The fact that we infer other people's emotions based on their facial expressions isn't entirely new.
With that in mind, however, a pair of researchers from New York and Colorado have set out to investigate how exactly these expressions communicate so many complex mental and emotional states.
How We Read Emotions
Daniel H. Lee and Adam K. Anderson used photos of faces taken from databases and created average models of six expressions, namely disgust, sadness, fear, anger, surprise, and joy.
The pair asked study participants to look at these photos along with a word that represented a certain mental state. The participants, who completed 600 trials, rated the extent to which the word described the expression of the eyes on the photos.
Lee and Anderson then analyzed how these observations are linked to specific eye features, which included the distance from the eyebrow to the eye, the openness of the eye, the curve and slope of the eyebrows, and the wrinkles around the temple, nose, and below the eye.
The results suggest that the eyes really do offer a strong signal of emotional state. Participants matched eye expressions with corresponding emotions, and they provided four distinct clusters for the link between eye features and emotions.
"Human expressions are highly complex," said Lee.
For instance, eye-widening features are associated with awe, information sensitivity, cowardice, interest, and anticipation. On the other hand, eye-narrowing features are related to suspicion, aggressiveness, contempt, and hate.
Two extra clusters included features associated with sadness, which aligned with uneasiness, as well as joy, which aligned with admiration.
How Our Eyes See
Lee and Anderson believe how we see directly relates to how others see us. Lee gave an example: if you are watching a show like "Curb Your Enthusiasm," you will notice that Larry David narrows his eyes for scrutiny. That emotion is communicated to you, the viewer.
Charles Darwin's theory on how expressions evolved to have a sensory function for the sender became the basis of this study, said Lee. It means that sensory function also evolved for the receiver.
Furthermore, the researchers said widening our eyes bolsters visual sensitivity and allows more light in, which helps us see whether there are threats lurking nearby.
When we squint our eyes, it can boost our visual acuity and help us distinguish fine details. These expressions may have been designated for social purposes and now operate as signals for mental states.
Details of the study are published in the journal Psychological Science.