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This study investigated the difference in the McGurk effect between own-race-face and other-race-face stimuli among Japanese infants from 5 to 9 months of age. The McGurk effect results from infants using information from a speaker’s face in audiovisual speech integration. We hypothesized that the McGurk effect varies with the speaker’s race because of the other-race effect, which indicates an advantage for own-race faces in our face processing system. Experiment 1 demonstrated the other-race effect on audiovisual speech integration such that the infants ages 5–6 months and 8–9 months are likely to perceive the McGurk effect when observing an own-race-face speaker, but not when observing an other-race-face speaker. Experiment 2 found the other-race effect on audiovisual speech integration regardless of irrelevant speech identity cues. Experiment 3 confirmed the infants’ ability to differentiate two auditory syllables. These results showed that infants are likely to integrate voice with an own-race-face, but not with an other-race-face. This implies the role of experiences with own-race-faces in the development of audiovisual speech integration. Our findings also contribute to the discussion of whether perceptual narrowing is a modality-general, pan-sensory process.

Pupil contagion is the phenomenon in which an observer’s pupil-diameter changes in response to another person’s pupil. Even chimpanzees and infants in early development stages show pupil contagion. This study investigated whether dynamic changes in pupil diameter would induce changes in infants’ pupil diameter. We also investigated pupil contagion in the context of different faces. We measured the pupil-diameter of 50 five- to six-month-old infants in response to changes in the pupil diameter (dilating/constricting) of upright and inverted faces. The results showed that (1) in the upright presentation condition, dilating the pupil diameter induced a change in the infants’ pupil diameter while constricting the pupil diameter did not induce a change, and (2) pupil contagion occurred only in the upright face presentation, and not in the inverted face presentation. These results indicate the face-inversion effect in infants’ pupil contagion.

Previous functional neuroimaging studies imply a crucial role of the superior temporal regions (e.g., superior temporal sulcus: STS) for processing of dynamic faces and bodies. However, little is known about the cortical processing of moving faces and bodies in infancy. The current study used functional near-infrared spectroscopy (fNIRS) to directly compare cortical hemodynamic responses to dynamic faces (videos of approaching people with blurred bodies) and dynamic bodies (videos of approaching people with blurred faces) in infants' brain. We also examined the body-inversion effect in 5- to 8-month-old infants using hemodynamic responses as a measure. We found significant brain activity for the dynamic faces and bodies in the superior area of bilateral temporal cortices in both 5- to 6-month-old and 7- to 8-month-old infants. The hemodynamic responses to dynamic faces occurred across a broader area of cortex in 7- to 8-month-olds than in 5- to 6-month-olds, but we did not find a developmental change for dynamic bodies. There was no significant activation when the stimuli were presented upside down, indicating that these activation patterns did not result from the low-level visual properties of dynamic faces and bodies. Additionally, we found that the superior temporal regions showed a body inversion effect in infants aged over 5 months: the upright dynamic body stimuli induced stronger activation compared to the inverted stimuli. The most important contribution of the present study is that we identified cortical areas responsive to dynamic bodies and faces in two groups of infants (5-6-months and 7-8-months of age) and we found different developmental trends for the processing of bodies and faces.

Significance Recent studies in neuroscience suggest that visual perception is not processed by the purely feed-forward system but by the interaction of forward, horizontal, and feedback processing called recurrent loops. The present study examined the development of recurrent processing using visual backward masking, a perceptual phenomenon in which a visual stimulus is rendered invisible by a mask that follows the stimulus, possibly because of the disruption of recurrent processing. We showed that backward masking is ineffective for infants under 7 mo of age and that they can perceive masked objects that older infants cannot see because of masking. These results suggest that recurrent processing is immature in early infancy and that the mechanisms of visual perception drastically change around this age., Recurrent loops in the visual cortex play a critical role in visual perception, which is likely not mediated by purely feed-forward pathways. However, the development of recurrent loops is poorly understood. The role of recurrent processing has been studied using visual backward masking, a perceptual phenomenon in which a visual stimulus is rendered invisible by a following mask, possibly because of the disruption of recurrent processing. Anatomical studies have reported that recurrent pathways are immature in early infancy. This raises the possibility that younger infants process visual information mainly in a feed-forward manner, and thus, they might be able to perceive visual stimuli that adults cannot see because of backward masking. Here, we show that infants under 7 mo of age are immune to visual backward masking and that masked stimuli remain visible to younger infants while older infants cannot perceive them. These results suggest that recurrent processing is immature in infants under 7 mo and that they are able to perceive objects even without recurrent processing. Our findings indicate that the algorithm for visual perception drastically changes in the second half of the first year of life.

Little is known about the time of development of binocular suppression. In the present study, we evaluated the emergence of binocular suppression in infants by using continuous flash suppression (CFS, Tsuchiya and Koch, 2005). In our experiment, one eye of infants was presented with a static face image at one side of the screen, while another eye was presented with dynamic Mondrian patterns in full screen. Adult observers confirmed that the static face image was consciously repressed by the changing Mondrian patterns. If binocular suppression was functional, the infants would not perceive the face and thus would not show any preference in the experiment. However, if binocular suppression in the infants was not yet acquired, they would perceive the face and the Mondrian patterns at the same time and would thus show preference for the side where the face was presented. The results showed that infants aged 2-3 months, but not those aged 4-5 months, detected the position of the face. Furthermore, this detection was not due to weak contrast sensitivity to the dynamic Mondrian mask. These results indicated that the immature binocular visual system may perceive different images from different eyes simultaneously and that infants may lose this ability after establishing binocular suppression at 4-5 months of age.

