The other-race effect of pupil contagion in infancy.

Pupil contagion refers to the observer's pupil-diameter changes in response to changes in the pupil diameter of others. Recent studies on the other-race effect on pupil contagion have mainly focused on using eye region images as stimuli, revealing the effect in adults but not in infants. To address this research gap, the current study used whole-face images as stimuli to assess the pupil-diameter response of 5-6-month-old and 7-8-month-old infants to changes in the pupil-diameter of both upright and inverted unfamiliar-race faces. The study initially hypothesized that there would be no pupil contagion in either upright or inverted unfamiliar-race faces, based on our previous finding of pupil contagion occurring only in familiar-race faces among 5-6-month-old infants. Notably, the current results indicated that 5-6-month-old infants exhibited pupil contagion in both upright and inverted unfamiliar-race faces, while 7-8-month-old infants showed this effect only in upright unfamiliar-race faces. These results demonstrate that the face inversion effect of pupil contagion does not occur in 5-6-month-old infants, thereby suggesting the presence of the other-race effect in pupil contagion among this age group. Overall, this study provides the first evidence of the other-race effect on infants' pupil contagion using face stimuli.

Attentional blink in infants under 7 months.

Attentional blink manifests in infants at 7 months of age, indicating that the working memory capacity of 7-month-olds is comparable to that of adults. However, attentional blink in infants under 7 months is not well understood. In this study, we conducted two experiments to investigate attentional blink in 5- and 6-month-old infants. The results of Experiment 1 demonstrated that attentional blinks were not observed with either a short lag (200 ms) or a long lag (800 ms). This suggests that 5- and 6-month-olds are unable to consolidate both targets regardless of the temporal distance between the two. We then split the infants into two groups by their age and conducted Experiment 2 with infants aged younger and older than 180 days to compare their consolidating ability to observe whether they could recognize a single item at 100-ms speed by presenting the same visual stream that was used in Experiment 1 except that one target was eliminated. The results showed that infants over 180 days of age could identify a single target in the visual stream at 100-ms presentation speed, whereas infants under 180 days could not. The findings of the current study indicate that the limitation of working memory capacity in infants under 7 months of age is a possible reason for the lack of attentional blink.

Emotional response in babies' pupil contagion.

In this study, it was investigated whether an emotional response would occur in pupil contagion by using skin conductance response (SCR) in 5- and 6-month-old infants. In the experiment, emotional responses to pupil diameter change (dilating/constricting) between the face and eyes regions were compared by using pupil diameter response and SCR. The results showed that pupil diameter responses to pupil diameter changes did not differ between face and eyes regions. The emotional response indicated by the SCR significantly increased when participants looked at dilating pupils of face stimuli compared with when participants looked at constricted pupils of face stimuli. In addition, we found a significant correlation between SCR and pupil dilation in the face. This means that pupil diameter expansion significantly increases emotional response in pupil dilation of the face region.

Metacontrast masking is ineffective in the first 6 months of life.

Metacontrast masking is one of the most widely studied types of visual masking, in which a visual stimulus is rendered invisible by a subsequent mask that does not spatially overlap with the target. Metacontrast has been used for many decades as a tool to study visual processing and conscious perception in adults. However, there are so far no infant studies on metacontrast and it remains unknown even whether it occurs in infants. The present study examined metacontrast masking in 3- to 8-month-old infants (N = 168) using a habituation paradigm. We found that metacontrast is ineffective for infants under 7 months and that younger infants can perceive a masked stimulus that older infants cannot. Our results suggest that metacontrast is distinct from other simple types of masking that occur in early infancy, and would be consistent with the idea that metacontrast results from the disruption of recurrent processing.

Infants' visual perception without feature-binding.

