Eye wrinkles make you appear more sincere whether your expression is associated with sadness, happiness, or pain. According to a collaborative study by researchers from the University of Miami and Western University in Canada, our brains are pre-wired to perceive wrinkles in such a manner.

The study “Generalizing Duchenne to Sad Expressions with Binocular Rivalry and Perception Ratings” was published in the American Psychological Association journal Emotion.

You have probably heard of “smiling with your eyes,” or “his/her smile doesn't reach their eyes,” and other such sayings. In the 19th century, French neurologist Guillaume Duchenne identified the smile which raises the cheeks and forms wrinkles around and out the corners of the eyes as the Duchenne smile

“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,” said Dr. Daniel Messinger, a psychology professor at the University of Miami. “This research suggests one key to this language is constriction of the eyes, which appears to intensify both positive and negative expressions.”

For the study, the researchers used a method called visual rivalry which showed participants pictures of computer-generated avatars having Duchenne and non-Duchenne smiles. The method prioritized the unconscious and also what our brains involuntarily see, according to lead investigator Dr. Julio Martinez-Trujillo from Western University.

After different images were shown in each eye, the participants were asked to rate the expressions based on intensity and sincerity. The results showed they systematically ranked the Duchenne smiles as well as sad expressions as more sincere and intense than the non-Duchenne expressions.

“The expressions involving the Duchenne marker were always dominant,” Martinez-Trujillo said. “So if the emotion is more intense, your brain actually prefers to bring it into perceptual awareness for a longer time.”

The authors wrote how these results may be evidence in favor of Darwin who hypothesized specific facial actions have a general function — which is to convey intensification and sincerity — across expressions. 

Messinger explained how the hypothesis was investigated for more than a decade, citing a previous study of his, which supported how eye constriction intensified positive and negative expressions in infants.

“This is the first study addressing this issue in adults since Darwin's provocative observations,” he said.

The research may add more depth to help us understand how human beings read each other and highlight the extent of a potential universal language for reading emotions. Some facial expressions and gestures (such as direct eye contact or open-mouth laughing) are perceived differently across various countries and cultures.

In the future, Martinez-Trujillo hopes to conduct the same test on participants diagnosed 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,” he explained.