Previous studies have revealed perceptual narrowing for the own-race-face in face discrimination, but this phenomenon is poorly understood in face and voice integration. We focused on infants’ brain responses to the McGurk effect to examine whether the other-race effect occurs in the activation patterns. In Experiment 1, we conducted fNIRS measurements to find the presence of a mapping of the McGurk effect in Japanese 8- to 9-month-old infants and to examine the difference between the activation patterns in response to own-race-face and other-race-face stimuli. We used two race-face conditions, own-race-face (East Asian) and other-race-face (Caucasian), each of which contained audiovisual-matched and McGurk-type stimuli. While the infants (N = 34) were observing each speech stimulus for each race, we measured cerebral hemoglobin concentrations in bilateral temporal brain regions. The results showed that in the own-race-face condition, audiovisual-matched stimuli induced the activation of the left temporal region, and the McGurk stimuli induced the activation of the bilateral temporal regions. No significant activations were found in the other-race-face condition. These results mean that the McGurk effect occurred only in the own-race-face condition. In Experiment 2, we used a familiarization/novelty preference procedure to confirm that the infants (N = 28) could perceive the McGurk effect in the own-race-face condition but not that of the other-race-face. The behavioral data supported the results of the fNIRS data, implying the presence of narrowing for the own-race face in the McGurk effect. These results suggest that narrowing of the McGurk effect may be involved in the development of relatively high-order processing, such as face-to-face communication with people surrounding the infant. We discuss the hypothesis that perceptual narrowing is a modality-general, pan-sensory process.

Primary cognitive processes, such as spatial attention, are essential to our higher cognitive abilities and develop dramatically in the first year of life. The spatial aspect of infants' working memory is equivalent to that of adults. However, it is unclear whether this is true for the temporal domain. Thus, we investigated the temporal aspect of infants' working memory using an attentionally demanding task by focusing on the attentional blink effect, in which the identification of the second of the two brief targets is impaired when inter-target lags are short. We argue that finding a similar pattern of the attentional blink in preverbal infants and adults indicates that infants can complete the consolidation of the first target into working memory at a similar temporal scale as adults. In this experiment, we presented 7- to 8-month-old infants with rapid serial visual streams at a rate of 100 ms/item, including two female faces as targets, and examined whether they could identify the targets by measuring their preference to novel faces compared to targets. The temporal separation between the two targets was 200 or 800 ms. We found that the infants could identify both targets under the longer lag, but they failed to identify the second target under the shorter lag. The adult experiment using the same temporal separation as in the infant experiment revealed the attentional blink effect. These results suggest that 7- to 8-month-old infants can consolidate two items into working memory by 800 ms but not by 200 ms.

In this study, we created composite faces using mothers' faces to examine holistic face processing in infants aged 5-8 months. The composite-face effect occurred only in infants aged 7-8 months, suggesting that infants older than 7 months are able to process familiar faces holistically.

Recognition of facial identity and facial expression have been reported to be correlated. Previous studies using static facial photographs reported that identity recognition was not interfered by task-irrelevant change of facial expression but that expression recognition was interfered by task-irrelevant change of facial identity. In this study, we created dynamic morphing animations that simultaneously changes facial identity and expression to investigate the interaction between identity and expression recognition. We tested 7 –8-month-old infants who were around the age at which the recognition of facial expression develops. Using the familiarization–novelty preference procedure, we examined whether infants could learn identity and facial expression from morphing animation. We found that infants learned identity but not expression from the morphing animation. Our results demonstrate that the interaction between identity and expression occurs differently in infancy than in adults when both the di...

Infants less than 1 year old are known to preferentially look at pictures of motion illusion induced by luminance gradation. However, the mechanisms underlying infant’s perception of motion illusion remain unclear. The current study analyzed the eye movement patterns of infants perceiving a motion illusion induced by stationary luminance gradations (a derivative of the Fraser-Wilcox illusion). Infants produced the same movement patterns that increase the magnitude of illusory motion in adults. We conclude that infants and adults similarly perceive motion illusion.

Sound symbolism, which is the systematic and non-arbitrary link between a word and its meaning, has been suggested to bootstrap language acquisition in infants. However, it is unclear how sound symbolism is processed in the infants’ brain. To address this issue, we investigated the cortical response in 11-month-old infants in relation to sound-symbolic correspondences using near-infrared spectroscopy (NIRS). Two types of stimuli were presented: a novel visual stimulus (e.g., a round shape) followed by a novel auditory stimulus that either sound-symbolically matched (moma) or mismatched (kipi) the shape. We found a significant hemodynamic increase in the right temporal area, when the sound and the referent sound were symbolically matched, but this effect was limited to the moma stimulus. The anatomical locus corresponds to the right posterior superior temporal sulcus (rSTS), which is thought to process sound symbolism in adults. These findings suggest that prelinguistic infants have the biological basis to detect cross-modal correspondences between word sounds and visual referents.

Yawning is contagious in human adults. While infants do not show contagious yawning, it remains unclear whether infants perceive yawning in the same manner as other facial expressions of emotion. We addressed this problem using functional near-infrared spectroscopy (fNIRS) and behavioural experiments. We confirmed behaviourally that infants could discriminate between yawning and unfamiliar mouth movements. Furthermore, we found that the hemodynamic response of infants to a yawning movement was greater than that to mouth movement, similarly to the observations in adult fMRI study. These results suggest that the neural mechanisms underlying yawning movement perception have developed in advance of the development of contagious yawning.

Perceiving and judging food quality is indispensable in daily life. The present study examined this ability’s development in infants during the early postnatal months. We tested if infants aged 5–8 months can discriminate different degree of freshness in cabbage, strawberry, carrot, and spinach. In Experiment 1, images of fresh and degraded vegetables were presented side by side; infants aged 7–8 months significantly preferred fresh over degraded cabbage images. In Experiments 2 and 3, infants aged 7–8 months maintained their preference when the images were achromatic, but no longer preferred the fresh cabbage images when pixels in those images were randomized. Given these results, we suggest that the ability to discriminate different degrees of freshness, at least for cabbage, develops at approximately 7–8 months of age, which is the time probably prior to taste learning.