We reveal a unique visual perception before feature-integration of colour and motion in infants. Visual perception is established by the integration of multiple features, such as colour and motion direction. The mechanism of feature integration benefits from the ongoing interplay between feedforward and feedback loops, yet our comprehension of this causal connection remains incomplete. Researchers have explored the role of recurrent processing in feature integration by studying a visual illusion called 'misbinding', wherein visual characteristics are erroneously merged, resulting in a perception distinct from the originally presented stimuli. Anatomical investigations have revealed that the neural pathways responsible for recurrent connections are underdeveloped in early infants. Therefore, there is a possibility that younger infants could potentially perceive the physically presented visual information that adults miss due to misbinding. Here, we demonstrate that infants less than half a year old showed no misbinding; thus, they perceived the physically presented visual information, while infants more than half a year old perceived incorrectly integrated visual information, showing misbinding. Our findings indicate that recurrent processing barely functions in infants younger than six months of age and that visual information that should have been originally integrated is perceived as it is without being integrated.

Cortical signatures of visual body representation develop in human infancy.

Human infants cannot report their experiences, limiting what we can learn about their bodily awareness. However, visual cortical responses to the body, linked to visual awareness and selective attention in adults, can be easily measured in infants and provide a promising marker of bodily awareness in early life. We presented 4- and 8-month-old infants with a flickering (7.5 Hz) video of a hand being stroked and recorded steady-state visual evoked potentials (SSVEPs). In half of the trials, the infants also received tactile stroking synchronously with visual stroking. The 8-month-old, but not the 4-month-old infants, showed a significant enhancement of SSVEP responses when they received tactile stimulation concurrent with the visually observed stroking. Follow-up experiments showed that this enhancement did not occur when the visual hand was presented in an incompatible posture with the infant's own body or when the visual stimulus was a body-irrelevant video. Our findings provide a novel insight into the development of bodily self-awareness in the first year of life.

The role of scenic context on upright face preference in infancy.

Scenic information plays an important role in face processing, whereas it has received limited attention in the field of developmental research. In the current study, we investigated whether infants, like adults, utilize scenic information for face processing by the preferential-looking method. In Experiment 1, we examined 4-5 and 6-7-month-olds' visual preferences for upright faces compared to inverted faces in two surrounding scene conditions: intact (in which a face occurs in an intact scene) and scrambled (in which a face occurs in a jumbled scene). We found that 6- to 7-month-olds preferred the upright face in the intact scene, but not in the scrambled scene. Meanwhile, 4- to 5-month-olds showed significant upright face preference in both scenes. The results of Experiment 2 ruled out the possibility that the lack of preference for upright faces in the scrambled scene in 6- to 7-month-olds resulted from more distraction by the scrambledness of the image than occurs with 4- to 5-month-olds, by showing no developmental changes in preference either for the scrambled images or the intact images when faces did not appear. Our results suggest that infants aged 6 months or more utilize scenic information for face processing.

Recognition of humans from biological motion in infants.

Infant studies have suggested that the detection of biological motion (BM) might be an innate capacity, based on newborns' spontaneous preference for BM. However, it is unclear if, like adults, infants recognize humans from BM and are able to build the representation of bodies and faces. To address this issue, we tested whether exposure to BM influences subsequent face recognition in 3- to 8-month-old infants. After familiarization with a point-light walker (PLW) of either a female or a male, the infant's preference for female and male faces was measured. If infants can build the representation of not only the body but also the face from PLWs, the familiarization effect of gender induced by the PLW might be generalized to faces. We found that infants at 7 to 8 months looked for longer at the face whose gender was opposite to that of the PLW, whereas 3- to 4- and 5- to 6-month-old infants did not. These results suggest that infants can access the representation of humans from BM and extract gender, which is shared across bodies and faces, from at least 7 to 8 months of age.

Development of upper visual field bias for faces in infants.

The spatial location of the face and body seen in daily life influences human perception and recognition. This contextual effect of spatial locations suggests that daily experience affects how humans visually process the face and body. However, it remains unclear whether this effect is caused by experience, or innate neural pathways. To address this issue, we examined the development of visual field asymmetry for face processing, in which faces in the upper visual field were processed preferentially compared to the lower visual field. We found that a developmental change occurred between 6 and 7 months. Older infants aged 7-8 months showed bias toward faces in the upper visual field, similar to adults, but younger infants of 5-6 months showed no such visual field bias. Furthermore, older infants preferentially memorized faces in the upper visual field, rather than in the lower visual field. These results suggest that visual field asymmetry is acquired through development, and might be caused by the learning of spatial location in daily experience.

Infants' anticipatory eye movements: feature-based attention guides infants' visual attention.

When looking for an object, we identify it by selectively focusing our attention to a specific feature, known as feature-based attention. This basic attentional system has been reported in young children; however, little is known of whether infants could use feature-based attention. We have introduced a newly developed anticipation-looking task, where infants learned to direct their attention endogenously to a specific feature based on the learned feature (color or orientation), in 60 preverbal infants aged 7-8 months. We found that preverbal infants aged 7-8 months can direct their attention endogenously to the specific target feature among irrelevant features, thus showing the feature-based attentional selection. Experiment 2 bolstered this finding by demonstrating that infants directed their attention depending on the familiarized feature that belongs to a never-experienced object. These results that infants can form anticipation by color and orientation reflect they could drive their attention through feature-based selection.

Infants' Hemodynamic Modulation in the Temporal Region.

This study examined whether 8-month-old infants' hemodynamic responses in the temporal region were modulated by repeated presentation of "Peekaboo" by using functional near-infrared spectroscopy (fNIRS). Previous studies have shown that infants' temporal region responds to faces (e.g., Otsuka et al., 2007). A recent electroencephalography study showed that the neural activity of infants was modulated by repeated presentation of "Peekaboo." Some fNIRS studies also revealed that the movie of "Peekaboo" activated the hemodynamic response of the temporal region in infancy. However, no studies have shown the hemodynamic modulation of the temporal region according to the repeated presentation of "Peekaboo" in infants. In order to examine whether the hemodynamic responses of the temporal region were modulated by repeated presentation of "Peekaboo," we compared the activity of the temporal region between the early and late trials. We set long and short delays before face-presentation. The results showed that the concentration of oxy-hemoglobin in the right occipitotemporal region (Ch 21) in both conditions increased after the presentation of "Peekaboo" relative to the baseline. Moreover, in the long delay condition, the hemodynamic modulation of the right occipitotemporal region was induced according to the repeated presentation of "Peekaboo" in infants.

Infants' brain activity to cartoon face using functional near-infrared spectroscopy.

In this study, to investigate whether infants showed face-specific brain activity to a cartoon human face, we conducted a functional near-infrared spectroscopy (fNIRS) experiment and a behavioral experiment. In the fNIRS experiment, we measured the hemodynamic responses of 5- and 6-month-old infants to cartoon female and cartoon character faces using fNIRS. The results showed that the concentration of oxy-Hb increased for cartoon female faces but not for cartoon character faces. This indicates that face-specific brain activity occurred for cartoon female faces but not cartoon character faces, despite the fact that both are faces. In the behavioral experiment, we examined whether the 5- and 6-month-old infants preferred cartoon female faces to cartoon character faces in the upright and inverted conditions. The results showed a preference for cartoon female faces in the upright but not in the inverted condition. This indicates that 5- and 6-month-old infants can perceive cartoon female faces, but not cartoon character faces, as faces. The results of the two experiments indicated that face-specific brain activity occurred for cartoon female faces. This indicates that infants can perceive cartoon female faces as faces.

Cortical processing of dynamic bodies in the superior occipito-temporal regions of the infants' brain: Difference from dynamic faces and inversion effect.

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.

The other-race effect on the McGurk effect in infancy.

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.

Perception of invisible masked objects in early infancy.

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.

Attentional blink in preverbal infants.

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.

Face-Specific Pupil Contagion in Infants.

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.

The Development of Binocular Suppression in Infants.

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.

Development of the multisensory perception of water in infancy.

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.