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Dec 5, 2011 - Developmental Psychology. Is the Face-Perception System Human-Specific at Birth? Elisa Di Giorgio, Irene Leo, Olivier Pascalis, and ...
Developmental Psychology Is the Face-Perception System Human-Specific at Birth? Elisa Di Giorgio, Irene Leo, Olivier Pascalis, and Francesca Simion Online First Publication, December 5, 2011. doi: 10.1037/a0026521

CITATION Di Giorgio, E., Leo, I., Pascalis, O., & Simion, F. (2011, December 5). Is the Face-Perception System Human-Specific at Birth?. Developmental Psychology. Advance online publication. doi: 10.1037/a0026521

Developmental Psychology 2011, Vol. ●●, No. ●, 000 – 000

© 2011 American Psychological Association 0012-1649/11/$12.00 DOI: 10.1037/a0026521

Is the Face-Perception System Human-Specific at Birth? Elisa Di Giorgio and Irene Leo

Olivier Pascalis

Universita` degli Studi di Padova

Universite` Pierre Mendes

Francesca Simion Universita` degli Studi di Padova The present study investigates the human-specificity of the orienting system that allows neonates to look preferentially at faces. Three experiments were carried out to determine whether the face-perception system that is present at birth is broad enough to include both human and nonhuman primate faces. The results demonstrate that the newborns did not show any spontaneous visual preference for the human face when presented simultaneously with a monkey face that shared the same features, configuration, and low-level perceptual properties (Experiment 1). The newborns were, however, able to discriminate between the 2 faces belonging to the 2 different species (Experiment 2). In Experiment 3, the newborns were found to prefer looking at an upright, compared with an inverted, monkey face, as they do for human faces. Overall, the results demonstrate that newborns perceive monkey and human faces in a similar way. These findings are consistent with the hypothesis that the system underlying face preference at birth is broad enough to bias newborns’ attention toward both human and nonhuman primate faces. Keywords: face detection, newborns, human face, monkey face, face-perception system

broad face representation (Johnson & Morton, 1991). In contrast, some authors maintain that newborns’ face representation might be sufficiently detailed from birth (Meltzoff & Moore, 1977; Slater & Kirby, 1998; Slater et al., 1998). Data supporting this hypothesis have been generated by several studies that have demonstrated that newborns imitated a variety of facial gestures. This result is difficult to explain if the infant does not have a representation of his or her own face (Meltzoff & Moore, 1977). Quinn and Slater (2003) hypothesized that face representation is the product of evolutionary pressure and would benefit from proprioception in utero. Indeed, proprioceptive feedback provided by facial movements could contribute to the formation of a face-specific representation that is present at birth. Currently, most theorists agree that the face-perception system at birth is the product of a conjunction of evolutionary inheritance, in utero learning, and rapid learning after birth (de Schonen, 1989; Pascalis & Kelly, 2009; Sai, 2005; Slater et al., 2010). In other words, in the same way that evolutionary selection builds a neural “scaffolding” that facilitates language learning, a similar mechanism facilitates the development of the face-perception system. Several studies support the notion that early learning with regard to faces happens from birth. According to Walton and Bower (1993), newborns may even be able to form a face prototype in less than 1 min after birth. The early impact of experience is evidenced by the recognition of individual faces, such as the mother’s face over a stranger’s face (Bushnell, Sai, & Mullin, 1989; Field, Cohen, Garcia, & Greendburg, 1984; Pascalis, de Schonen, Morton, Deruelle, & Fabre-Grenet, 1995). In addition, intersensory contingency facilitates learning at birth; newborns show a preference for their mother’s face if they have had postnatal exposure to the mother’s voice and face paired together (Sai, 2005). According to some authors, the face-perception system becomes “tuned” to human faces as a direct consequence of extensive