Shadows are powerful cues in the perception of shapes. We can perceive shading and cast shadow implicitly. We investigated infants' ability to detect a single discrepant figure that was depicted by shading or cast shadow and examined the influence of the contrast polarity of shadows on this process. In Experiment 1, we manipulated the blur direction of a shadow to create stimuli that appeared either to be partially shaded or to cast a shadow and then used a preference to test whether this difference would allow 5- to 8-month-old infants to discriminate the figures that adults were able to perceive as different shapes. Only 7- to-8-month-old infants could differentiate one shading figure from cast shadow figures, and vice versa. In Experiment 2, we reversed the contrast polarity of the figure (dark object with a light shadow) and tested whether discrimination was affected. As has been found with adults, infants exposed to this condition were unable to discriminate the contrast-reversed shading and cast shadow figures. Our results suggested that an age of around 7 months is important for development of the ability to perceive shape differences from shading and cast shadows.

Perceptual color space is continuous; however, we tend to divide it into only a small number of categories. It is unclear whether categorical color perception is obtained solely through the development of the visual system or whether it is affected by language acquisition. To address this issue, we recruited prelinguistic infants (5- to 7-mo-olds) to measure changes in brain activity in relation to categorical color differences by using near-infrared spectroscopy (NIRS). We presented two sets of geometric figures to infants: One set altered in color between green and blue, and the other set altered between two different shades of green. We found a significant increase in hemodynamic responses during the between-category alternations, but not during the within-category alternations. These differences in hemodynamic response based on categorical relationship were observed only in the bilateral occipitotemporal regions, and not in the occipital region. We confirmed that categorical color differences yield behavioral differences in infants. We also observed comparable hemodynamic responses to categorical color differences in adults. The present study provided the first evidence, to our knowledge, that colors of different categories are represented differently in the visual cortex of prelinguistic infants, which implies that color categories may develop independently before language acquisition.

Material perception is facilitated by multisensory interactions that enable us to associate the visual properties of a material with its auditory properties. Such interactions develop during infancy and are assumed to depend on the familiarity of materials. Here, we aimed to pinpoint the age at which infants acquire multisensory interactions for the perception of water, which is a familiar material to them. We presented two side-by-side movies of pouring water and ice while providing the corresponding sounds of water and ice, as well as silence. We found that infants older than 5 months of age looked longer at the water movie when they heard the sound of water. Conversely, they did not look at the ice movie when they heard the sound of ice. These results indicate that at approximately 5 months of age, infants develop multisensory interactions between auditory and visual properties of water, but not of ice. The contrasting results between water and ice suggest that the development of multisensory material perception depends on the frequency of interactions with materials during infancy.

Motion direction of a large high-contrast pattern is more difficult to perceive than that of a small one [1]. This counterintuitive perceptual phenomenon is considered to reflect surround suppression, a receptive field property observed in the visual cortex [2-5]. Here, we demonstrate that this phenomenon can be observed in human infants. Infants at 7-8 months of age showed higher sensitivity for a small motion stimulus than for a large one. However, infants under 6 months showed the opposite result; motion sensitivity was higher for a large stimulus. These results suggest that suppressive surround regions beyond classical receptive fields develop in the second half of the first year. Moreover, we examined the size of receptive fields in infants using this phenomenon and found that the center region of receptive fields shrinks from 3 months to 8 months. Our findings suggest that receptive fields related to motion processing are broad and do not have extra-classical receptive fields in early infancy, and that they become narrower and acquire suppressive surround regions in the first year of life.

Our visual system can rapidly process stimuli relevant to our current behavioral goal within various irrelevant stimuli in natural scenes. This ability to detect and identify target stimuli during non target stimuli has been mainly studied in adults, so that the development of this high-level visual function has been unknown among infants, although it has been shown that 15-month-olds' temporal thresholds of face visibility are close to those of adults. However, we demonstrate here that infants younger than 15 months can identify a target face among nontarget but meaningful scene images. In the current study, we investigated infants' ability to detect and identify a face in a rapid serial visual presentation. Experiment 1 examined whether 5- to 8-month-olds could discriminate the difference in the presentation duration of visual streams (100 vs. 11 ms). Results showed that 7- and 8-month olds successfully discriminated between the presentation durations. In Experiment 2, we examined whether 5- to 8-month-olds could detect the face presented for 100 ms and found that 7- and 8-month-olds could detect the face embedded in rapid serial visual streams. To further clarify the face processing at this age of infants, we tested whether infants could identify upright and inverted faces in rapid visual streams in Experiments 3a and 3b. The results showed that 7- and 8-month-olds identified upright faces, but not inverted faces, during the visual stream, which reflected face inversion effects. Overall, we suggest that the temporal speed of face processing at 7 and 8 months of age would be comparable to that of adults. (C) 2019 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

This study examined the development of ability to recognize familiar face in drawings in infants aged 6-8 months. In Experiment 1, we investigated infants' recognition of their mothers' faces by testing their visual preference for their mother's face over a stranger's face under three conditions: photographs, cartoons produced by online software that simplifies and enhances the contours of facial features of line drawings, and veridical line drawings. We found that 7- and 8-month-old infants showed a significant preference for their mother's face in photographs and cartoons, but not in veridical line drawings. In contrast, 6-month-old infants preferred their mother's face only in photographs. In Experiment 2, we investigated a visual preference for an upright face over an inverted face for cartoons and veridical line drawings in 6- to 8-month-old infants, finding that infants aged older than 6 months showed the inversion effect in face preference in both cartoons and veridical line drawings. Our results imply that the ability to utilize the enhanced information of a face to recognize familiar faces may develop aged around 7 months of age.

