Newborns Face Recognition: Role of Inner and Outer Facial Features

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1 Child Development, March/April 2006, Volume 77, Number 2, Pages Newborns Face Recognition: Role of Inner and Outer Facial Features Chiara Turati University of Padua Viola Macchi Cassia University of Milano-Bicocca Francesca Simion and Irene Leo University of Padua Existing data indicate that newborns are able to recognize individual faces, but little is known about what perceptual cues drive this ability. The current study showed that either the inner or outer features of the face can act as sufficient cues for newborns face recognition (Experiment 1), but the outer part of the face enjoys an advantage over the inner part (Experiment 2). Inversion of the face stimuli disrupted recognition when only the inner portion of the face was shown, but not when the whole face was fully visible or only the outer features were presented (Experiment 3). The results enhance our picture of what information newborns actually process and encode when they discriminate, learn, and recognize faces. The study of newborns face processing has played a prominent role in the developmental field within the last two decades (de Haan, 2001; Johnson & Morton, 1991; Pascalis & Slater, 2003). Interest in this topic mainly derives from the demonstration that highly schematized face-like configurations, as well as images of real faces, spontaneously capture newborns attention more than other, equally complex, visual objects (Johnson & Morton, 1991; Macchi Cassia, Turati, & Simion, 2004; Valenza, Simion, Macchi Cassia, & Umiltà, 1996). Much research focused on the attempt to investigate the origins of the newborns face-preference phenomenon, with the aim of understanding the extent to which this effect is specific to the face category (Johnson & Morton, 1991; Kleiner, 1993; Simion, Macchi Cassia, Turati, & Valenza, 2003; Turati, 2004). Notwithstanding the relevance of this issue, the wide-ranging and prolonged focus on newborns preferential response to faces has overshadowed the interest in other important aspects of newborns face processing, such as newborns ability to learn and recognize individual faces. Face recognition refers to The research reported here was supported by a grant from the Italian Ministry of University and Scientific and Technological Research ( _001). We are deeply indebted to Prof. F. Zacchello, Dr. B. Dalla Barba, and the nursing staff at the Pediatric Clinic of the University of Padua for their collaboration. We also thank S. Bettella for writing the software, and L. Zanon for assistance with infant testing. Special thanks are due to the parents of the infants that took part in the study. Correspondence concerning this article should be addressed to Chiara Turati, Department of Developmental and Social Psychology, University of Padua, via Venezia, 8, Padova, Italy. Electronic mail may be sent to chiara.turati@unipd.it. the ability to discriminate among different exemplars of the face category, recognizing a face as familiar. Thus, such ability capitalizes on recognition memory capabilities, and differs from face detection, which refers to the capacity to discriminate perceptually between face and nonface visual objects, eventually showing a visual preference for the former over the latter. A bulk of studies have investigated face recognition in preschool-aged children (e.g., Sangrigoli & de Schonen, 2004) and infants (e.g., Pascalis, de Haan, Nelson, & de Schonen, 1998), whereas far less concern has been dedicated to the study of face recognition abilities in newborns (see Pascalis & de Schonen, 1994; Pascalis, de Schonen, Morton, Deruelle, & Fabre-Grenet, 1995; Walton, Armstrong, & Bower, 1998). Evidence supporting the claim that not only do newborns differentiate between faces and nonface visual objects but they also process information about individual faces, derives mainly from the observation that, within hours from birth, infants show a visual preference for their mother s face over a female unfamiliar face (Bushnell, 2001; Bushnell, Sai, & Mullin, 1989; Field, Cohen, Garcia, & Greenberg, 1984; Pascalis et al., 1995). These findings indicate that, in real-life situations, newborns are able to learn about a specific individual face to which they are repeatedly exposed within a short time after birth. More specifically, after having learned their mother s face in a multimodal, natural context, newborns show the ability to recognize their mother in a controlled setting, where cues from her smell and her r 2006 by the Society for Research in Child Development, Inc. All rights reserved /2006/

2 298 Turati, Macchi Cassia, Simion, and Leo voice are eliminated and only visual information on face identity is provided (see Bushnell et al., 1989). Newborns ability to recognize their mother s face seems to be the product of a more general capacity to discriminate and recognize individual human faces. Pascalis and de Schonen (1994) demonstrated that, after habituation with a photograph of a stranger s face, 4-day-old infants looked longer at a new face than at the familiar one even after a retention interval of 2 min. This evidence demonstrates that newborns face recognition competencies are observable even when learning takes place in a nonnatural, unimodal, experimental context. Further support for this conclusion comes from studies in which schematic face-like configurations differing in the shape of the inner elements were used (Simion, Farroni, Macchi Cassia, Turati, & Dalla Barba, 2002; Turati & Simion, 2002). Despite its paucity, the available evidence converges to suggest that, at birth, infants are able to acquire and retain some visual information embedded in a face that allows subsequent recognition after a brief retention interval. This early learning capacity is thought to be mediated by a general purpose mechanism (de