Recognition of Faces of Different Species: A Developmental Study Between 5 and 8 Years of Age

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1 Infant and Child Development Inf. Child Dev. 10: (2001) DOI: /icd.245 Recognition of Faces of Different Species: A Developmental Study Between 5 and 8 Years of Age Olivier Pascalis a, *, Elisabeth Demont b, Michelle de Haan c and Ruth Campbell d a The University of Sheffield, Department of Psychology, Sheffield, UK b Université Louis Pasteur, Strasbourg, France c Institute of Child Health, UCL, London, UK d Human Communication and Science Department, UCL, London, UK There is developmental progression in the ability to recognize human faces (HF) during childhood, accompanied by qualitative differences in what children perceive and remember. The best known example is that of sensitivity to vertical orientation: while there is age-related improvement in recognizing upright faces, upside-down ones show no recognition improvement. It is believed by some investigators to be a sign of developing faceexpertise over the first 10 years or so of life. If expertise, based on experience with many individuals, is the basis for the development of the inversion-effect, faces from other species should not induce inversion-effects. In two experiments, we explored the expertise phenomenon by testing recognition of faces of different animal species with children between 5 and 10 years of age. Our results failed to show any developmental changes in the processing of faces of own- and other-species. Copyright 2001 John Wiley & Sons, Ltd. Key words: children; faces; force choice task A dramatic developmental progression is observed in face recognition from infancy to adulthood. If numerous changes occur during the first year of life (de Haan and Halit, 2001), a developmental enhancement in the ability to recognize human faces (HF) is still observed during childhood (Carey, 1992; Campbell et al., 1995, 1999). The exact nature and causes of the changes, however, are still not well understood. Nelson (this issue) draws a parallel between the development of language and the development of face recognition. He proposes that the face-processing system develops during the first years of life from a broad non-specific system to a human-tuned face processor. In his view, the specificity of the face recognition system to HF will increase with age, and with experience in processing HF. * Correspondence to: The University of Sheffield, Department of Psychology, Sheffield S10 2TP, UK. Copyright 2001 John Wiley & Sons, Ltd.

2 40 O. Pascalis et al. One change in face-processing that occurs during childhood is the emergence of the inversion-effect the phenomenon that inversion disproportionately impairs recognition of HF relative to recognition of other objects. There is debate concerning the specific factor(s) responsible for the facial inversion-effect. Rhodes (1995) claims that relational or higher-order-feature information, such as the distance between the eyes, or between lips and chin, is orientation-sensitive. In Rhodes view, what develops in childhood is the ability to use representations of faces that make use of relational features. By contrast, work by Farah et al. (1995) suggests that the holistic or global aspect (captured, for instance, by coarse quantization of the face or by low-spatial frequency filtering) is orientation-sensitive and that this is sufficient to account for inversion-effects in face recognition. Diamond and Carey (1977) initially found that this effect did not emerge until 10 years of age, and showed that the development progression was a result of age-related improvements in recognizing upright, but not inverted, faces. Since then, further studies have shown that, under certain circumstances, even children as young as 7 years of age (Flin, 1985) are better at recognizing upright than inverted HF. Diamond and Carey (1986) argued that the emergence of the inversion-effect is based on experience in processing many individual faces. If so, then non-hf, even if they share similarities with HF, need not induce inversion-effects. We have recently investigated this hypothesis by testing adults recognition for individual faces of other species with a forced choice task (Pascalis et al., 1998). Adults were good at recognizing HF, monkey faces (MF) and sheep faces (SF). However, the results pointed to qualitatively different processing of primate faces compared with SF. An inversion-effect was found for HF and MF, but not for SF. This suggests that adults process primate faces in a qualitatively different way from SF. We suggested that our results might reflect that, even though the adults were not experts in recognizing MF, they might have used their HF template to process the MF, thereby inducing an inversion-effect. The HF template is, however, not designed to be efficient in processing other primate faces. We showed, with a visual paired-comparison task, administered in identical fashion to both humans and monkeys, that human participants were more skilled at recognizing individual HF than MF, while the opposite was true for monkeys (Pascalis and Bachevalier, 1998). The aim of the present study was to determine whether children, who have less experience with faces than adults, would show a different pattern of responding to HF and MF than did adults. In two experiments, we explored the recognition of upright and inverted faces of different animal species by children between 5 and 8 years of age. We predicted that the youngest group, who have relatively more limited experience with (human) faces, should present a pattern of results different from the other groups tested. They may fail to show an inversion-effect for any type of face, whereas the older group should give an inversion-effect for both HF and MF, but possibly not for SF. EXPERIMENT I Method Participants Thirty-seven children from the Ziegleau School in Strasbourg, who had volunteered to take part in the study, and for whom written parents consent

3 Recognition of Faces of Different Species 41 was obtained were tested. None had personal experience of individual macaque monkeys, nor of sheep. There were 18 (nine boys, nine girls) 6 7-year-old children (mean age=6.9; range= ), and 19 (12 boys, seven girls) 8-yearold children (mean age=8.4; range=8 8.11). Stimuli The stimuli were presented on a video monitor. They were 60 halftone images of faces from three categories: human (Caucasians), monkey (rhesus macaque and tonkeanas macaque) and sheep (examples displayed on Figure 1). The pose was always full-face, top-lit. The face outline was masked to ensure that no neck or background information was seen. All faces were captured with a neutral expression (closed mouth, open eyes, normal muscle tone). In addition, for HF, individuals had no jewellery, glasses or obvious make up. The size of the image was 10 6 cm, presented at a 30 cm viewing distance. Brightness and contrast levels for all images were computationally manipulated to be uniform across pictures in the three categories. Figure 1. Examples of the MF, HF and SF used in the experiments.