View-invariant face processing emerges early in life. A previous study (Nakato et al., 2009) measured infant hemodynamic responses to faces from the frontal and profile views in the bilateral temporal areas, which have been reported to be involved in face processing using near-infrared spectroscopy. It was reported that 5-month-old infants showed increased oxyhemoglobin (oxy-Hb) responses to frontal faces, but not to profile faces. In contrast, 8-month-old infants displayed increased oxy-Hb responses to profile faces as well as to frontal faces. In this study, we used the experimental method developed in the previous study to investigate the development of view-invariant face processing, every month for 5 months (from the first 3–8 months of life). We longitudinally measured hemodynamic responses to faces from the frontal and profile views in 14 infants. The longitudinal measurements allowed us to investigate individual differences in each participant. We modeled each infant's hemodynamic oxy-Hb responses to frontal and profile faces using linear regression analysis. Processing of profile faces emerged later and underwent larger improvements than that of frontal faces. We also found an anticorrelation between the speed of improvement in face processing and the hemodynamic response to faces at the age of 3- months. Group analysis of the averaged hemodynamic data from the 14 infants using linear regression revealed that the processing of profile faces emerged between 5 and 6 months of age. Infant view-invariant face processing developed first for frontal faces. This was followed by the emergence of processing of profile faces.

The human perceptual system enables us to extract visual properties of an object’s material from auditory information. In monkeys, the neural basis underlying such multisensory association develops through experience of exposure to a material; material information could be processed in the posterior inferior temporal cortex, progressively from the high-order visual areas. In humans, however, the development of this neural representation remains poorly understood. Here, we demonstrated for the first time the presence of a mapping of the auditory material property with visual material (“Metal” and “Wood”) in the right temporal region in preverbal 4- to 8-month-old infants, using near-infrared spectroscopy (NIRS). Furthermore, we found that infants acquired the audio-visual mapping for a property of the “Metal” material later than for the “Wood” material, since infants form the visual property of “Metal” material after approximately 6 months of age. These findings indicate that multisensory processing of material information induces the activation of brain areas related to sound symbolism. Our findings also indicate that the material’s familiarity might facilitate the development of multisensory processing during the first year of life.

We examined whether infants aged 6-8 months show object-based attention using the preferential looking method. In object-based attention, which is a prerequisite function for efficient real-world processing of various stimuli, a target that appears at a cued object is detected and processed faster than a target appearing at an uncued object. We presented 6- to 8-month-old infants with the visual stimuli consisting of two white vertical rectangles side by side, in which a target appearing at 1) the cued location, 2) the end opposite to the cued location, and 3) another rectangle's end following the cue, using an established paradigm, and measured each infant's first saccade to the target. We found that (1) infants of all ages could make the first saccade to the target appearing at the cued location, (2) only 8-month-old infants made the first saccade to the target appearing at the opposite end to the cued location more accurately than to the target appearing at the other rectangle's end. These results indicate that object-based attention might be acquired around 8 months compared with the spatial cueing effect that appears at around 6 months. Our findings suggest that the objects play a role in visual attention in 8-month-old infants.

When humans perceive the lightness of an object's surface in shadows there is an implicit assumption that cast shadows dim the surface. In two experiments, we investigated whether 5- to 8-month-old infants make this assumption about shadows. According to this shadow assumption, the apparent change in lightness produced by shadows on an object's surface are attributed to blocked light sources. If infants can use the shadow assumption to perceive the object's lightness in shadows, they will also be able to detect unnatural lightness changes in shadows. We compared the infants' looking times to the unnatural and the natural lightness changes in the shadow when an object (duck) goes through the cast shadow. In Experiment 1, we examined whether infants could detect the unnatural lightness changes of the object's surface in shadows. We created computer-graphic movies of unnatural and natural lightness changes to the duck's surface. Our results showed that 7- to 8-month-olds but not 5- to 6-month-olds significantly preferred the movie with the unnatural changes in lightness, indicating that only the older infants could detect these changes. In Experiment 2, we confirmed that the infants' preference was based on the detection of unnatural lightness changes according to the shadow assumption. The natural and the unnatural lightness changes of Experiment 1 were presented without cast shadows. Under these conditions, neither younger nor older infants showed a significant preference. Taken together, the experiments showed that 7- to 8-month-old infants could detect the unnaturalness of a surface's lightness changes produced by shadows. In conclusion, our findings suggest that 7- to 8-month-old infants can perceive an object's lightness in shadows by using an assumption that cast shadows dim the surface of an object.

To examine sensitivity to pictorial depth cues in young infants (4 and 5 months-of-age), we compared monocular and binocular preferential looking to a display on which two faces were equidistantly presented and one was larger than the other, depicting depth from the size of human faces. Because human faces vary little in size, the correlation between retinal size and distance can provide depth information. As a result, adults perceive a larger face as closer than a smaller one. Although binocular information for depth provided information that the faces in our display were equidistant, under monocular viewing, no such information was provided. Rather, the size of the faces indicated that one was closer than the other. Infants are known to look longer at apparently closer objects. Therefore, we hypothesized that infants would look longer at a larger face in the monocular than in the binocular condition if they perceived depth from the size of human faces. Because the displays were identical in the two conditions, any difference in looking-behavior between monocular and binocular viewing indicated sensitivity to depth information. Results showed that 5-month-old infants preferred the larger, apparently closer, face in the monocular condition compared to the binocular condition when static displays were presented. In addition, when presented with a dynamic display, 4-month-old infants showed a stronger ‘closer’ preference in the monocular condition compared to the binocular condition. This was not the case when the faces were inverted. These results suggest that even 4-month-old infants respond to depth information from a depth cue that may require learning, the size of faces.