The human visual world is complex and full of rich visual stimuli. Among these numerous visual inputs, the human face, because of its biological and social relevance, is one of the most salient. A few hours after birth, the newborn’s visual attention is preferentially attracted to faces over other complex visual stimuli (Fantz, 1961; Goren, Sarty, & Wu, 1975; Johnson & Morton, 1991; Macchi Cassia, Turati, & Simion, 2004; Valenza, Simion, Macchi Cassia, & Umilta`, 1996). These data suggest that humans may be born with a template or representation of the human face (Johnson & Morton, 1991). However, the role of these innate biases and of the rapid early learning involved in shaping the face-perception system remains an open question (de Schonen, 1989; de Schonen, Mancini, & Leigeois, 1998). The hypothesized existence of special mechanisms for face detection at birth suggests that newborns may begin life with a

Elisa Di Giorgio and Irene Leo, Dipartimento di Psicologia dello Sviluppo e della Socializzazione, Universita` degli Studi di Padova, Padova, Italy; Olivier Pascalis, Laboratoire de Psychologie et Neurocognition, Universite` Pierre Mendes, Grenoble, France; Francesca Simion, Dipartimento di Psicologia dello Sviluppo e della Socializzazione, Universita` degli Studi di Padova, Padova, Italy. Research was supported by Ministero dell Universita` Grant 2007XFM93B_004 and University of Padua Grant 2007-CPDA075245, awarded to Francesca Simion. Elisa Di Giorgio was supported by a PhD Grant from Fondazione della Cassa di Risparmio di Padova e Rovigo. We thank Dalla Barba and the nursing staff at the Pediatric Clinic for their collaboration. Correspondence concerning this article should be addressed to Elisa Di Giorgio, Dipartimento di Psicologia dello Sviluppo e della Socializzazione, Universita` degli Studi di Padova, via Venezia 8, 35131 Padova, Italy. E-mail: [email protected] 1

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experience of faces provided by the species-typical environment within the first days of life (Nelson, 2003; Scott, Pascalis, & Nelson, 2007). However, how general the face-perception system is at birth and the role of visual experience in shaping this system remain open questions. Specifically, it appears to be relevant to determine whether the face-perception system at birth is speciesspecific or broad enough to draw newborns’ attention toward faces belonging to different species, such as human and nonhuman primate faces (de Schonen, 1989). A dramatic demonstration of the existence of a broad faceperception system, which becomes specialized as a function of early visual input, is given in Sugita’s (2008) study. Infant Japanese macaques (Macaca Fuscata) were separated from their parents at birth and reared by human caregivers who wore masks to ensure that the monkeys were not exposed to faces of any kind for a period of 6 –24 months. Following the face-deprivation period, the monkeys were then introduced to either fellow macaques or humans. When tested for face preference during the deprivation period, the monkeys showed a preference for both monkey and human faces over objects but no preference for either category of face when they were presented simultaneously. When the monkeys were tested a month after the end of the deprivation period, their behavioral performance had changed dramatically. The monkeys that were exposed to human faces retained their preference for human faces over objects, but they also preferred to look at human faces over monkey faces. The monkeys that were exposed to monkey faces preferred monkey faces over human faces. Surprisingly, the period of deprivation did not have a significant impact on their performance in preference or recognition tasks at any stage. This study demonstrated that the face-perception system is not species-specific at birth, at least in monkeys, and that only extensive experience with one kind of face had an impact on shaping and specializing the system. A demonstration of the impact of experience in shaping the face-perception system of humans can be found in a recent study by Heron-Delaney, Wirth, and Pascalis (2011). This study demonstrated that a few days’ worth of visual experience is sufficient to render the system species-specific, enabling newborns to prefer a human face over a monkey face. Specifically, the nature of infants’ early representations at birth was investigated to disentangle the question of whether newborns, as well as infants, could discriminate humans from nonhuman primates and whether there was a preference for humans from birth and throughout the first 6 months of life. The findings demonstrated that 3.5- and 6-monthold infants paid more attention to pictures of human beings than of nonhuman primates (a gorilla or a macaque). The same preference was observed when infants were presented with the whole body or the face only. A preference for humans was also observed in newborns only in the face-only condition. The authors concluded that newborns’ exposure to human faces during their first few days of life is enough to allow them to develop a representation of human faces that is precise enough to differentiate human from nonhuman primate faces. However, the sensory hypothesis may explain these results. This hypothesis suggests that certain classes of stimuli are preferred by newborns as a result of the general properties of the early stages of early visual processing (Banks & Salapatek, 1981). The sensory hypothesis (based on the prediction of the linear system model) maintains that the attractiveness of a pattern is determined solely

