedly led to more thorough processing of the face. Because both the familiar and novel faces were presented for the test trials and displayed few differences other than gender, trying to process what discrepant information was available may have led the infants to search the novel face and, consequently, to indicate greater awareness of gender. The categorical habituation procedure we used requires the infant to extract the information that remains constant across a set of variable stimuli, a more difficult task. However, our procedure was virtually identical to that of Cohen and Strauss except for the presentation of an opposite-sex test trial; unless our
330
LEINBACH
AND FAGOT
7-month-olds were in some way atypical, it may be that many infants in both studies had habituated to faces in general, rather than to faces of one sex or the other. The possibility that hair length and sex-typical clothing can serve as cues for discriminating pictures of men and women does suggest caution in attributing conceptual categories, on the basis of habituation studies, to infants who may be responding to fairly superficial features. In responding to the limited information available in a photograph, the presence or absence of a specific cue may be sufficient to produce the habituation-recovery effect in some infants. Indeed, the presence of a salient feature may determine whether a stimulus will be discriminated on a perceptual or a conceptual basis (Kestenbaum & Nelson, 1990). We cannot say for certain that infants use hair and clothing cues to distinguish males and females, or whether, alternatively, they may be attending only to these cues. But even if some infants were to derive a category system comprised of long- and short-haired people, those categories would be differentially associated with males and females in our society. The infants in Experiment 2 who responded with renewed interest to an opposite-sex face were apparently observant enough to recognize the change from a face of one sex to that of the other even with hair and clothing made more similar, but we do not know what information about faces had become associated with either sex for them. Regardless of the nature of the developing categories, the demonstration of categorical perception of male and female faces, along with evidence that changes in hair and clothing style may influence gender recognition, indicate that perceptually available differences have begun to organize the processing of information along genderdimorphic lines. The greater recovery shown by infants who were habituated to a male face and tested with a female face raises the issue of preference which, although beyond the scope of this article, could be resolved using a standard visual preference paradigm. It is conceivable that young infants simply prefer to look at a female face. There could be other explanations, also. For example, Langlois, Ritter, Roggman, and Vaughn (1991) found that, with emotional cues held constant, 6-month-old infants preferred to look at attractive rather than unattractive adult faces of both sexes, but 7-month-olds in Nelson and Dolgin’s (1985) study generalized habituation to facial expressions of fear and happiness across male and female faces. Such findings suggest that young infants are sensitive to various aspects of faces, and that a number of variables, separately or together, could augment or reduce the salience of gender as a category of immediate interest. In this experiment, expression was varied intentionally to approximate conditions in ordinary life, and, although all of the stimulus faces were fairly attractive, we cannot be sure that subtle differences in expression or attractiveness did not contribute to the greater recovery of infants when the recovery stimulus was a female face. However, the same faces were used in Experiment 2, where no preference was evident.
GENDER SCHEMATIC PROCESSING
331
Once infants have begun to incorporate sex-differentiated attributes into other information being encoded, the basis of a gender schema has been established. We should expect this to be the case. Given that the world of the infant is peopled with examples of both sexes and that gender serves as an organizing principle around which all societies build social categories, it would be surprising indeed if infants’ early categorization abilities failed to make use of so important a real-world category system as the distinction between female and male. REFERENCES Bern, S.L. (1981). Gender schema theory: A cognitive account of sex typing. Psychological Review,
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Cornell, E.H. (1974). Infants’ discrimination of faces following redundant presentations. Journal of Experimental Child Psychology, 18. 98-106. Fagan, J.F. (1976). Infants’ recognition of invariant features of faces. Child Development, 47, 627-638. Fagan, J.F., & Singer, L.T. (1979). The role of simple feature differences in infant recognition of faces. Infant Behavior and Development, 2, 39-46. Horowitz, F.D. (1975). Visual attention, auditory stimulation, and language discrimination in young infants. Monographs of the Society for Research in Child Development, 39(5-6, Serial No. 158). Horowitz, F.D., Paden, L., Bhana, K., & Self, P. (1972). An infant control procedure for Psychology, 7, 90. studying infant visual fixations. Developmental Itons-Peterson, M.J. (1988). Children’s concepts of gender. Not-wood, NJ: Ablex. Jusczyk, P.M., Pisoni, D.B., & Mullenix, J. (1992). Some consequences of stimulus variability on speech processing by two-month-old infants. Cognition, 43, 253-291. Kestenbaum, R., & Nelson, C.A. (1990). The recognition and categorization of upright and inverted emotional expressions by 7-month-old infants. Infant Behavior and Development, 13, 497-511. Langlois, J.H.. Ritter, J.M., Roggman, L.A., & Vaughn, L.S. (1991). Facial diversity and infant preferences for attractive faces. Developmental Psychology, 27, 79-84. Lewis, M., & Brooks, J. (1974). Self, other, and fear: Infants’ reactions to people. In M. Lewis & L. Rosenblum (Eds.), The origins of behavior: Vol. 2. The origins of fear. New York: Academic. Martin, C.L., & Halverson, C.F. (1981). A schematic processing model of sex typing and stereotyping in children. Child Development, 52, 1119-l 134. Miller, C.L. (1983). Developmental changes in male/female voice classification by infants. Infants
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Strauss, M.S. (1979). Abstraction of prototypical information by adults and lo-month-old infants. Journal of Experimental Psychology: Human Learning and Memory, 5, 618-632. Younger, B.A., & Cohen, L.B. (1983). Infant perception of correlated attributes. Child Development,
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7 July 1991; Revised 21 May 1992 W