Infants' ability to recognize uncanny human faces increases during the first year of life. In turn, their ability to recognize faces of other species declines at almost the same period (perceptual narrowing). In the current study, we aimed to clarify the relationship between the perception of uncanniness of faces and perceptual narrowing in infants and adults. We used the “uncanny valley task,” in which the participants were required to discriminate the faces of humans and monkeys by different eye size. Results showed that 3- to 5-month-old infants could not discriminate either monkey or human faces by eye size, whereas 6- to 8-month olds could. Adults showed higher discrimination performance for human than monkey faces and perceived the human faces with extremely large or small eyes as exceedingly eerie. Our results suggest that perception of uncanniness of faces is formed after perceptual narrowing.

We aimed to verify painters' empirical rules in painting portraits from the perspective of face perception. In particular, we examined the effects of lighting on perceiving impressions and facial expressions of a depicted person by using portrait paintings with various lighting conditions of contrast (high, low) and position (left, right). Viewers rated their impressions of the people in the portraits and those people's expressions using 7-point scales. Impressions regarding likability or attractiveness were stable regardless of the lighting conditions, while the other impressions differed among the lighting conditions. Positive emotions were perceived more strongly in paintings with low contrast, whereas negative emotions were perceived more strongly in paintings with high contrast. Overall, these results suggest that lighting has a systematic effect on face perception even in portrait paintings. We propose that the current study provides empirical evidence of painters' implicit knowledge.

The aim of the current study is to reveal the effect of global linear transformations (shearing, horizontal stretching, and vertical stretching) on the recognition of familiar faces (e.g., a mother's face) in 6- to 7-month-old infants. In this experiment, we applied the global linear transformations to both the infants’ own mother's face and to a stranger's face, and we tested infants’ preference between these faces. We found that only 7-month-old infants maintained preference for their own mother's face during the presentation of vertical stretching, while the preference for the mother's face disappeared during the presentation of shearing or horizontal stretching. These findings suggest that 7-month-old infants might not recognize faces based on calculating the absolute distance between facial features, and that the vertical dimension of facial features might be more related to infants’ face recognition rather than the horizontal dimension.

Facial movement facilitates the recognition of facial expressions. While an intense expression is expressive enough to be recognized in a still image, a subtle expression can be recognized only in motion (Ambadar, Schooler, & Cohn, 2005, Psychological Science, 16, 403–410). The present study investigated whether infants recognize a subtle expression, and whether facial movement facilitates infants' recognition of a subtle expression. In experiment 1 4- to 7-month-old infants were tested for their spontaneous preference for a happy subtle expression rather than a neutral face, but they did not show a spontaneous preference. To confirm that infants did not recognize the static subtle expression, we conducted experiment 2 using the familiarization-novelty procedure. Infants were first familiarized with a static subtle happy expression. Following familiarization, they were presented with a pair of peak expressions of happiness and anger, but showed no significant novelty preference. In experiment 3 we presented the subtle expression dynamically. Infants were familiarized with a dynamic subtle expression and were tested for their novelty preference. The 6- to 7-month-olds showed a significant novelty preference, while 4- to 5-month-olds did not. These results suggest that infants can recognize the subtle expression only in dynamic presentation and that facial movement facilitates infants' recognition of facial expression.

Human can easily detect other's eyes and gaze from early in life. Such sensitivity is supported by the contrast polarity of human eyes, which have a white sclera contrasting with the darker colored iris (Kobayashi & Kohshima, (1997). Nature, 387, 767-768; Kobayashi & Kohshima, (2001). Journal of Human Evolution, 40, 419-435). Recent studies suggest that the contrast polarity around the eyes plays an important role in infants' face processing. Newborns preferred upright face images to inverted ones in contrast-preserved faces, but not in contrast-reversed faces (Farroni et al., (2005). Proceedings of National Academy of Sciences of the United States of America, 102, p. 17245-17250). Seven- to 8-month-old infants failed to discriminate between faces when the contrast polarity of eyes was reversed (Otsuka et al., (2013). Journal of Experimental Child Psychology, 115, 598-606). Neuroimaging study with adults revealed that full-negative faces induced less activation in the right fusiform gyrus than either full-positive faces or negative faces with contrast-preserved eyes (Gilad et al., (2009). Proceedings of National Academy of Sciences of the United States of America, 106, p. 5353-5358). In the present study, we investigated whether contrast-reversed eyes diminish infants' brain activity related to face processing. We measured hemodynamic responses in the bilateral temporal area of 5- to 6-month-old infants. Their hemodynamic responses to faces with positive eyes and those with negative eyes were compared against the baseline activation during the presentation of object images. We found that the presentation of faces with positive eyes increased the concentration of oxy-Hb in the right temporal area and those of total-Hb in the bilateral temporal areas. No such change occurred for faces with negative eyes. Our results suggest the importance of contrast polarity of the eyes in the face-selective neural responses from early development.

Just as faces share the same basic arrangement of features, with two eyes above a nose above a mouth, human eyes all share the same basic contrast polarity relations, with a sclera lighter than an iris and a pupil, and this is unique among primates. The current study examined whether this bright–dark relationship of sclera to iris plays a critical role in face recognition from early in development. Specifically, we tested face discrimination in 7- and 8-month-old infants while independently manipulating the contrast polarity of the eye region and of the rest of the face. This gave four face contrast polarity conditions: fully positive condition, fully negative condition, positive face with negated eyes (“negative eyes”) condition, and negated face with positive eyes (“positive eyes”) condition. In a familiarization and novelty preference procedure, we found that 7- and 8-month-olds could discriminate between faces only when the contrast polarity of the eyes was preserved (positive) and that this did not depend on the contrast polarity of the rest of the face. This demonstrates the critical role of eye contrast polarity for face recognition in 7- and 8-month-olds and is consistent with previous findings for adults.