4 42 O. Pascalis et al. Procedure A two-alternative forced choice task was used. Participants were tested individually, seated 30 cm in front of a computer screen in a quiet room. Each participant was instructed that one picture would appear on the screen for a 1-s familiarization period, and that they would then be asked to recognize it from a pair of two images. Following the 1-s display of the target image, there was a 3-s unfilled interval, then two pictures (the familiar one and a novel from the same category) were simultaneously presented until the participant had pointed to the picture he/she felt they had seen before. They were asked to be as accurate as possible. The left right position of the novel stimulus was counterbalanced across trials. A prior training period with geometric patterns was carried out and repeated until subjects reached 100% correct responses. Then all the participants were tested first with the upright HF. The other five conditions were also blocked, but presented in a random order: these five conditions were HF inverted, MF upright, MF inverted, SF upright, and SF inverted. There were ten trials for each condition. A criterion of five errors for the upright HF was used to reject subjects. If they were unable to do the task with HF, it was evidence of misunderstanding of the instructions; however, no subjects were rejected from Experiment I. Results The number of errors was scored for each participant for each condition. A three-way within-subjects analysis of variance (ANOVA) (2 age 3 species 2 orientation) showed a significant effect for age (F(1,35)=29.35, p 0.01). Overall, accuracy for faces increased significantly with age (a mean of 3.49 errors for the youngest and 2.11 for the oldest groups). There was a significant effect of species (F(2,70)=18.09, p 0.01). Recognition was better for the HF (mean= 2.15 errors), than for MF (mean=2.77 errors) than for SF (mean=3.49 errors). There was a significant effect of orientation (F(1,35)=21.94, p 0.01). Upright faces (mean=2.44 errors) were better recognized than inverted faces (mean= 3.17 errors). The only significant interaction was between orientation and species (F(2,70)=4.37, p 0.05). Table 1 shows the nature of the species differences: only primate faces induced an inversion-effect, while accuracy for upright and inverted SF did not differ. The responses were, however, better than chance for all the categories. Discussion Accuracy improved with age for this face recognition task. However, the qualitative pattern was similar across the age groups. Like adults, both younger and older children showed an inversion-effect, which was specific to primate faces. Table 1. Age Experiment I: errors (mean (S.D.)) in face recognition for HF, MF and SF Human Human Monkey Monkey Sheep Sheep upright inverted upright inverted upright inverted (1.6) 3.44 (1.2) 3.05 (1) 3.72 (1.4) 4.4 (1.5) 4.2 (1.5) (1) 1.89 (1.4) 1.42 (0.8) 2.89 (1.6) 2.52 (1.5) 2.8 (1.47)

5 Recognition of Faces of Different Species 43 Thus, Flin s finding that an inversion-effect can be found in children before 10 years of age can be extended to younger children, and the effect also generalizes to faces of other primates. One way in which this could happen is if the representational template for recognizing HF can also be used for judging MF (see Campbell et al., 1997). EXPERIMENT II A second experiment was designed to investigate if younger children with less experience with faces would behave similarly to 6 8-year-olds. Method Participants Fifty-seven children from the Ziegleau School in Strasbourg, who had volunteered to take part in the study, and for whom written parents consent was obtained were tested. None had personal experience of individual macaque monkeys, nor of sheep. Only five 5-year-old children did not reach the criterion of less than five errors for upright faces and were rejected from the final sample. There were 20 (10 boys, 10 girls) 5-year-old children, (mean age=5.4; range= 5 5.8); 17 (nine boys, eight girls) 6 7-year-old children (mean age=6.8; range= ); and 20 (10 boys, 10 girls) 8-year-old children (mean age=8.5; range= ). Procedure The procedure was the same as for Experiment I, except that the familiarization period was increased from 1 to 5 s to ensure a sufficient encoding of the stimulus by the younger group. Indeed, Pascalis and de Haan (in press) showed that the younger the child is, the more familiarization time is needed for the stimulus to be fully encoded. The stimuli were the same as those used in Experiment I. Results The number of errors was scored for each participant for each condition. A three-way within-subjects ANOVA (3 age 3 species 2 orientation) showed a significant effect for age (F(2,55)=4.95, p 0.01), the overall accuracy for HF and other species faces increases significantly with age (2.42 errors at 5 years of age, 2.05 errors at 6 7 years of age and 1.7 errors at 8 years of age). There was a significant effect of species (F(2,110)=49.49, p 0.01). Recognition accuracy was better for HF (mean=1.39 errors) than for MF (mean=1.81 errors), and than for SH (mean=2.98 errors). There was a significant effect of orientation (F(1,55)=15.44, p 0.01), with upright faces being better recognized than inverted faces (mean=1.18 errors for upright, and 2.34 for inverted faces). Table 2. Experiment II: errors (mean (S.D.)) in face recognition for HF, MF and SF Age Human Human Monkey Monkey Sheep Sheep upright inverted upright inverted upright inverted (0.74) 2.6 (1.2) 1.8 (1.33) 3 (1.87) 3.1 (1.06) 3.1 (1.64) (0.93) 1.35 (1.2) 0.82 (0.95) 2.47 (1.8) 3.2 (1.74) 3.3 (1.26) (0.67) 1.8 (1.08) 1.22 (0.80) 2.4 (1.56) 3.1 (2) 2.8 (1.47)

