Study: Humans Can Make More Than 20 Distinct Facial Expressions

You will raise your eyebrows and curl up the corners of your mouth when you realize what this new study has discovered about emotion processing.
A sample of the facial expressions subjects were asked to portray (Aleix M. Martinez/PNAS)

For years, scientists studying facial expressions have focused their research on six primary emotions: happiness, surprise, anger, sadness, fear, and disgust.

As a result generations of facial-expression research papers have included panels that look something like this:

Journal of Experimental Psychology

(That one is from a paper about cultural differences in the perception of facial expressions.)

Aleix M. Martinez/PNAS

Pretty straightforward, right? But when is the last time you saw someone looking just surprised, rather than, say surprised at an impromptu birthday getaway (happy surprise) or surprised at a toddler’s art project, crafted with the media “peanut butter” and “wall” (angry surprise).

Researchers from the Ohio State University suspected that there’s more to the human condition than these six simplest states of being. For example, as they wrote in a study published today in the Proceedings of the National Academy of Sciences, “Appall is the act of feeling disgust and anger with the emphasis being on disgust; i.e., when appalled we feel more disgusted than angry. Hate also involves the feeling of disgust and anger but, this time, the emphasis is on anger.”

To prove that humans could make, and perceive, a wider range of feelings with their faces, the study authors asked 230 subjects to make a face depicting each of the following 20 sentiments: happy, sad, fearful, angry, surprised, disgusted, happily surprised, happily disgusted, sadly fearful, sadly angry, sadly surprised, sadly disgusted, fearfully angry, fearfully surprised, fearfully disgusted, angrily surprised, angrily disgusted, disgustedly surprised, hatred, and awed.

Here's how they look when laid end-to-end:

Aleix M. Martinez/PNAS

Careful, dude, it might stick that way.

The researchers then analyzed the facial muscles the subjects used to generate each expression. They found that while the “Basic Six” emotions correlated with very distinct “action units,” or facial muscle movements, the combined emotions incorporated muscle movements of both of their parent emotions. So, for example, a happy person might be smiling, and a disgusted person might scrunch her nose, but a happily disgusted person (“This whole cheesecake all for me!?”) would do both.

Here’s the happily disgusted example, as well as fearful and surprised, which combine into “awed”:

Aleix M. Martinez/PNAS

The authors determined that the more complex facial expressions were each formed using a unique combination of muscle movements. And though it confused expressions like “angrily surprised” and “sadly surprised,” a computer algorithm was otherwise able to correctly classify the compound expressions about 77 percent of the time. This suggested to the researchers that there was a great degree of similarity between the subjects’ portrayals of complex feelings like “hatred” or “appalled.”

This study might open interesting avenues of research into disorders that impede the processing of emotions, like schizophrenia and autism.

The researchers write that this might also help people who work in human-computer interaction teach computers a broader range of human emotion. You know, so that when the robot revolution occurs, our cyborg overlords will be able to tell whether you’re angrily surprised or sadly disgusted that you’re being forced into a lifetime of servitude in their steel-plated underground garrisons.

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Olga Khazan is a staff writer at The Atlantic, where she covers health.

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