Infants’ recognition of facial expressions develops during postnatal life. Previous studies have showed that infants learned to discriminate the facial expression of basic emotions such as happy or angry expressions by approximately 7 months of age. Although infants’ recognition of intense expressions has been demonstrated, their recognition of subtle expressions is unclear. The present study examined whether 6- to 7-month-old infants recognize the subtle anger expression. We presented the subtle expressions either as static or as dynamic displays. In static presentations, infants recognized the subtle anger expression. This result suggests that the infants have high sensitivity to angry expressions which signal a dangerous situation. In dynamic presentations, infants did not recognize the subtle anger expression. Infants around this age rarely see the dynamic anger expression in their daily lives. Their limited experience with dynamic expressions of anger might make it hard to recognize a dynamic subtle expression. Infants could learn to utilize facial motions in the development of recognition of facial expressions.

Both horizontal and vertical binocular disparities produce depth perception in adults. In developmental studies, infants aged around 4 to 6 months were shown to perceive depth from horizontal disparity. However, infants’ sensitivity to vertical disparity has not been shown clearly. To examine the sensitivity in infants, this study measured preferential looking behavior of infants aged 20 to 27 weeks. Results showed a significant preference for the stimulus with vertical disparity, providing the first evidence of infants’ sensitivity to vertical disparity. The infants in the same age group did not show preference for stimulus with horizontal disparity when the stimulus were comparable to the stimulus with vertical disparity, while their sensitivity to horizontal disparity was confirmed with the stimuli used in a previous study. Our results would suggest that properties in processing horizontal and vertical disparities are different in infancy, and that the sensitivity to horizontal disparity are still premature in 27 weeks after birth. Optical Review Optical Review Look Inside Share Share this content on Facebook Share this content on Twitter Share this content on LinkedIn Other actions Export citations Register for Journal Updates About This Journal Reprints and Permissions

We investigated illusory motion perception in 6-to-8-month-old infants using a static figure which produces strong illusory motion. In experiment 1 we prepared a control figure, which was physically similar to the illusory motion figure but which did not produce illusory motion. We presented the illusory figure and the control figure side-by-side, and measured infants' looking time at the target illusory figure. Results showed that the infants' looking time at the illusory figure was significantly longer than that for the control. In experiment 2 we made another set of stimuli consisting of the same local pattern used in experiment 1, but which did not produce illusory motion. The results showed that no preferences were observed in experiment 2. These results suggest that 6-to-8-month-old infants perceive illusory motion in static figures.

To examine young infants' sensitivity to a pictorial depth cue, we compared monocular and binocular preferential looking to objects of which depth was specified by height-in-the-picture-plane. For adults, this cue generates the perception that a lower object is closer than a higher object. This study showed that 4- and 5-month-old infants fixated the lower, apparently closer, figure more often under the monocular than binocular presentation providing evidence of their sensitivity to the pictorial depth cue. Because the displays were identical in the two conditions except for binocular information for depth, the difference in looking-behavior indicated sensitivity to depth information, excluding a possibility that they responded to 2D characteristics. This study also confirmed the usefulness of the method, preferential looking with a monocular and binocular comparison, to examine sensitivity to a pictorial depth cue in young infants, who are too immature to reach reliably for the closer of two objects.

Newborn infants prefer face-like patterns over non-face-like patterns. This preference is explained by newborns' preference for a “top-heavy” configuration, that is, for geometric patterns that have more elements in the upper part than in the lower part of the configuration (Simion, Valenza, Macchi Cassia, Turati, & Umilta, 2002). However, for 3-month-old infants, face preference cannot be explained only by a preference for “top-heaviness” because they prefer veridical face images over top-heavy images. The present study used geometric patterns to investigate whether 2- to 3-month-old infants' preference for face patterns exceeds their preference for top-heavy configurations. In Experiment 1, we revealed that the infants preferred the face pattern to the top-heavy pattern only when the internal elements of the patterns were presented with face-like movements. This facilitative effect of internal movement was observed again in Experiment 2, in which the patterns were presented with non-face-like movements. These results suggest that 2- to 3-month-olds' preference for geometric face patterns is greater than their preference for top-heavy patterns only when aided by the movement of internal elements.

We examined the ability of young infants (3- and 4-month-olds) to detect faces in the two-tone images often referred to as Mooney faces. In Experiment 1, this performance was examined in conditions of high and low visibility of local features and with either the presence or absence of the outer head contour. We found that regardless of the presence of the outer head contour, infants preferred upright over inverted two-tone face images only when local features were highly visible (Experiment 1a). We showed that this upright preference disappeared when the contrast polarity of two-tone images was reversed (Experiment 1b), reflecting operation of face-specific mechanisms. In Experiment 2, we investigated whether motion affects infants’ perception of faces in Mooney faces. We found that when the faces appeared to be rigidly moving, infants did show an upright preference in conditions of low visibility of local features (Experiment 2a). Again the preference disappeared when the contrast polarity of the image was reversed (Experiment 2b). Together, these results suggest that young infants have the ability to integrate fragmented image features to perceive faces from two-tone face images, especially if they are moving. This suggests that an interaction between motion and form rather than a purely motion-based process (e.g., structure from motion) facilitates infants’ perception of faces in ambiguous two-tone images.

Arcimboldo images induce the perception of faces when shown upright despite the fact that only nonfacial objects such as vegetables and fruits are painted. In the current study, we examined whether infants recognize a face in the Arcimboldo images by using the preferential looking technique and near-infrared spectroscopy (NIRS). In the first experiment, we measured looking preference between upright and inverted Arcimboldo images among 5- and 6-month-olds and 7- and 8-month-olds. We hypothesized that if infants perceive the Arcimboldo images as faces, they would prefer the upright images to the inverted ones. We found that only 7- and 8-month-olds significantly preferred upright images, suggesting that they could perceive the Arcimboldo images as faces. In the second experiment, we measured hemodynamic responses using NIRS. Based on the behavioral data, we hypothesized that 7- and 8-month-olds would show different neural activity for upright and inverted Arcimboldo images, as do adults. Therefore, we measured hemodynamic responses in 7- and 8-month-olds while they were looking at upright and inverted Arcimboldo images. Their responses were then compared with the baseline activation during the presentation of individual vegetables. We found that the concentration of oxyhemoglobin increased in the left temporal area during the presentation of the upright images compared with the baseline during the presentation of vegetables. The results of the two experiments suggest that (a) the ability to recognize the upright Arcimboldo images as faces develops at around 7 or 8 months of age and (b) processing of the upright Arcimboldo images is related to the left temporal area of the brain.