Schonen, 2002; de Schonen & Mancini, 1995; de Schonen & Mathivet, 1989; Johnson, 1993), as newborns are also able to recognize nonface stimuli to which they have been previously habituated (e.g., Macchi Cassia, Simion, Milani, & Umiltà, 2002; Slater, Morison, & Rose, 1985). However, although the majority of researchers within the field would agree that, from the beginning of life, newborns are capable of learning about individual faces based on experience, it still remains an open question as to what information newborns actually process and encode when they discriminate, learn, and recognize a specific face. This issue appears relevant because many studies within the face recognition developmental literature indicate that, with development, come changes in the perceptual cues that children rely on in order to recognize people s faces. Specifically, the relative importance of the inner and outer features of the face changes with age in relation to the familiarity of the person to be recognized. As for highly familiar or famous faces, there is a transition from a greater reliance on outer features (the hairline) to a greater reliance on inner features (the eyes, nose, and mouth) (Campbell & Tuck, 1995; Campbell, Walker, & Baron-Cohen, 1995; Campbell et al., 1999). Five-to- 6-year-old children are more likely to be able to name their classmates or famous people from seeing just their outer features. At 11 years, there appears to be a reversal in this early pattern of reliance on outer over inner parts for recognition, in that children, as adults, rely more on inner than outer facial features. As for unfamiliar faces, a more stable developmental trend emerges, in that at all ages recognition is easier when it is driven by outer rather than inner facial cues (Newcombe & Lie, 1995; Want, Pascalis, Coleman, & Blades, 2003). Put together, these findings concerning the nature of the perceptual cues driving children s capacity to discriminate and recognize individual faces lead to the prediction that, regardless of the familiarity of the face to be recognized, in the first years of life external rather than internal facial features should play a prominent role. Within the infancy literature, there is evidence that, between 3 and 10 months of age, infants move from processing the internal and external features of a face independently to processing the relationship between them (Cashon & Cohen, 2003). These findings have been interpreted as showing developmental changes in infants capacity to process faces in a configural rather than in an analytical manner, but they do not provide any indication as to whether inner or outer facial features alone are sufficient cues for infants face recognition. This issue has been the focus of a few studies that investigated the value of the two sources of information in producing specific effects, such as the preference for the mother s face (Bartrip, Morton, & de Schonen, 2001; Pascalis et al., 1995) and the socalled attractiveness effect (Slater et al., 2000). Pascalis et al. (1995) demonstrated that newborns preference for the mother s face over that of a female stranger disappeared when the outer contour of the head and hairline were masked and only the inner features of the two faces were visible (i.e., when both women wore scarves around their heads). On the basis of these results, the authors concluded that, in order to recognize and prefer the mother, newborns used the outer features of the face. This conclusion would be consistent with the well-known claim that newborns visual scanning patterns tend to be focalized toward a well-contrasted area corresponding to the external frame (Maurer, 1983; Salapatek, 1968). The presence versus absence of inner and outer features of the mother s face has been systematically manipulated with infants aged days in a more recent study by Bartrip et al. (2001). Data from the whole-face condition indicated a developmental trend from interest in the mother s face in the first 2 months of life, shifting with a simple linear function to a preference for the stranger by 5 months of age. However, when only the internal or external features were visible, infants visual behavior appeared unstable, with the mother s face being preferred over

3 Newborns Face Recognition 299 that of a stranger at days in the internal features condition, and at days in the external features condition. Results provided by this study are not readily interpretable, given the fluctuating profile of the data obtained in the three different conditions. However, together with the findings obtained by Pascalis et al. (1995), this evidence may be interpreted as indicating that infants in their first weeks of life seem to acquire a representation of their mother s face in which both the inner and the outer facial features have an integral part. Whenever one of these two sources of information is removed, the preference that infants show for their mother s face disappears. Apparently, a quite different picture emerges from a study by Slater et al. (2000), which showed that one single source of information, that provided by inner features, is sufficient to induce newborns preference for attractive faces. When pairs of female faces judged by adults as attractive or unattractive are shown to newborns, they look longer at the attractive ones (Slater et al., 1998). Crucially, it has been found that such spontaneous preference is maintained when the external facial features are equated within the pair and only the inner features differ. On the contrary, when identical inner facial features and different external features are shown, the preference vanishes (Slater et al., 2000). The authors interpreted these findings as clear evidence that newborns used information about inner rather than outer facial features in making preferences based on attractiveness. Nevertheless, it should be noted that Slater et al. (2000) used