by the effective energy of that pattern. As the stimuli used in Heron-Delaney et al.’s study (2011) were not equated as regards their low-level perceptual properties, the preference that was observed may be due solely to a difference in the visibility of the two stimuli (e.g., a difference in contrast). Moreover, in these pictures, the nonhuman primate faces stand out, as their fur is dramatically different from the humans’ skin. This means that the perceptual cue that the newborns used may have been the presence of fur and not the difference in the global configuration of the two faces. In light of these considerations, the preference for human faces over monkey faces needs to be replicated with stimuli that have been matched for their low-level perceptual properties. The aim of the present study is to determine whether the system which underpins face preference at birth is sufficiently general to bias newborns’ attention equally toward human and nonhuman primate faces that have been equated for all low-level variables. In other words, we aim to investigate whether only a few hours of visual experience with human faces are sufficient to bias newborns’ face-perception system toward human faces. To prevent differences in the perceptual characteristics of the stimuli, such as the presence of fur or different external contours, we equated the two faces for all low-level perceptual properties (i.e., low spatial frequencies and high-contrast areas). The only exception was the eyes, because the contrast between the sclera and the iris of the human eye differs from that of a monkey’s eye. The salience of eyes plays an essential role in learning faces, as previously demonstrated by a computational model of face processing (Acerra, Burnoud, & de Schonen, 2002) and by behavioral studies (Geldar, Maurer, & Carney, 1999; Maurer & Barrera, 1981). Three experiments were carried out to determine whether newborns (a) show a spontaneous preference between a human and a monkey face equated for all low-level perceptual properties (Experiment 1), (b) are able to discriminate between a human face and a monkey face (Experiment 2), and (c) show a preference for an upright monkey face over an upside-down monkey face (Experiment 3).

Experiment 1 In line with previous studies carried out on humans and animals that have demonstrated the existence of a preference for faces at birth (Macchi Cassia et al., 2004; Sugita, 2008), the aim of Experiment 1 was to investigate whether newborns exhibit a spontaneous visual preference for human faces when contrasted with nonhuman primate faces when the stimuli look similar in terms of their global shape and the brightness and contrast are as equal as possible.

Method Participants. Eighteen typical, healthy, full-term Caucasian newborns were recruited from the Paediatric Clinic of the University of Padova, Italy. Six infants were removed from the study for the following reasons: Three changed state during the test (the newborn became too tired or started to cry), and three had a strong position bias (they looked in one direction for more than 80% of the time). Therefore, the final sample consisted of 12 newborns (six boys). All of the infants met the screening criteria of a normal delivery, a birth weight between 2,570 and 3,980 g, and a 5-min

