The ability to respond to eye cues develops during infancy - at around seven months, a new research has found.
The eye plays a significant role in the expressiveness of a face, and how much sclera - the white part of the eye - is shown can indicate the emotions or behavioural 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.
The study found 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, a University of Virginia developmental psychologist and one of the study's authors.
Grossmann and colleague Sarah Jessen from the Max Planck Institute used electroencephalography or EEG to measure the brain activity of 7-month-old infants while showing images of eyes wide open, narrowly opened, and with direct or averted gazes.
They found that the infants' brains responded differently depending on the expression suggested by the eyes they viewed, which were shown absent of other facial features.
They viewed the eye images for only 50 milliseconds - which is much less time than needed for an infant of this age to consciously perceive this kind of visual information.
"Their brains clearly responded to social cues conveyed through the eyes, indicating that even without conscious awareness, human infants are able to detect subtle social cues," Grossmann said.
The infants' brain responses displayed a different pattern to sclera depicting fearful expressions (wide-eyed) to non-fearful sclera. They also showed brain responses that differed when viewing direct gaze eyes compared to averted gaze.
"This demonstrates that, like adults, infants are sensitive to eye expressions of fear and direction of focus, and that these responses operate without conscious awareness," Grossmann said.
"The existence of such brain mechanisms in infants likely provides a vital foundation for the development of social interactive skills in humans," said Grossmann.
The infants in the study wore an EEG cap, like a small hat, which included sensors that could detect brain signals.
The study was published in the journal PNAS.