a switched design in which, in order to test the role of inner and outer features, the two sources of information were not selectively removed but rather equated within the pair of faces that was shown to the newborn. Therefore, the evidence provided by Slater et al. s (2000) study does not allow one to draw any conclusion about newborns ability to differentiate a face on the sole basis of the information conveyed by the inner part. To summarize, the available evidence does not depict a consistent and conclusive picture concerning what perceptual cues drive newborns ability to discriminate and recognize individual faces. In fact, evidence is confined to faces of a peculiar nature, such as the mother s face or attractive faces, whose discrimination was tested within the preferential looking paradigm. The use of this paradigm within the studies on newborns preference for the mother s face or attractive faces capitalizes on the extensive experience with faces that newborns acquire in their daily life within a multimodal, natural context. As a consequence, in those studies, the amount and type of experience that leads to the emergence of the observed visual preferences eludes any control. A second drawback of those studies refers to the lack of a systematical manipulation of the presence versus absence of inner and outer facial features, whose role in producing newborns face discrimination has never been directly tested by selectively removing each of the two sources of information. The only study where this manipulation was performed is that by Bartrip et al. (2001), which, however, used mothers faces as stimuli and was run with day-old infants rather than few-day-old newborns. This investigation attempted to surmount these drawbacks by selectively presenting newborns with the inner or the outer parts of real face images in a habituation paradigm with unfamiliar female faces. Habituation is the paradigm usually employed to test infants discrimination and recognition abilities. Crucially, in the current study the use of this paradigm allowed for a strict control of the amount and type of visual experience newborns accumulated with a specific face before being tested for their recognition ability. This was also carried out by using as stimuli unfamiliar faces to which newborns were experimentally familiarized. Experiment 1 In Experiment 1, newborns ability to discriminate and recognize experimentally familiarized images of real faces was tested in three different conditions: when the face was fully visible (full-face condition), when only the inner features were presented (inner features condition), and when the outer features alone were shown (outer features condition). On the basis of what is known about the functional properties of the visual system at birth (Atkinson, 2000), it could be hypothesized that poor visual acuity may prevent newborns from discriminating the inner features of the face, rather allowing the detection of the external features. If this were the case, newborns should manifest face recognition abilities when the whole face is presented (full-face condition), and when only the external features are shown and the internal features are masked (outer features condition). In contrast to this prediction, a neural network simulation study by Valentine and Abdi (2003) suggested that, despite their poor visual acuity, newborns would be able to discriminate a face based exclusively on its inner part. On condition that these indications could be extended to real babies, all the three conditions tested in the current study should

4 300 Turati, Macchi Cassia, Simion, and Leo provide newborns with sufficient information to allow for effective recognition. One final hypothesis is that both inner and outer features of the face play a crucial role in driving newborns face recognition, which should thus be disrupted by the absence of either of the two sources of information. According to this prediction, only newborns tested in the full-face condition should recognize the familiar face to which they have been previously habituated, thus manifesting a preference for the new face. Method Participants. The participants were 66 (40 males) healthy and full-term, 1 3-day-old infants (mean age 5 52 hr, SD 5 8.5) recruited at the maternity ward of the Pediatric Clinic of the University of Padova. They were middle-class infants and 92% of them were Caucasian, 6% African, and 2% Asian. Twentyfour additional infants were tested, but 14 did not complete testing because of fussiness, 7 were excluded from the data analysis because of position preference, and 3 were excluded because of technical problems. Infants were tested only if awake and in an alert state, after the parents gave their informed consent. They were tested in one of three different conditions: full-face condition (N 5 18), inner features condition (N 5 30), and outer features condition (N 5 18). Stimuli. Stimuli were black and white photographs of 6 Caucasian women s faces (aged years) paired into three different pairs. Models were photographed in a frontal pose with a neutral expression under the same lighting conditions. They were asked not to wear glasses or jewelry, and other minor distinctive details (e.g., blemishes or pimples) were digitally removed using the software Adobe Photoshop. The obtained face images were used as stimuli in the full-face condition (see Figure 1). Once presented on the PC monitors, they were 25.5 cm high (about 491). The width varied from a minimum of 18 cm (about 341) to a maximum of 21 cm (about 401) so that the natural proportions of each face were preserved. The six images were then manipulated so as to create two more versions of each face: one in which the outer features (i.e., the hair and ears) were re- Figure 1. Stimuli shown in the habituation and test phases in the full-face, inner features and outer features conditions of Experiment 1.

