Researchers reveal why the eyes offer a window into the soul

A new study gives insight on how a universal reaction to environmental stimuli evolved to communicate our deepest emotions. In other words, how and why the eyes offer a window into the soul.

Charles Darwin’s 19th-century theories on the evolution of emotion hypothesized that our expressions originated for sensory function rather than social communication. Two studies support that theory, and new research by Adam Anderson, professor of human development at Cornell University’s College of Human Ecology, shows that we interpret a person’s emotions by analyzing the expression in their eyes.

In 2013, Anderson demonstrated that human facial expressions, such as raising one’s eyebrows, arose from universal, adaptive reactions to one’s environment and did not originally signal social communication. Building on that research, Anderson and his co-author, Daniel H. Lee, professor of psychology and neuroscience at the University of Colorado, Boulder, created models of six expressions – sadness, disgust, anger, joy, fear and surprise – using photos of faces in widely used databases.

According to a press release, study participants were shown a pair of eyes demonstrating one of the six expressions and one of 50 words describing a specific mental state, such as discriminating, curious, bored, etc. Participants then rated the extent to which the word described the eye expression. Each participant completed 600 trials. Participants consistently matched the eye expressions with the corresponding basic emotion, accurately discerning all six basic emotions from the eyes alone.

Anderson then analyzed how these perceptions of mental states related to specific eye features. Those features included the openness of the eye, the distance from the eyebrow to the eye, the slope and curve of the eyebrow, and wrinkles around the nose, the temple and below the eye.

The study found that the openness of the eye was most closely related to our ability to read others’ mental states based on their eye expressions. Narrow-eyed expressions reflected mental states related to enhanced visual discrimination, such as suspicion and disapproval, while open-eyed expressions related to visual sensitivity, such as curiosity. Other features around the eye also communicated whether a mental state is positive or negative.

Further, he ran more studies comparing how well study participants could read emotions from the eye region to how well they could read emotions in other areas of the face, such as the nose or mouth. Those studies found the eyes offered more robust indications of emotions.

This study, said Anderson, was the next step in Darwin’s theory, asking how expressions for sensory function ended up being used for communication function of complex mental states.

“The eyes evolved over 500 million years ago for the purposes of sight but now are essential for interpersonal insight,” Anderson said.

The study “Reading What the Mind Thinks From How the Eye Sees” was published recently in Psychological Science.