Humans Have 21 Different Facial Expressions, Researchers Find

The Ohio State University researchers have categorized 21 different facial expressions. According to the team, humans can display a variety of compound expressions such as "happily surprised" or "sadly angry," and even contradictory expressions such as "happily disgusted".

The study is important because it helps scientists' understanding of emotions and facial expression. Until now, cognitive science researchers based studies on six basic expressions: happy, sad, fearful, angry, surprised and disgusted.

The computational model in the study will not only increase our understanding of how humans react to social cues, but is also expected to advance brain mapping systems and even help in the diagnosis of mental health conditions such as autism.

"We've gone beyond facial expressions for simple emotions like 'happy' or 'sad.' We found a strong consistency in how people move their facial muscles to express 21 categories of emotions," Aleix Martinez, a cognitive scientist and associate professor of electrical and computer engineering at Ohio State, said in a news release. "That is simply stunning. That tells us that these 21 emotions are expressed in the same way by nearly everyone, at least in our culture."

The study was based on tests on 230 volunteers. Participants were asked to make faces in response to certain cues such as "you smell a bad odor" ("disgusted") or "you just got some great unexpected news" ("happily surprised"). Researchers then analyzed 5,000 images and marked important facial muscles such as corners of the mouth.

The study team used Facial Action Coding System, or FACS, which is a standard tool in body language analysis. Researchers searched the database for similarities and differences in the facial expression.

The team found that there were 21 expressions including six basic ones that were different from each other.

Some common expressions were consistent, such as "happy" where people would stretch their mouths. Other expressions were a little contradictory such as 'happily disgusted," where people would scrunch up their nose and eyes while stretching their mouths.

According to the researchers, the identification of these "compound expressions," can help diagnose and treat people with mental disorders.

"For example, if in PTSD people are more attuned to anger and fear, can we speculate that they will be tuned to all the compound emotions that involve anger or fear, and perhaps be super-tuned to something like 'angrily fearful'? What are the pathways, the chemicals in the brain that activate those emotions? We can make more hypotheses now, and test them," Martinez said. "Then eventually we can begin to understand these disorders much better, and develop therapies or medicine to alleviate them."

The study is published in the journal Proceedings of the National Academy of Sciences.