5 Newborns Face Recognition 301 moved and only the inner portion of the face was visible (inner features condition), and the other in which the inner features were masked so that the inner portion of the face became an undifferentiated homogeneous gray area (Outer features condition; see Figure 1). The dimensions of the stimuli in the outer features condition were identical to those of the stimuli used in the full-face condition. On the contrary, the dimensions of the stimuli used in the inner features condition were smaller, in that the outer portion of the faces was removed and the inner portion was presented in its original dimensions. The face images within this condition were 21 cm (about 401) high and cm wide (from about 241 to about 261). Apparatus. The infant sat on a student s lap, in front of a black panel, at a distance of about 30 cm. The panel had two square holes where the black screens of two computer monitors appeared. The infant s eyes were aligned with a red flickering light emitting diode (LED), located in the center of the screen. The LED was used to attract the infant s gaze at the start of both the habituation and preference test phases, subtended about 21 of a visual angle, and, when turned on, blinked at a rate of 300 ms on and 300 ms off. Stimuli were projected at a distance of 7 cm from the central LED. To prevent interference from irrelevant distractors, peripheral vision was limited by two black panels placed on both sides of the infant. Procedure. As soon as the infant was apparently at ease and his/her gaze was properly aligned with the central flickering LED, the habituation phase was begun by pressing a key on a keyboard. This automatically turned off the central LED and activated the habituation stimuli. During the habituation phase, a face image was projected bilaterally, on each side (i.e., left and right) of the central LED. Bilateral rather than central presentation was chosen for two different reasons. First, when newborns look at a centrally presented stimulus, it is difficult for an observer to decide if they are actually looking at the stimulus or if they simply do not move their eyes from the central position. Second, we wanted to minimize differences in stimulus presentation conditions across habituation and test phases. An observer, naïve to the hypotheses being tested and to the stimuli presented, recorded the duration of each fixation on the stimulus by pressing a push button that was connected to the computer. Because during the habituation phase the same stimulus was presented on the left and on the right, the amount of looking was recorded irrespective of the side. A lookaway criterion of 2 s was used to determine the end of each fixation. In order to be sure that this criterion was strictly respected, the software was planned so that it automatically compacted two consecutive fixations that were not separated by a time interval of at least 2 s. The stimuli remained on the screen until the habituation criterion was reached. The infant was judged to have been habituated when, from the fourth fixation on, the sum of any three consecutive fixations was 50% or less than the total of the first three (Horowitz, Paden, Bhana, & Self, 1972; Slater et al., 1985). Only when the habituation criterion was reached, the stimuli were automatically turned off and the central flickering LED was turned on. As soon as the infant s gaze was realigned to the central LED, a preference test phase started. Each infant was given two paired presentations of the test stimuli. During each presentation, infants were simultaneously presented with two face images, a novel face and the face to which they have been habituated. The two paired stimuli were always shown in both left and right positions, the position being reversed from presentation 1 to presentation 2. The habituation stimulus within each pair of faces was counterbalanced between subjects, and its initial left right position was counterbalanced across subjects. The central LED flickered between the first and the second presentation but did not flicker when the test stimuli were shown. During the preference test phase, the observer, blind to the hypotheses being tested and to the stimuli presented, recorded the duration of an infant s fixations on each stimulus by pressing two different push buttons depending on whether the infant looked at the right or the left position. Each presentation lasted until a total of 20 s of looking to the novel and/or familiar stimuli had been accumulated. All testing sessions were video-recorded. Videotapes of eye movements were subsequently codified by a second observer unaware of the stimuli presented. The mean estimate of reliability between observers was 0.89 (Pearson s correlation), so the recording procedure has to be considered reliable. Newborns were tested in one of three different conditions differing exclusively for the type of stimuli presented. In the full-face condition, newborns were habituated and tested with images of fully visible faces, in the inner features condition infants were shown with the internal region of the same faces, and in the outer features condition newborns were presented with the outer part of the face images (see Figure 1). Within each condition, each of the three pairs of women faces was used equally often.

6 302 Turati, Macchi Cassia, Simion, and Leo Results All infants reached the habituation criterion. A one-way analysis of variance (ANOVA) was run comparing total fixation times to reach the habituation criterion in the three different conditions (full face, inner features, outer features). The comparison was significant, F(2, 63) , po.008, and post hoc t tests showed that newborns total fixation times were significantly lower in the outer features condition (M s, SD ) than in the full-face condition (M s, SD ), t(34) , po.002, and in the inner features condition (M s, SD ), t(46) , po.004. In order to test whether newborns were able to recognize the face image to which they were habituated, a novelty preference score (percentage) was computed. Each infant s looking time at the novel stimulus during the two test presentations was divided by the total looking time to both test stimuli over the two presentations, and subsequently converted into a percentage score. Hence, only scores significantly above 50% indicated a preference for the novel stimulus. Because a preliminary ANOVA revealed that no main effect or interactions involved the factor face pair, for subsequent statistical analyses data were collapsed over this variable. When computed irrespective of the condition to which newborns belonged, the mean novelty preference score was 65.30% (SD ), which significantly differed from the chance level of 50%, t(65) , po.001. This result seems to indicate the presence at birth of the capacity to recognize fully visible faces or portions of these same faces. To determine whether the novelty preference score was significantly different from the chance level of 50% in each of the three conditions, three separate one-sample t tests were applied, one for each condition (see Figure 1). Preference scores for the novel stimulus were significantly above chance for the full-face condition (M %, SD ), t(17) , po.02, the inner features condition (M %, SD ), t(29) , po.03, and the outer features condition (M %, SD ), t(17) , po.001. A one-way ANOVA revealed that the mean novelty preference scores for the three conditions did not differ significantly, F(2, 63) , p4.05. Discussion Overall, the evidence gathered in the present experiment provides a further confirmation that newborns can discriminate and recognize images of fully visible unfamiliar faces to which they have been experimentally familiarized. In addition, our data show that inner and outer facial features alone convey sufficient information in order for face recognition to take place in newborns. These results led to the conclusion that the limited resolution capacities of the visual system at birth do not prevent few-day-old infants from detecting and discriminating the information embedded in the inner portion of the face. This conclusion is supported not only by the finding that newborns were able to recognize the familiar face in the inner features condition, but also by the comparative analysis of newborns looking times during the habituation phase in the three different experimental conditions. Newborns longer habituation time in the full-face and inner features conditions than in the outer features condition may be plausibly interpreted as a consequence of infants exploration and encoding of the inner facial features that are masked in the outer features condition. Yet, evidence gathered in Experiment 1 raises three different issues, which still need to be addressed. First, as noted here above, newborns habituation times were shorter in the outer features condition than in the inner features and full-face conditions. Also, a larger sample was needed in order to reach statistical significance in the inner features condition (N 5 30) as compared with the outer features or the full-face condition (N 5 18). This suggests that, although infants at birth can use both the external portion of the head region and the internal facial features to recognize an individual face, the outer features may be processed more readily than the inner features. This pattern of evidence closely resembles that obtained by Quinn and Eimas (1996, Experiment 8) in a study examining how 3- month-old infants categorize cat versus dog faces based on internal facial features versus external features of the head. Quinn and Eimas s (1996) results hint at the idea that the external features were more readily usable than the internal features, although both cues provided infants with the critical source of information to categorically differentiate cats and dogs. The possibility that outer facial features would require less effort in order to be processed as compared with inner features will be further investigated in Experiment 2, where the effect of the selective removal of either the outer or inner features of a familiarized face on newborns recognition abilities will be tested. A second issue raised by the evidence gathered in Experiment 1 is that, apparently, some of our findings conflict with those reported in the literature.

