Humans are the only primates with large, highly visible sclera - the white part of the eye. The eye plays a significant role in the expressiveness of a face, and how much sclera is shown can indicate the emotions or behavioral attitudes of a person. Wide-open eyes, exposing a lot of white, indicate fear or surprise. A thinner slit of exposed eye, such as when smiling, expresses happiness or joy. Averted eyes, as well as direct eye contact, can mean several things. So the eye white, or how much of it is shown and at what angle, plays arole in the social and cooperative interactions among humans.
Adult humans are well-attuned to social cues involving the eye and use them, along with a great range of other facial and body features, to respond appropriately during social interactions. This sensitivity to eye cues is hard-wired into the brain of adults as they respond to social eye cues even without consciously seeing them.
But it is unclear whether the ability to unconsciously distinguish between different social cues indicated by the eyes exists early in development and can therefore be considered a key feature of the human social makeup. A new University of Virginia and Max Planck Institute study, published in the journal Proceedings of the National Academy of Sciences, finds that the ability to respond to eye cues apparently develops during infancy - at seven or so months.
"Our study provides developmental evidence for the notion that humans possess specific brain processes that allow them to automatically respond to eye cues," said Tobias Grossmann, one of the authors from the University of Virginia.