FACE-PERCEPTION SYSTEM AT BIRTH

Apgar score above 8. Their age at the time of testing ranged from 24 to 72 hr. The newborns were tested only if they were awake and in an alert state (Prechtl & O’Brien, 1982) and after the parents had given their informed consent. Stimuli. Grayscale digitized full-frontal images of two human and two monkey faces (Rhesus Macaques) were prepared using Adobe Photoshop 7.0 (see Figure 1). The stimuli were taken from the Psychological Image Collection at Starling (PICS; http:// pics.stir.ac.uk). Two pairs of stimuli comprising a human and a monkey face were presented side-by-side on the screen. The monkey faces were manipulated by removing the hair from the cheeks to equalize the monkey and human faces for all low-level variables (i.e., low spatial frequency, contrast, luminance). The stimuli were approximately 18.5 cm high ⫻ 13.5 cm wide (with a visual angle of approximately 34° ⫻ 26°). Apparatus. The newborn sat on the experimenter’s lap, 30 cm from a 30-in. (76.2-cm) computer screen (2,560 ⫻ 1,600 pixels). The infant’s eyes were aligned with a red flickering LED at the center of the screen, which was used to attract the infant’s gaze at the start of each trial and to check that the infant’s sight was level with the horizontal midline of the screen during the test. Both stimuli were projected bilaterally on a black screen at a distance of approximately 8 cm (15°) from a central fixation point. A video camera, mounted above the central screen, recorded the infant’s eye movements. To prevent interference from irrelevant distracters, plain white curtains were drawn on both sides of the chair on which the experimenter sat with the baby on her lap. Procedure. The experiment was carried out using a preferential looking procedure. Every trial began with the flashing light in the center of the screen. As soon as the infant fixated on the light, one of the experimenters, who was watching the infant’s

Figure 1. and 2.

Human and monkey face images employed in Experiments 1

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eyes by means of a video monitoring system, started the trial sequence by pressing a key on the computer keyboard. This automatically turned off the central LED and activated the slide projector, which presented the stimuli on the screen. The stimuli remained on the screen for as long as the infant fixated on one of them (infant control procedure). When the infant shifted his or her gaze from the display for more than 10 s, the observer turned off the stimuli and the central light turned on automatically. All of the infants underwent two trials in which the two stimuli were shown bilaterally, one on the left and one on the right of the central LED. The left/right position of the stimuli was counterbalanced between the trials. The session ended when the baby did not look at either stimulus for more than 10 s. The videotape of the infant’s eye movements throughout the trial was subsequently analyzed frameby-frame by two coders (an experimenter and a student). Both coders were unaware of the kind of stimulus presented. The coders recorded for each stimulus and each position the total fixation time (i.e., the sum of all fixations) and the number of orienting responses. The mean estimated reliability between the online and offline coding was r(10) ⫽ .90, p ⬍ .001, N ⫽ 12 (Pearson’s correlation) for either dependent variable (total fixation time, discrete number of looks, the duration of the longest fixation and the duration of the first fixation).

Results and Discussion To determine whether the newborns showed a spontaneous visual preference for one of the two stimuli, separate two-tailed dependent samples t tests were performed. As regards the normality of the data distribution, the Kolmogorov-Smirnov test showed that the data were normally distributed. The results showed no evidence of preference for the human face for any of the dependent variables when the group of subjects was considered. Neither the duration of the longest fixation (human face, M ⫽ 13.4 s, SD ⫽ 6.1, vs. monkey face, M ⫽ 12.2 s, SD ⫽ 6.2), t(11) ⫽ 0.48, ns, nor the duration of the first fixation on the human face (human face, M ⫽ 5.2 s, SD ⫽ 3.2, vs. monkey face, M ⫽ 4.1 s, SD ⫽ 3.6), t(11) ⫽ 0.98, ns, reached the level of significance. Furthermore, the newborns did not look at the human face for longer (M ⫽ 33.2 s, SD ⫽ 13.9) than the monkey face (M ⫽ 32.5 s, SD ⫽ 15.1), t(11) ⫽ .09, ns. We conducted additional analyses on preference scores (percentages) for the human face. The length of time for which each infant looked at the human face was divided by the total time spent looking at both test stimuli. The score was then multiplied by 100. Therefore, only scores significantly above 50% indicate a preference for the human face compared with the monkey face. Preference was not above the chance level of 50% (M ⫽ 50%, SD ⫽ 18.1), one-sample t(11) ⫽ 0.12, ns, two-tailed. Six newborns preferred to look at the human face for more than 55% of their total fixation time (M ⫽ 65%). The other six newborns preferred to look at the monkey face for more than 53% of their total fixation time (M ⫽ 62%). Furthermore, if we consider the number of orienting responses, the newborns did not orient more frequently to the human face (M ⫽ 13.2, SD ⫽ 5.5) than the monkey face (M ⫽ 14, SD ⫽ 5.3), t(11) ⫽ .38, ns. Finally, the correlation between the age of the newborns (h) and the preference score was not significant (r ⫽ .06, ns).