7 Newborns Face Recognition 303 Specifically, our results seem to contrast with Pascalis et al. s (1995) demonstration of an outer-face advantage in newborns recognition of their mother s face, because they show that newborns face recognition is maintained even when the external features are removed. Indeed, we showed that the presence of only the inner or the outer parts of the face is per se sufficient to produce effective recognition at birth. Moreover, the demonstration that inner features alone can drive newborns face recognition is not in line with the reported developmental transition from a greater reliance on outer features to a greater reliance on inner features in face recognition (Want et al., 2003). In fact, the apparent discrepancy between our results and previous ones can be resolved pointing to a crucial methodological issue. In Experiment 1, newborns had to recognize a familiar face to which they had previously been habituated when no alterations had been made in the perceptual appearance of the face between the learning and the recognition phase. In contrast to that, in the studies in which children s recognition abilities were investigated (e.g., Want et al., 2003) as well as in those in which newborns preference for the mother s face was tested (e.g., Pascalis et al., 1995), participants were asked to recognize the inner or the outer portion of a face that they had previously learned in its entirety. For instance, in Pascalis et al. s (1995) study, after having learned their mother s face in its natural appearance, newborns had to recognize a modified version of the same face, in which the hair was masked by a scarf. Indeed, in this study newborns might have processed both internal and external features of the face in its natural context, but removing the outer features might have disrupted recognition. In other words, newborns might have failed to recognize the new configuration with the external contour masked as the face of the mother that they had previously learned. Therefore, it seems to us that, rather than showing newborns inability to recognize their mother s face based on its inner features, the evidence gathered by Pascalis et al. (1995) revealed newborns failure to accomplish a more demanding task, namely the detection of the perceptual invariance between two appearances of the same facefthe mother s face with and without the hair. This hypothesis appears reasonable in light of recent evidence showing that a modification in the perceptual appearance of the mother s face, produced by the addition of a wig, disrupted newborns preference for their mother (Bushnell, 2003). Together with the data reported by Pascalis et al. (1995), these findings point to the idea that any alteration in the perceptual appearance of a familiar face, produced by either the removal (e.g., Pascalis et al., 1995) or the addition (e.g., Bushnell, 2003) of specific features, would prevent newborns from providing a recognition response. A further purpose of Experiment 2 will be to explore this issue in a controlled setting in which newborns were experimentally habituated to a version of an unfamiliar face (e.g., a full face) and subsequently tested for their ability to recognize a modified version of the same face (e.g., the face without the hair and ears). Finally, data gathered in Experiment 1 leave open the intriguing question of whether newborns in the full-face and inner features conditions relied on local or configural information. This question is crucial to the issue of whether, early in life, face processing is based on analytical visual processing strategies, allowing for the encoding of the local facial features (e.g., eyes, nose, or mouth), or configural strategies, allowing for the encoding of the specific spatial relationships among the features that make each face unique (e.g., the distance between eyes, nose, and mouth; Rhodes, Brake, & Atkinson, 1993). To investigate whether the local or configural aspects of the face are predominant in permitting face recognition at birth, Experiment 3 will test newborns recognition abilities when faces are shown in an inverted orientation. Indeed, in the literature there is a general agreement about the fact that face inversion interferes with configural processing (Maurer, Le Grand, & Mondloch, 2002). Experiment 2 The aim of Experiment 2 was two-fold. First, we sought to determine whether newborns face recognition abilities are maintained when the perceptual appearance of the face to which newborns have been habituated is changed from the habituation to test phase. More specifically, the aim was to investigate whether newborns are able to recognize a face to which they have been previously habituated in its full-face version by relying only on a portion of such a face, and whether habituation to a portion of a face allows newborns to subsequently recognize the full face from which such a portion was extrapolated. Our second purpose was to investigate the hypothesis, raised by Experiment 1, that outer facial features may be processed more readily than inner features, providing a more salient perceptual cue for recognition. We predicted that if the outer features were more salient than the inner features, newborns should maintain their recognition ability whenever the outer features remain visible, whereas recogni-