6 44 O. Pascalis et al. The only significant interaction was between orientation and species (F(2,110)=11.24, p 0.01). Table 2 shows the nature of the species differences: only primate faces induce an inversion-effect, the number of errors for upright and inverted sheep is equivalent for each age group. As in Experiment I, the responses were better than chance for all the categories. Discussion This experiment showed that 5-year-old children s face recognition is not as accurate as that one observed in older children, but it is more adult-like than expected, because the human and primate inversion-effect was clearly present. Like adults and older children, the 5-year-olds gave an inversion-effect for both HF and MF, but not for SF. GENERAL DISCUSSION The hypothesis that guided this study was that sensitivity to inversion should develop throughout childhood and that it may be selective for HF. MF were predicted to show inversion sensitivity in older children. Our results failed to show any developmental changes, other than in general accuracy, in the processing of faces of own- and other-species. The average number of errors decreases from 5 to 8 years of age. This may be the first demonstration of an inversion-effect for face recognition in 5-year-old children. The finding of a better ability to process upright faces than inverted faces is consistent with Tanaka et al. (1998), who showed that 6-year-old children can process faces holistically. If sensitivity to inversion is taken as an index of face-processing selectivity (Yin, 1969), then it would seem to be accomplished by the age of 5 years. It is more likely, however, that there are a number of performance measures of face-expertise, and that these may follow different developmental trajectories, with relatively different levels of reliance on configural (or low spatial frequency) processing. Familiar or known faces may behave differently than unknown faces in this regard. With respect to unknown faces, however, forced choice recognition can be achieved in an adult-like fashion, both in terms of species and of orientation specificity, by the age of 5 years. In terms of Nelson s model (this volume), the face module has become tuned to the characteristics of the primate face by this age. REFERENCES Campbell R, Walker J, Baron-Cohen S The development of differential use of inner and outer face features in familiar face identification. Journal of Experimental Child Psychology 59(2): Campbell R, Pascalis O, Coleman M, Wallace SB, Benson PJ Are faces of different species perceived categorically by human observers? Proceedings of the Royal Society of London Series B Biological Sciences 264: Campbell R, Walker J, Benson PJ, Wallace SB, Coleman M, Michelotti J, Baron-Cohen S When does the inner face advantage in familiar face recognition arise and why? Visual Cognition 6: Carey S Becoming a face expert. In Processing the Facial Image: Proceedings of a Royal Society Discussion Meeting, Bruce V, Cowey A, Ellis AW, Perrett DI (eds). Clarendon Press: Oxford;

7 Recognition of Faces of Different Species 45 Diamond R, Carey S Developmental changes in the representation of faces. Journal of Experimental Child Psychology 23: Diamond R, Carey S Why faces are and are not special: an effect of expertise. Journal of Experimental Psychology, General 115: de Haan M, Halit H The development and neural basis of face processing during infancy. To appear in Brain and Behavior in Human Development: A Sourcebook, Kalverboer AF, Gramsbergen A (eds). Farah M, Tanaka J, Drain HM What causes the face inversion effect? Journal of Experimental Psychology Human Perception and Performance 21: Flin R Development of face recognition: an encoding switch? British Journal of Psychology 76: Pascalis O, Bachevalier J Face recognition in primates: a cross species study. Behavioural Processes 43: Pascalis O, de Haan M. In press. Recognition memory and novelty preference: what model? Progress in Infancy Research. Pascalis O, Coleman M, Stirnemann M, Petit O, Campbell R Primates first? Expertise affects the ability to identify individuals within and across species. Abstract 132b. Perception 27: 132. Rhodes G Face recognition and perceptual coding. In Cognitive and Computational Aspects of Face Recognition, Valentine T (ed.). Routledge: London; Tanaka JW, Kay JB, Grinnell E, Stansfield B, Szechter L Face recognition in young children: when the whole is greater than the sum of its parts. Visual Cognition 5(4): Yin RK Looking at upside-down faces. Journal of Experimental Psychology 81: