Considering that changes in pupil size are closely tied to changes in physiological arousal controlled by the autonomic nervous system, it is possible that the coordination of arousal between social partners facilitates pupil mimicry or alternatively that pupil mimicry facilitates the unconscious coordination of arousal between social partners 6, 7, 8, 9, 10. Similarly, infants 6 to 9 months of age show greater pupil dilation when viewing larger compared to smaller schematic eyes 7, 8. Specifically, infants as young as 4 months of age display greater pupil dilation when viewing photographs of dilated eyes, suggesting pupil dilation mimicry 7. Recent work shows that early in ontogeny humans already differentially respond to changes in others’ pupil size (diameter). Though this preference has been shown to emerge in early adulthood, much less is known about how infants perceive and respond to pupillary cues. By adulthood, a preference develops for individuals with larger pupils and pupil dilation is recognized as a signal for positive affect 4, 6. During face-to-face social interactions, information regarding a person’s attentional, emotional, and mental state can be gleaned from the eye region and from the pupillary state 3, 4, 5. The ability to detect and respond to information from the eyes is an early developing capacity that is considered a foundational feature of human social cognition in infancy 1, 2. This critically informs our understanding of the early origins of responding to pupillary signals in others and further highlights the impact of race on the processing of social signals. These findings suggest that, early in development, the fundamental process of responding to pupillary changes is impacted by race and interracial interactions may afford greater cognitive control or effort. Moreover, when processing other-race pupillary changes, infants recruited the dorsolateral prefrontal cortex, a brain region linked to cognitive control functions.

Specifically, infants showed enhanced responses in the right superior temporal cortex when observing own-race pupil dilation. Our results show that only when responding to own-race eyes, infants’ brains distinguished between changes in pupillary size.

We measured 9-month-old infants’ brain responses to dilating and constricting pupils in the context of viewing own-race and other-race eyes using functional near-infrared spectroscopy (fNIRS). Here, we examined whether and how race impacts the neural processing of others’ pupillary changes in early ontogeny. Among adults, perception of pupillary changes is affected by race. Recently, infants have been found to mimic observed pupillary changes in others, instantiating a foundational mechanism for eye-based social communication. Observed changes in pupillary size provide a range of socially-relevant information including cues regarding a person’s emotional and arousal states. Sensitive responding to eye cues plays a key role during human social interactions.

One pupil larger than other