8 304 Turati, Macchi Cassia, Simion, and Leo tion should disappear whenever the outer features are removed. Method Participants. Participants were 97 healthy and fullterm newborns aged hr (mean age 5 41 hr). They were recruited at the maternity ward of the Pediatric Clinic of the University of Padova and met the screening criteria of normal delivery, a birth weight between 2,550 and 4,000 g, and a 5 min Apgar score above 7. Nine infants were tested, but excluded from the final sample as they did not complete testing because of fussiness (N 5 4), or showed a position bias during the preference test phase (N 5 5). Thus, the final sample included 88 newborns (43 males). The participants were middle-class infants and 89% of them were Caucasian, 7% African, and 4% Asian. Infants were tested only if awake and in an alert state, after their parents gave their informed consent. Sixty-two infants were tested in the inner features condition and 26 infants were tested in the outer features condition. Stimuli. The stimuli were the same as those used in Experiment 1 (see Figure 2). Apparatus and procedure. The apparatus and procedure were identical to those used in Experiment 1, except for one aspect. In Experiment 1, the face or the portion of the face shown to newborns during the habituation phase was presented again during the test phase. In contrast, in Experiment 2 a change was made in the perceptual appearance of the familiar Figure 2. Stimuli shown in the habituation and test phases in the inner features and outer features conditions of Experiment 2.

9 Newborns Face Recognition 305 face when it was presented in the test phase. In the inner features condition, half of the newborns were habituated to the photograph of a full female face and subsequently tested with both the familiar and the novel female faces without the outer features (full face! inner features), whereas the other half were habituated to the inner portion of a face and tested with the familiar and a novel face in their fully visible version (inner features! full face) (Figure 2). In the outer features condition, for half of the infants habituation to a full female face was followed by a test phase in which only the outer features of the familiar and the novel face were visible (full face! outer features), whereas for the other half habituation to a face in which the inner features were removed was followed by a test phase in which both the familiar and the novel faces were fully visible (outer features! full face) (Figure 2). Results As for the habituation phase, a t test for independent samples was applied to compare total fixation times to reach the habituation criterion in the two administered conditions (inner features condition and outer features condition). The comparison reached statistical significance, t(86) , po.03. The average total fixation times were s (SD ) for the inner features condition and s (SD ) for the outer features condition. For neither condition was there a significant difference between the time to reach the habituation criterion when newborns were shown the full face, or only the inner or the outer portion of the face: inner features condition: full face! inner features, M , SD , inner features! full face M , SD , t(60) , p4.05; outer features condition: full-face! outer features, M , SD , outer features! full face, M , SD5 17.1, t(24) , p4.05. As for the test phase, a novelty preference score analogous to that calculated in Experiment 1 was computed for each infant in each condition. In order to determine whether newborns face recognition competencies were preserved when a relevant perceptual modification of the familiar stimulus (absence vs. presence of the outer or inner features) was introduced between the habituation and the test phase, a one-sample t test was performed on the entire set of data, comparing novelty preference scores to the chance level of 50%. The comparison attained statistical significance (M %, SD ), t(87) , po.05. Nevertheless, when data were split into conditions (inner features vs. outer features condition; Figure 2), a multifaceted scenario emerged. Two separate one-sample t tests performed for the two different conditions showed that mean novelty preference scores were significantly above chance in the outer features condition (M %, SD ), t(25) , po.001, but not in the inner features condition (M %, SD ), t(61) , p4.05. A t test for independent samples confirmed that the mean novelty preference scores in the two conditions differed significantly, t (86) , po.003. For neither condition was there a significant difference between the mean novelty preference scores manifested by infants habituated to the full face and the mean novelty preference scores manifested by infants habituated solely to the inner or outer portion of the face: inner features condition: full face! inner features, M , SD , inner features! full face, M , SD , t(60) , p4.05; outer features condition: full face! outer features, M , SD , outer features! full face, M , SD , t(24) , p4.05. Discussion Experiment 2 showed that, when the presence versus absence of the outer features was manipulated between the habituation and the test phase in the inner features condition, newborns failed to recognize the familiar face. In Experiment 1, inner and outer facial features alone conveyed sufficient information in order for newborns face recognition to take place. However, in Experiment 2, newborns failed to use inner features alone as a cue to recognize a female stranger s face that they had previously learned in its entirety, and failed to recognize a face in its entirety after being habituated to its inner features only. These findings shed light on the apparent inconsistency between the findings we obtained in Experiment 1 and those previously reported by Pascalis et al. (1995). Our data support the idea that infants failure to recognize their mother s face when she wore a scarf, as in Pascalis et al. s (1995) study, should not be attributed to infants inability to process the inner facial features per se, but rather to their difficulty in recognizing a perceptual similarity between two stimuli highly different in their appearance, such as a fully visible face and a face lacking in its outer parts. Nevertheless, the presence of a perceptual modification between the familiarized and the test face per se is not sufficient to explain the results obtained in Experiment 2. Indeed, when the modification related to the presence versus absence of the inner