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Heron-Delaney et al. (2011) found a preference for human faces over monkey faces during the first week of life in an experimental condition in which hair/fur was not removed. In contrast, our results demonstrate that the newborns did not show any spontaneous visual preference when the two faces were equated for lowlevel perceptual properties, even though the eyes of the two faces differed because of the contrast between the sclera and the iris. One possible interpretation of the lack of visual preference is that the face-perception system during the first week of life has not been shaped to be human-specific. However, this null result should be interpreted with caution, as the newborns may not have been able to differentiate between the two stimuli. Experiment 2 aimed to test this hypothesis.

Experiment 2 Experiment 2 tested whether newborns are capable of discriminating, after habituation, a human face from a monkey face, equated for all low-level perceptual properties.

Method Participants. Seventeen healthy and full-term Caucasian newborns (five boys) from the Paediatric Clinic of the University of Padova were tested. Three newborns changed their state during testing and were excluded from statistical analysis. Therefore, the final sample consisted of 14 newborns. All of the infants met the screening criteria of a normal delivery, a birth weight between 3,100 and 3,980 g, and a 5-min Apgar score between 8 and 10. Their age at the time of testing ranged from 24 to 72 hr. The newborns were tested only if they were awake and in an alert state. Informed consent was obtained from their parents. Stimuli. The same grey scale full-frontal images of the human and monkey faces that were used in the previous experiment were employed in Experiment 2. Apparatus. The apparatus was the same as in Experiment 1. Procedure. The experiment was carried out using an infantcontrol habituation procedure (Horowitz, Paden, Bhana, & Self, 1972). The infant was judged to have habituated when, from the fourth fixation onward, the sum of any three consecutive fixations was 50% or less of the total of the first three fixations (Slater, Earle, Morison, & Rose, 1985). Half of the newborns habituated to the human face, whereas the other half habituated to the monkey face. During the habituation phase, the same stimuli were presented side-by-side. The stimuli remained on the screen until the habituation criterion was reached. A bilateral, rather than central, method of presentation was chosen for two reasons: First, when newborns look at a centrally presented stimulus, it is difficult for an observer to decide whether they are actually looking at the stimulus or simply not moving their eyes from the central position. Second, at birth, the photoreceptors in the central fovea are very immature, resulting in poor vision in the central area of the visual field (Abramov et al., 1982; Atkinson & Braddick, 1989). The habituation phase was followed by two preference tests in which a familiar face and a novel one were presented side-by-side. The left-right position of the stimuli was reversed from the first to the second presentation. Looking at one stimulus, generally the novel one, for a longer period of time indicated discrimination and recognition. During the preference test phase, the experimenter

recorded the duration of the infant’s fixation on each stimulus by pressing one of two different buttons, depending on whether the infant looked toward the right or the left position. The presentation lasted until the infant had fixated on each stimulus on least once and a total of 20 s of looking had been accumulated.