A visual pattern's orientation influences how adults amodally complete that pattern. We examined whether this is also the case with infants using Markovich's pattern, consisting of a black polygon partially occluded by a gray disc, which is completed as either a vertically symmetrical hexagon or as a pentagon, depending on the pattern's orientation. Our experiment consisted of two prefamiliarization test trials, six familiarization trials, and two postfamiliarization test trials. In the familiarization trials, two identical Markovich patterns, upright or slanted, were presented to 7–8-month-old infants (N = 28) side by side on a CRT monitor. In the pre- and postfamiliarization test trials, a pentagon and a hexagon were presented side by side. Infants looked longer at the hexagon than at the pentagon in the postfamiliarization test trials. This suggests that infants completed the pattern as a pentagon regardless of the pattern's orientation. This lack of an orientation effect suggests that infants do not use the figure's symmetry as a guiding principle for amodal completion.

A preference for static face patterns is observed in newborns and disappears around 3 months after birth. A previous study has demonstrated that 5-month-old infants prefer schematic faces only when the internal features are moving, suggesting that face-specific movement enhances infants' preference. The present study investigates the facilitative effect of the movement of internal facial features on infants' preference. To examine infants' preference, we used animated face patterns consisting of a head-shaped contour and three disk blobs. The inner blobs expanded and contracted to represent the opening and closing of the eyes and mouth, and were constrained to open and close only in a biologically possible vertical direction resembling the facial muscle structure. We compared infants' preferential looking time for this vertically moving (VM) face pattern with their looking time for a horizontally moving (HM) face pattern in which blobs transformed at the same speed in a biologically impossible, horizontal direction. In Experiment 1, 7 to 8-month-olds preferred the VM to the HM, but 5 to 6-month-olds did not. However, the preference was diminished in both cases when the moving face patterns were presented without contour (Experiment 2). Our results suggest that internal facial features with vertical movements promote face preference in 7 to 8-month-olds. Copyright © 2011 John Wiley & Sons, Ltd.

We examined glossiness perception in infants using a preferential looking paradigm. In experiment 1, the images of two doll-shaped objects with matte and glossy surfaces were presented to infants aged 5 to 6 and 7 to 8 months. The results showed that the 7 to 8 month olds, but not the 5 to 6 month olds, looked significantly longer at the glossy object than at the matte object. In experiment 2, we additionally employed an object that was matte and covered with textures of white paint splashes, whose luminance histogram was almost identical to that of the glossy object. The results showed that the 7 to 8 month old infants could discriminate between the glossy object and the textured object even though both had similar luminance histograms. Qualitatively similar results were obtained for simple spheres that did not contain facial features. Therefore, the results of experiments 1 and 2 were not due to differences in the visibility of the dolls' facial features. These findings suggest that 7 to 8 month old infants perceive difference between glossy objects and matte objects on the basis of surface representations.

Recognition of other people's facial expressions of emotion plays an important role in social communication in infants as well as adults. Evidence from behavioral studies has demonstrated that the ability to recognize facial expressions develops by 6 to 7 months of age. Although the regions of the infant brain involved in processing facial expressions have not been investigated, neuroimaging studies in adults have revealed that several areas including the superior temporal sulcus (STS) participate in the processing of facial expressions. To examine whether the temporal area overlying the STS is responsible for the processing of facial expressions in infants, near-infrared spectroscopy (NIRS) was used to measure the neural activity in the temporal area overlying the STS as infants looked at happy and angry faces. NIRS provides a non-invasive means of estimating cerebral blood flow in the human brain and does not require severe constraints of head-movement. According to the International 10-20 system for EEG electrode placement, the measurement area was located in the bilateral temporal area centered at positions T5 and T6, which correspond to the STS. The time-course of the average change in total-Hb concentration revealed a clear difference in the pattern of hemodynamic responses to happy and angry faces. The hemodynamic response increased gradually when infants looked at happy faces and was activated continuously even after the disappearance of the face. In contrast, the hemodynamic responses for angry faces increased during the presentation of angry faces, then decreased rapidly after the face disappeared. Moreover, the left temporal area was significantly activated relative to the baseline when infants looked at happy faces, while the right temporal area was significantly activated for angry faces. These findings suggest hemispheric differences in temporal areas during the processing of positive and negative facial expressions in infants.

We investigated whether infants experience the hollow-face illusion using a screen-based presentation of a rotating hollow mask. In experiment 1 we examined preferential looking between rotating convex and concave faces. Adults looked more at the concave—illusory convex—face which appears to counter rotate. Infants of 7- to 8-month-old infants preferred the convex face, and 5- to 6-month-olds showed no preference. While older infants discriminate, their preference differed from that of adults possibly because they don't experience the illusion or counter rotation. In experiment 2 we tested preference in 7- to 8-month-olds for angled convex and concave static faces both before and after habituation to the stimuli shown in experiment 1. The infants showed a novelty preference for the static shape opposite to the habituation stimulus, together with a general preference for the static convex face. This shows that they discriminate between convex and concave faces and that habituation to either transfers across a change in view. Seven- to eight-month-olds have been shown to discriminate direction of rigid rotation on the basis of perspective changes. Our results suggest that this, perhaps together with a weaker bias to perceive faces as convex, allows these infants to see the screen-based hollow face as hollow even though adults perceive it as convex.

