University of Miami Psychology Professor Daniel Messinger collaborated with researchers at Western University in Canada to show that our brains are pre-wired to perceive wrinkles around the eyes as conveying more intense and sincere emotions. This eye wrinkle, called the Duchenne marker, occurs across multiple facial expressions, including smiles, expressions associated with pain, and --as these researchers found--expressions of sadness.
"Since Darwin, scientists have wondered if there is a language of facial expression, a key set of what we call facial actions which have simple, basic meanings. This research suggests one key to this language is constriction of the eyes, which appears to intensify both positive and negative expressions," said Messinger.
Using a method called visual rivalry, the researchers showed study participants computer-generated avatars, one with and one without the Duchenne marker, to study which expressions our brains perceive as more important. When different images are shown in each eye, the brain alternates between these two images and will bring the image that is perceived as more relevant into perceptual awareness more often.
"When you have social interactions, you need to perceive whether a person is sincere or not," said the principal investigator on the study, Julio Martinez-Trujillo, a professor at Western's Schulich School of Medicine & Dentistry. "My interest now is: what will be the results if we do this same test with people with autism spectrum disorder? They often have trouble reading out emotions from other people, so we wonder if that might have to do with their ability to read this marker for sincerity."
The investigators asked participants to rate the expressions on a scale for intensity and sincerity, and found that people systematically ranked the Duchenne smiles and Duchenne sad expressions as more sincere and intense than the non-Duchenne expressions.
The authors point out that the results are a step toward understanding the more general questions of why facial expressions contain the specific facial actions they do, and how that contributes to our understanding of emotion.
"We have been investigating this hypothesis for more than a decade and finding strong support that eye constriction intensifies positive and negative expression in infants, with others finding support for the intensification hypothesis in children," adds Messinger. "This is the first study addressing this issue in adults since Darwin's provocative observations."
The study, "Generalizing Duchenne to Sad Expressions with Binocular Rivalry and Perception Ratings," was published in the journal Emotion.