Results and Discussion All of the newborns reached the habituation criterion. A oneway analysis of variance was run to compare the total fixation times to reach the habituation criterion for the two groups of subjects that had habituated to the human face (M ⫽ 37.6 s, SD ⫽ 6.5, trials M ⫽ 9) or the monkey face (M ⫽ 37.4 s, SD ⫽ 7.7, trials M ⫽ 8). The results of the comparison were not significant, F(1, 12) ⫽ 0.006, ns. To test whether the newborns were able to recognize and discriminate between the novel stimulus and the familiar one, a novelty preference score (percentage) was computed. The time that each infant spent looking at the novel stimulus during the two test presentations was divided by the total time spent looking at both test stimuli during the two presentations, and subsequently converted into a percentage score. Hence, only scores that were significantly above 50% indicated a preference for the novel stimulus. The mean novelty preference score was 66.9% (SD ⫽ 8.8), which differed significantly from the chance level of 50%, t(13) ⫽ 20.9, p ⬍ .01 (Cohen’s d ⫽ 1.3; Cohen, 1988). When they were habituated to a monkey face, the newborns exhibited a novelty preference for the human face (69%), whereas when they were habituated to a human face, they displayed a preference for the monkey face (58%). The results of Experiment 2 disprove the assumption that the lack of preference found in Experiment 1 is due to the newborns’ inability to discriminate between the two stimuli. The newborns were shown to be sensitive to differences between the two stimuli and therefore able to discriminate and recognize the familiarized stimulus.

Experiment 3 The purpose of Experiment 3 was to investigate whether the newborns’ preference for monkey faces was altered by their orientation, as has been observed in previous studies using human faces (Macchi Cassia et al., 2004; Turati, Macchi Cassia, Simion, & Leo, 2006). If monkey faces are perceived as human faces, then a preference for an upright monkey face over an inverted monkey face should be found in newborns.

Method Participants. The participants were 12 full-term healthy Caucasian newborns (eight boys), recruited from the maternity ward of the Paediatric Clinic of the University of Padova. One other newborn was excluded from the final sample because his state changed during testing. All of the infants met the screening criteria of a normal delivery, a birth weight between 2,620 and 3,700 g, and a 5-min Apgar score between 8 and 10. Their age at the time of testing ranged from 24 to 72 hr. The method used to select the newborns was identical to that which was used in Experiments 1 and 2.

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Stimuli. The same grayscale full-frontal monkey face images used in Experiments 1 and 2 were employed (see Figure 2). An upright monkey face was contrasted with the same monkey face that had been inverted. Apparatus and procedure. The apparatus and procedure were identical to those described in Experiment 1.

Results and Discussion To test the newborns’ preferences, one dependent-samples t test (two-tailed) was performed for each dependent variable (duration of the longest fixation and first fixation, total fixation time and number of orientations). The duration of the longest fixation on the upright monkey face (M ⫽ 15.5 s, SD ⫽ 8.2) was significantly different from the duration of the longest fixation on the inverted monkey face (M ⫽ 10.6 s, SD ⫽ 4.1), t(11) ⫽ 2.3, p ⬍ .05 (Cohen’s d ⫽ 0.70). Moreover, the newborns looked at the upright monkey face for significantly longer (M ⫽ 38.7 s, SD ⫽ 15.9) than at the same monkey face that was inverted (M ⫽ 25.5 s, SD ⫽ 7.3), t(11) ⫽ 2.5, p ⬍ .05 (Cohen’s d ⫽ 0.70; see Figure 3). In addition, preference scores for the upright monkey face were above the chance level of 50% (M ⫽ 59%, SD ⫽ 12), t(11) ⫽ 2.5, p ⬍ .05 (Cohen’s d ⫽ 0.70). Furthermore, the t test that was performed on the number of orientations revealed that the newborns did not orient more frequently to the upright monkey face (M ⫽ 12, SD ⫽ 2.7), rather than the inverted monkey face (M ⫽ 10, SD ⫽ 2.1), t(11) ⫽ 1.8, ns. An examination of the data for individual infants found that eight out of the 12 newborns looked at the upright monkey face for longer (binomial tests, ns). Moreover, eight out of the 12 newborns oriented more frequently toward the upright monkey face (binomial tests, ns). The duration of the first fixation did not attain statistical significance (ns). Finally, as in Experiment 1, the correlation between the age of the newborns (h) and the preference score was not significant (r ⫽ .02, ns). The results of Experiment 3 show that, as with human faces, the manipulation of the orientation of a monkey face affects newborns’ visual preferences. This outcome demonstrates that, as for human faces, the newborns showed a preference for the upright monkey face over the same face that had been inverted. The upright orientation effect has already been demonstrated with face-like patterns (Johnson & Morton, 1991; Valenza et al., 1996) and with photographs of real faces (Macchi Cassia et al., 2004).

