Facial colors and emotions

It turns out that you don’t wear your heart on your sleeve. You wear it on your face.

Without moving a muscle, people convey a great deal about their feelings through their faces, and we all have a keen understanding of how others are feeling just by looking at them.

That’s according to a groundbreaking study into human expressions of emotion, conducted by researchers at The Ohio State University’s Center for Cognitive and Brain Sciences and funded by the National Institutes of Health.

They found people are able to correctly identify others’ feelings up to 75 percent of the time — based solely on subtle shifts in blood flow color around the nose, eyebrows, cheeks or chin. The study, published in the Proceedings of the National Academy of Sciences, demonstrated a never-before-documented connection between the central nervous system and emotional expression in the face.

“We identified patterns of facial coloring that are unique to every emotion we studied,” said Aleix Martinez, cognitive scientist and professor of electrical and computer engineering at Ohio State. He co-led the study with C. Fabian Benitez-Quiroz, a postdoctoral researcher, and Ramprakash Srinivasan, a doctoral student.

“We believe these color patterns are due to subtle changes in blood flow or blood composition triggered by the central nervous system. Not only do we perceive these changes in facial color, but we use them to correctly identify how other people are feeling," Martinez said.

The researchers are patenting the computer algorithms, and hope they will enable future forms of artificial intelligence to recognize and emulate human emotions.

This is the latest in a series of studies in which Martinez and his colleagues have identified unique forms of human facial expression.

In prior work, they identified several, previously unknown facial expressions produced though unique patterns of muscle movements, including the “not face,” or the frown understood universally as “no way,” “nope,” “uh-uh.”

What’s unusual about their latest work is that it involves color changes that communicate emotion without any movement of facial muscles.

Seeing red?

Touches of red, green, blue and yellow characterize every emotion — just in slightly different amounts or locations around the face, Martinez explained.

Disgust, for instance, creates a blue-yellow cast around the lips, but with a red-green cast around the nose and forehead.

It’s all the more impressive, then, that our brains are able to decipher the meaning of these color arrangements in an instant.

We see a smiling person with red cheeks and temples (with a little blue around the chin) and we automatically read their emotion as “happy.” But the same face with a slightly redder forehead and slightly less blue chin registers as “surprised.”

Humans just may be alone among primates for our ability to change facial color due to emotion. It’s hard to tell, because other primates’ faces are covered by hair. (Interestingly, a recent paper suggests facial color communication is also used by some birds.)

Yet, in humans, nowhere else on the body are there so many blood vessels so close to the surface of the skin than our faces. The fact that we evolved much less facial hair than the apes suggests that our early ancestors may have found some advantage to letting their blushes show.

Humans just may be alone among primates for our ability to change facial color due to emotion.

What about fake blushes? Ones created with makeup?

“People have always said that we use makeup to look beautiful or younger, but I think that it is possible that we actually do it to appear happier or create a positive perception of emotion—or a negative perception, if you wanted to do that,” Martinez said.

Now that we know a little more about the varied colors of human facial expression, he suggested an intriguing new possibility: We could make “smart” cosmetics to play up certain emotions — or conceal them.

Rogue rouge aside, there are other applications for the technology. Researchers used what they learned to develop computer algorithms that could detect emotions via face color.

Given photographs of people expressing human emotion, the computer could match face color to feeling better than human study participants could. Happiness was the easiest for the computer detect: It had 90 percent accuracy. (“Fearfully disgusted” was the hardest emotion for it to catch onto, registering only 65 percent of the time.)

The findings may ultimately inform research in computer science, cognition, neuroscience and even human evolution.