There’s a look of love, a mask of fear, an expression of disgust. We speak the language of emotion primarily through our face and eyes, and it wouldn't be a stretch to say that most of us believe the expression in our own and others’ eyes is all about communicating emotions. But according to a new study conducted by Cornell University neuroscientists, our facial expressions developed from the need to filter where and what we see and may have very little to do with social communication.

Adam Anderson, professor of human development in Cornell’s College of Human Ecology, would even go so far as to suggest that our facial expressions are universal, adaptive reactions to environmental stimuli. “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,” said Anderson, whose work with co-authors is published in the journal, Psychological Science.

The Experiments

Two-thirds of the eye’s optical power come from the cornea, the clear dome-shaped structure that covers the front part of the eye. When we widen or narrow our eyes, then, how much light and the angle at which it hits our cornea changes — and with this our visual abilities change, too. The team of Cornell researchers hypothesized since eyes widening and narrowing mimic the way the pupil dilates and constricts, facial expressions must also change the function of the eyes. Does widening the eyes, as we do when we feel fear, help us to locate a stimulus or to identify and discriminate a stimulus? What purpose does narrowing the eyes when we feel disgust serve in terms of our visual capacity?

To explore whether our different facial expressions created “an optical trade-off,” enhancing either the sensitivity or the acuity of our eyes, the researchers set up an experiment where they began by measuring the left-eye sensitivity of 11 participants from the University of Toronto with normal or corrected-to-normal vision (contact lenses were allowed, but glasses were not because of the way they obstruct the visual-field). Next, participants were tested in three sessions on three separates days while the participants made three different expressions — fear, neutral, and disgust. “These emotions trigger facial expressions that are very far apart structurally, one with eyes wide open and the other with eyes pinched,” Anderson stated in a press release. While participants made each expression, the researchers recorded optical responses to detect light stimuli of varying luminance at 54 locations, arranged in a 6-degree grid on a visual-field hemisphere.

What did the researchers discover? Widening their eyes in fear enhanced the participants’ abilities to pick up on information at low light levels. Narrowing their eyes in disgust, on the other hand, impaired participants' sensitivity but enhanced their ability to see things at a finer scale. “The reason for that is to allow the eye to harness the properties of light that are most useful in these situations,” Anderson said. Ultimately, then, fearful expressions resulted in maximum sensitivity — more light and a broader visual field. Looks of disgust resulted in maximum acuity — less light and better focus.

“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. “We tend to think of perception as something that happens after an image is received by the brain, but in fact emotions influence vision at the very earliest moments of visual encoding.”

Having completed this experiment, Anderson is now studying how different eye movements account for the ways facial expressions have developed across cultures to support nonverbal communication. “We are seeking to understand how these expressions have come to communicate emotions to others,” he said.

Source: Lee DH, Mirza R, Flanagan JG, Anderson AK. Optical Origins of Opposing Facial Expression Actions. Psychological Science. 2014.