Figure 2. Stimuli employed in Experiment 3.

Figure 3. Total fixation time on upright monkey face versus inverted monkey face in Experiment 3. ⴱ p ⬍ .05.

The presence of the orientation effect with a primate face can be interpreted as showing that newborns react in the same way to human and monkey faces.

General Discussion The present study aimed to address the question of the speciesspecificity of the human face-perception system within the first few days of life. Starting from a previous study in which a preference for human faces over monkey faces was demonstrated (Heron-Delaney et al., 2011), we investigated whether this preference might be explained by a difference in the low-level perceptual properties of the stimuli. For these reasons, in the present study, the human faces and monkey faces were equated for lowlevel perceptual properties. The results of Experiment 1 demonstrate that the newborns did not show any visual preference for a human face over a face that is human-like (primate face), corroborating the idea that newborns’ face-perception system is not human-specific during the first week of life. The lack of preference must be interpreted cautiously, however, as it may be due to the newborns’ inability to differentiate between the two stimuli that were presented. Experiment 2 disproves this interpretation, because it demonstrates that the newborns were able to discriminate between the two stimuli employed in the preference test in Experiment 1. Finally, Experiment 3 demonstrated that, as with human faces (Macchi Cassia et al., 2004), the manipulation of the orientation of a monkey face affects newborns’ visual preferences. The preference for the upright monkey face is interpreted as demonstrating that newborns react to nonhuman primate faces in the same way as previously demonstrated for human faces. This preference for the upright monkey face can be interpreted in two ways. The first refers to the hypothesis that one critical perceptual property that elicits a face preference in newborns is the presence of a greater number of elements in the upper part of the configuration (i.e., up-down asymmetry; Simion, Valenza, Macchi Cassia, Turati, & Umilta`, 2002). Therefore, newborns may prefer the upright monkey face because of the presence of more elements (i.e., the eyes) in the upper part. The second interpretation refers to the presence of first-order configural information present in the

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monkey face as well as in the human face (Simion et al., 2002). Indeed, recent results using Mooney face patterns (in which features are formed of patches of intense light and shadow only and require closure) support the role of first-order configural information. The results demonstrate that when a Mooney face is contrasted with a Mooney stimulus, such as a butterfly equated for the number of elements in the upper part of the configuration, newborns prefer to look at holistic patterns that are closer to upright faces (Leo & Simion, 2009). There is prominent evidence in support of the proposal that at birth, the face-perception system is broad and unspecified and that it is shaped by the faces that are experienced in the visual environment in the first few months of life (de Schonen & Mathivet, 1989; Nelson, 2001; Sugita, 2008). However, as Nelson (2003) pointed out, it is not clear what kind of experience is necessary and when and for how long this experience needs to occur. The experiments in this study were designed to disentangle these issues. The findings of Experiment 1 are consistent with a large proportion of the literature on face-perception at birth in both animals (Sugita, 2008) and humans (Kelly et al., 2005; Quinn et al., 2008), which reveals clear evidence of a basic, coarsely tuned face-perception system in primates as well as humans at birth. Newborns do not show any visual preference for faces from their own or other ethnic groups (Kelly et al., 2005), and they do not respond differentially to the gender of the faces that are presented (Quinn et al., 2008). The lack of a preference between a monkey face and a human face contradicts previous results that have demonstrated a preference for human faces over monkey faces in newborns (HeronDelaney et al., 2011). However, in the study in question, the monkey and human faces were not equated for low-level perceptual properties. A possible alternative interpretation could be based on the sensory hypothesis (Banks & Salapatek, 1981), as the two stimuli differed in terms of the amount of effective energy in the two patterns. Consequently, a more parsimonious interpretation is that newborns’ preference for human faces may be due to the physical and perceptual characteristics of the pictures used. Importantly, the only perceptual characteristic that differentiates the two stimuli in the present study is the presence in the human face alone of the correct contrast polarity within the eyes (i.e., a black pupil surrounded by a white sclera). The human species is the only primate species with a white sclera and a dark iris (Kobayashi & Kohshima, 1997). Although the presence of this perceptual characteristic might explain newborns’ discrimination in Experiment 2, it fails to explain the absence of a preference for the same stimuli in Experiment 1. In addition, the results of Experiment 2, which show that newborns are able to discriminate between human and monkey faces, extend our knowledge of the face-perception system and are consistent with the literature. Indeed, previous studies have demonstrated that newborns are able to discriminate between faces from their own ethnic group (Pascalis & de Schonen, 1994) on the basis of both the inner features and the outer contours (Turati et al., 2006). Overall, our results show that newborns do not respond differently to human and monkey faces, showing that the human faceperception system is rather broad during the first week of life. The presence of a preference for the upright monkey face in Experiment 3 corroborates our conclusion that newborns react in the same way to human and monkey faces. Nonhuman primates