10 306 Turati, Macchi Cassia, Simion, and Leo features, with the outer features maintained invariant, as in the outer features condition, newborns face recognition was preserved. Therefore, newborns were able to recognize a modified version of the familiar face on condition that a salient cue was kept constant. This suggests that, early in life, the outer facial features may deliver more salient information about an individual face than the inner features. Although evidence provided by Experiment 1 demonstrated that newborns can recognize a face based solely on its internal part, findings from Experiment 2 indicated that the outer features enjoy an advantage over the inner features in driving face recognition. Such advantage is likely attributable to the fact that the external features of the face are more attractive to newborns as an object of attention, because of their high contrast, texture, and larger size. The greater salience of this portion of the face may render the outer features easier to encode and store than the inner features, and, in turn, lead to relative prioritization of the outer features in the recognition of the familiarized face. Experiment 3 Experiment 3 was designed to test whether newborns recognition performance in the full-face and inner features conditions of Experiment 1 relied on local or configural information. To pursue this goal, we investigated whether newborns ability to recognize individual faces is affected by the orientation of the facial stimuli. Specifically, we tested whether newborns ability to recognize a full face or a face in which only the outer or the inner features were visible is preserved when the face stimulus is presented inverted, that is rotated through It is well known that, in adults, memory and recognition for faces is disproportionately affected by stimulus inversion as compared with that for other classes of familiar and complex mono-oriented objects, such as houses, airplanes, etc. (e.g., Yin, 1969). Converging behavioral data suggest that this face inversion effect results from the disruption of the configural information embedded in faces (e.g., Bartlett & Searcy, 1993; Leder & Bruce, 2000). An analogue to the inversion effect has been recently documented in 4-month-old infants, who have been shown to process faces in a recognition task differently according to whether the stimuli are presented upright or inverted (Turati, Sangrigoli, Ruel, & de Schonen, 2004). Moreover, it has been shown that stimulus inversion disrupts newborns preference for attractive over unattractive face ( attractiveness effect, Slater et al., 2000). The design of Experiment 3 was identical to that of Experiment 1 except for the orientation of the stimuli, which have been presented 1801 rotated. Newborns recognition abilities have been tested in the same three conditions used in Experiment 1: full face, inner features, and outer features. We advanced three different hypotheses. First, if newborns recognition in Experiment 1 was conveyed by local information, the results of Experiment 3 should parallel those of Experiment 1, in that stimulus inversion is known not to impair local processing. Thus, in Experiment 3 face recognition should be observed in all three tested conditions. Alternatively, if newborns face recognition in the full-face and inner features conditions of Experiment 1 relied on configural processing, we expected to observe in Experiment 3 a failure in recognizing the familiarized face in the full-face and inner features conditions, but not in the outer features condition. Finally, a third hypothesis predicted that if configural face processing is at work but the outer features of the face are a particularly salient cue to newborns, the presence of this cue should permit recognition in both the full-face and the outer features conditions. In contrast, face recognition should be absent only in the inner features condition, where the outer features of the face are not visible. Method Participants. The final sample was composed of 70 (36 males) healthy, full-term newborns aged hr (mean age 5 38 hr), tested only if awake and in an alert state. They were middle-class infants and 87% of them were Caucasian, 9% African, and 4% Asian. Eight additional infants were tested but excluded from the final sample because of a position bias during the preference test phase (N 5 6), a technical error (N 5 1), or because they did not complete testing because of fussiness (N 5 1). As in Experiment 1, infants were tested in one of three different conditions: full-face condition (N 5 20), inner features condition (N 5 30), and outer features condition (N 5 20). The number of infants tested in each of the three conditions of the current experiment was paired to (inner features condition) or slightly greater than (outer features and full-face condition) the number of infants tested in the three conditions of Experiment 1, so that any possible difference between the results of Experiments 1 and 3 could not be interpreted as due to a difference in sample size. Stimuli. The stimuli were the same as those used in Experiment 1, with the only exception that they were presented 1801 rotated (see Figure 3).