We investigated the effect of the regular sequence of different views and the three-quarter view effect on the learning of unfamiliar faces by infants. 3–8-month-old infants were familiarized with unfamiliar female faces in either the regular condition (presenting 11 different face views from the frontal view to the left-side profile view in regular order) or the random condition (presenting the same 11 different face views in random order). Following the familiarization, infants were tested with a pair of a familiarized and a novel female face either in a three-quarter (Experiment 1) or in a profile view (Experiment 2). Results showed that only 6–8-month-old infants could identify a familiarized face in the regular condition when they were tested in three-quarter views. In contrast, 6–8-month-old infants showed no significant novelty preference in profile views. The results suggest that the regular sequence of different face views promotes the learning of unfamiliar faces by infants over 6 months old. Moreover, our findings imply that the three-quarter view effect appears in infants.

We examined two hypotheses about infants' perception of orientation. The first is that infants develop an expectation that the human body is normally vertical. To examine this hypothesis, we compared the preferential looking to vertical and oblique versions of a silhouette of a human body, to an inverted body, and to a grating. Our second hypothesis is that presenting a figure inside a frame affects the perception of orientation. To examine the second hypothesis, we placed the figure inside a surrounding square that was oriented normally or at an oblique angle. Four- to seven-month-old infants (N = 78) participated. The results showed that 6–7-month-old infants preferred the oblique human body presented upright; no such preference was observed for the inverted body or the grating. For all types of displays, the surrounding square influenced preferences. Our results suggest that (a) 6–7-month-old infants have specific expectations about the orientation of the human body, and (b) surrounding displays with a square could influence the perception of the orientation of the human body, as well as that of a grating.

Radial optic flow is one of the crucial cues for the perception of motion-in-depth and contributes to our daily adaptive actions such as locomotion or postural control. Although many researchers have examined the development of radial motion perception and that of adaptive motor actions, no valid developmental model for visuo-motor coordination has been proposed. In the present study, we tried to propose a developmental framework for the interactive process between visual radial motion perception and the adaptive motor actions in infancy, with a brief review of the previous psychophysical, psychophysiological, and neurophysiological studies. The effect of the functional development of the posterior parietal cortex, which might be induced by the experiences of ego motion in particular developmental periods, on visuo-motor coordination was discussed.

This study examined the perception of the rotating Kanizsa square by using a fixed-trial familiarization method. If the Kanizsa square is rotated across the pacmen, adult observers perceive not only a rotating illusory square, but also an illusory expansion/contraction motion of this square. The phenomenon is called a "rotational dynamic illusion". In experiments 1 and 2, we investigated whether infants perceived the rotational dynamic illusion, finding that 3-8-month-old infants perceived the rotational dynamic illusion as a simple rotation of the Kanizsa square. In experiment 3, we investigated whether infants perceived the rotational dynamic illusion as a rotation of the Kanizsa square or as a deformation of shape, finding that 3-4-month-old infants did perceive the rotational dynamic illusion as a rotation of the Kanizsa square. Our results show that while 3-8-month-old infants perceive the rotating Kanizsa square, however, it is difficult for the infants to extract expansion/contraction motion from the rotational dynamic illusion.

The Ebbinghaus illusion is a geometric illusion based on a size-contrast between a central circle and surrounding circles. A central circle surrounded by small inducing circles is perceived as being larger than a central circle surrounded by large inducing circles. In the present study we investigated 5- to 8-month-old infants' perception of the Ebbinghaus illusion using a preferential-looking paradigm. We measured the preference between a central circle surrounded by small inducing circles (overestimated figure) and a central circle surrounded by large inducing circles (underestimated figure). Infants showed a significant preference for the overestimated figure when the central circle was flashing, but not when it was static. Furthermore, there was no preference between the two figures when the central circles were removed. These results suggest that infants' preference reflects their perception of the size illusion of the central circle. There is a possibility that 5- to 8-month-old infants perceive the Ebbinghaus illusion.

We explored infants' ability to recognize the canonical colors of daily objects, including two color-specific objects (human face and fruit) and a non-color-specific object (flower), by using a preferential looking technique. A total of 58 infants between 5 and 8 months of age were tested with a stimulus composed of two color pictures of an object placed side by side: a correctly colored picture (e.g., red strawberry) and an inappropriately colored picture (e.g., green-blue strawberry). The results showed that, overall, the 6- to 8-month-olds showed preference for the correctly colored pictures for color-specific objects, whereas they did not show preference for the correctly colored pictures for the non-color-specific object. The 5-month-olds showed no significant preference for the correctly colored pictures for all object conditions. These findings imply that the recognition of canonical color for objects emerges at 6 months of age.

Using near-infrared spectroscopy (NIRS), we recorded changes of oxy-Hb, deoxy-Hb, and total-Hb in 7- to 8-month-old infants' and adults' brains in response to canonical face and scrambled face stimuli. Using a newly developed probe for NIRS recording, which was light and soft enough to be tolerated by infants, we were able to acquire data from the very young even in the awake state. Total-Hb in response to a canonical face stimulus was greater than for scrambled face stimuli only in the right hemisphere in infants. This indicates the presence of right hemisphere dominance of brain activity in response to face images in 7- to 8-month-old infants. In adults, oxy-Hb and total-Hb were significantly increased from baseline only for the canonical face in the right hemisphere. There were greater numbers of channels showing significantly increased activity for the canonical face in the right than in the left hemisphere. These data indicate that the right hemisphere is more dominant for canonical face perception in both infants and adults. However, overall, the increase of total-Hb and oxy-Hb in adults was modest compared to infants. Although the reason for the difference between infants and adults is unclear, in addition to developmental changes influencing face perception, some methodological problems may be present. Thus, because we recorded NIRS signals in infants and adults using the same method, anatomical and physiological problems might affect the results to some degree. Although comparing the results between infants and adults is not simple, the present study is the first to indicate how 7- to 8-month-old infants perceive scrambled face stimuli and to compare such results with those of adults in order to understand developmental changes in face perception.