clearly share a similar face arrangement to humans that can be expected to be processed in a similar way. Campbell et al. (1997) explored this hypothesis by testing adult human subjects’ categorical perceptions of three categories of various computer-morphed faces: human-monkey, monkey-cow, and human-cow faces. The authors showed that the perceptual discrimination boundaries for monkey-human morphs were less distinct than for monkey-cow or human-cow faces. Therefore, in adults, a single category formed the basis for the discrimination of both human and monkey faces, suggesting that similar mechanisms are involved in processing these two categories of stimuli (Campbell et al., 1997). The present study, in addition to extending our knowledge of the face-perception system at birth, opens up some intriguing questions. Do newborns process monkey faces as human faces? Do human faces and monkey faces belong to the same category? To what degree is newborns’ face representation “primate”-like? In effect, if a primate face representation exists during the first few days of life, at birth, we should observe a systematic preference for human and nonhuman primate faces over faces belonging to other species (e.g., dog, cow, bird). Starting from a recent study that showed that 4- to 6-month-old infants, but not 9- to 11-month-old infants, were able to discriminate nonprimate faces (i.e., sheep faces) from primate ones (Simpson, Varga, Frick, & Fragaszy, 2011), it could be interesting to investigate whether infants’ faceperception system is broadly attuned at the beginning not only to primate faces but to nonprimate faces as well. A second series of questions that remains open concerns the role of eyes. It has been suggested that eyes are important in determining newborns’ orientation toward faces (Acerra et al., 2002; Batki, Baron-Cohen, Wheelwright, Connellan, & Ahluwalia, 2000; Farroni, Csibra, Simion, & Johnson, 2002). The results of the present study seem to show that the contrast between the sclera and the iris, which is present in human eyes, does not determine any preference. Future studies should investigate what visual properties render human eyes so attractive from birth. Overall, data are in line with the hypothesis that the faceperception system is not human-specific after a few days of life and demonstrates that a few hours of visual experience of human faces is not enough to render the system human-specific. The results corroborate the existing literature on face-perception and provide evidence of the presence of a face-perception system that is not human-specific at birth but that biases newborns’ visual attention toward human and nonhuman primate faces. Because of visual experience of a species-specific environment, this faceperception system becomes tuned to human faces during development (Nelson, 2001; Pascalis, de Haan, & Nelson, 2002; Pascalis & Kelly, 2009). This conclusion is supported by studies demonstrating that 3 months’ worth of visual experience is sufficient not only to induce a gender (Quinn, Yahr, Kuhn, Slater, & Pascalis, 2002), own-species (Heron-Delaney et al., 2011), and own-race preference (Kelly et al., 2005) but also an own-race effect in face processing (Sangrigoli & de Schonen, 2004).

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Received January 7, 2011 Revision received September 30, 2011 Accepted October 14, 2011 䡲