11 Newborns Face Recognition 307 Figure 3. Stimuli shown in the habituation and test phases in the full-face, inner features, and outer features conditions of Experiment 3. Apparatus and procedure. The apparatus and procedure were identical to those used in Experiment 1. Results A one-way ANOVA was run comparing total fixation times to reach the habituation criterion in the three different conditions (full face, inner features, and outer features). The comparison was significant, F(2, 69) , po.05, and post hoc t tests showed that newborns total fixation times were significantly shorter in the full-face condition (M s, SD ) than in the outer features condition (M s, SD ), t(38) , po.02, and the inner features condition (M s, SD ), t(48) , po.04. These two latter conditions did not differ one from the other, t(48) , p4.05. As for the test phase, a novelty preference score analogous to that calculated in Experiment 1 and 2 was computed for each infant in each condition. A one-sample t test performed on the entire set of data showed that novelty preference scores were significantly above the chance level of 50% (M %, SD ), t(69) , po.002. To determine whether newborns were able to recognize the familiarized face in each of the three tested conditions, three separate one-sample t tests were applied, one for each condition (Figure 3). Preference scores significantly differed from the chance level in the fullface (M %, SD ), t(19) , po.04, and the outer features condition (M %, SD ), t(19) , po.001. In contrast, preference scores in the inner features condition approximated 50% (M %, SD ), t(29) , p4.05, thus indicating that, in this condition, newborns did not manifest the ability to recognize the familiarized face. A one-way ANOVA, F (2, 69) , po.001, revealed that the outer features condition significantly differed from both the full-face, t(38) , po.02, and the inner features condition, t(48) , po.001. The comparison between these two latter conditions approximated, but did not reach statistical significance, t(48) , p4.05. Discussion Inversion of the face stimuli differentially affected newborns recognition performance in the three

12 308 Turati, Macchi Cassia, Simion, and Leo examined conditions. When presented solely with the inner portion of an inverted face, newborns were unable to recognize the familiarized face, as inferred by the lack of preference for the novel face in the inner features condition. Rather, such recognition ability was present in the full-face and outer features conditions. The lack of recognition response observed in the inner features condition strongly suggests that configural processing played a major role in driving newborns recognition performance in the inner features condition of Experiment 1, where faces were presented in their canonical, upright orientation. Apparently, this same conclusion cannot apply to the full-face condition of Experiment 1, in that inversion in Experiment 3 did not disrupt recognition in the same condition. However, it is worth noting that, in Experiment 3, the mean novelty preference score in the full-face condition (M ), albeit significantly above chance, was also significantly lower than the preference score obtained in the outer features condition (M ). This likely suggests that, although a novelty preference was present in both conditions, recognition was harder in the full-face condition compared with the outer features condition, possibly because of the impairing effects produced by inversion on the processing of the inner portion of the face, that is the portion that, in the inner features condition, was not successfully recognized by newborns. If this were the case, then it can be inferred that configural processing was involved not only in the inner features condition of Experiment 1 but also in the full-face condition of the same experiment. At the same time, however, the fact that recognition was possible when an inverted full face was shown to newborns in Experiment 3 likely indicates that salient perceptual cues embedded in the external portion of the face preserved newborns ability to recognize a canonical face even though inverted. Indeed, the condition that appeared to be less affected by stimulus inversion in Experiment 3 was the one in which only the external features were presented, again suggesting that the outer features condition of Experiment 1 was the only one in which configural processing was not at all involved. This claim is further supported by the pattern of data observed for the habituation phase in the three conditions of Experiments 1 and 3. Newborns looking times to habituate in the outer features condition of the two experiments were almost comparable (Exp. 1 M s vs. Exp. 3 M s). On the contrary, a comparison between habituation times in the two other conditions shows that the inversion of the stimuli in Experiment 3 caused a drop in the fixation times required to reach the habituation criterion in both the full-face (Exp. 1 M s vs. Exp. 3 M s) and inner features conditions (Exp. 1 M s vs. Exp. 3 M s). Again, this suggests that inversion mostly affected newborns processing of the inner portion of the face, which is present in both the full-face and the inner features conditions, rather than the processing of the outer features of the face. General Discussion and Conclusion The general purpose of the present study was to determine what information newborns process and encode when they discriminate, learn, and recognize individual faces. Evidence from Experiment 1 demonstrated that either the inner or outer features of the face can act as sufficient cues for face recognition. In particular, findings showed that, contrary to what has been previously claimed (Pascalis et al., 1995), already at birth inner features alone convey enough information in order for face recognition to take place. However, although these outcomes indicate that the outer features are not the only source of information used at birth to recognize individual faces, data from Experiment 2 point to the presence of an outer-face advantage in newborns face recognition. When the external features of the familiarized face were removed, newborns failed to show recognition. On the contrary, the removal of the inner region of the face did not prevent recognition. Together, these findings indicate that, although either the internal or external features of the face are usable for recognition, the latter provide newborns with a more salient perceptual cue as compared with the inner facial features. This outcome is in line with the prediction, derived from studies on children s face recognition abilities (Campbell et al., 1999; Want et al., 2003), that, early in development, external rather than internal facial features may play a prominent, although not exclusive, role in driving face recognition. In newborns, the salience of the external features of the face likely derives from their peculiar perceptual characteristics (e.g., contrast, size, texture), which optimally match the functional properties of the newborns visual system. A further conclusion that may be drawn from Experiment 2 is that not only are newborns capable of detecting, encoding, and recognizing both the inner and the outer portion of the face when presented in isolation, as shown by Experiment 1, but they are also sensitive to the relations between these