Eyes may be the basis of all human facial expressions, according to new research.
Fear, anger and surprise produce facial expressions that maximize the way our eyes process light. This could have provided an evolutionary advantage when presented with predators and other dangers.
Adam Anderson of Cornell University led the study of facial expressions.
When anger grows in humans, our eyes squint, blocking some light from entering our vision. This allows us to focus on the potential foe. Fright causes the exact opposite effect, widening our eyes, bringing in more light, and expanding our field of vision. The additional light makes it easier to see objects in shadows, and a greater peripheral vision allows people to see possible threats to both sides.
Among animals, many prey animals, like deer, have eyes on each side of their heads, providing them a wide-field of view to search for predators. Meat-eaters, such as cats, tend to have eyes in front of the head, providing stereoscopic vision, perfect for hunting.
Feelings of disgust provide the best visual acuity and focus, using the least amount of light. Light intake was greatest when subjects were surprised. This could help shape the way humans see the world around us.
"These opposing functions of eye widening and narrowing, which mirror that of pupil dilation and constriction, might be the primitive origins for the expressive capacity of the face. And these actions are not likely restricted to disgust and fear, as we know that these movements play a large part in how perhaps all expressions differ, including surprise, anger and even happiness," Anderson said.
In cultures around the world, people share similar facial patterns to mark emotions. Sociologists often attribute this to social cues. This new research harkens back to the ideas of naturalist Charles Darwin, who first suggested the idea.
Anderson and his team built a model of a human eye, and changed the aperture of lens, simulating changes to the eye created by different facial expressions. This model was then subjected to standard vision tests for acuity and sensitivity.
Researchers believe this common feature to our species may be partly explained by the connection to vision. Looking for evidence of a connection is the next goal of Anderson and his team at Cornell.
"We are seeking to understand how these expressions have come to communicate emotions to others. We know that the eyes can be a powerful basis for reading what people are thinking and feeling, and we might have a partial answer to why that is," Anderson said.
Investigation of the connection between emotions and visual performance was detailed in the journal Psychological Science.
