Most people don't appreciate an angry look, but a new University of Michigan psychology study found that some people find angry expressions so rewarding that they will readily learn ways to encourage them.

"It's kind of striking that an angry facial expression is consciously valued as a very negative signal by almost everyone, yet at a non-conscious level can be like a tasty morsel that some people will vigorously work for," said Oliver Schultheiss, co-author of the study and a U-M associate professor of psychology.

The findings may explain why some people like to tease each other so much, he added. "Perhaps teasers are reinforced by that fleeting 'annoyed look' on someone else's face and therefore will continue to heckle that person to get that look again and again," he said. "As long as it does not stay there for long, it's not perceived as a threat, but as a reward."

The researchers took saliva samples from participants to measure testosterone, a hormone that has been associated with dominance motivation.

Participants then worked on a "learning task" in which one complex sequence of keypresses was followed by an angry face on the screen, another sequence was followed by a neutral face, and a third sequence was followed by no face.

Participants who were high in testosterone relative to other members of their sex learned the sequence that was followed by an angry face better than the other sequences, while participants low in testosterone did not show this learning advantage for sequences that were reinforced by an angry face.

Notably, this effect emerged more strongly in response to faces that were presented subliminally, that is, too fast to allow conscious identification. Perhaps just as noteworthy, participants were not aware of the patterns in the sequences of keypresses as they learned them.

While high-testosterone participants showed better learning in response to anger faces, they were unaware of the fact that they learned anything in the first place and unaware of what kind of faces had reinforced their learning.

Michelle Wirth, the lead author of the study and now a postdoctoral researcher at the University of Wisconsin, Madison, added: "Better learning of a task associated with anger faces indicates that the anger faces were rewarding, as in a rat that learns to press a lever in order to receive a tasty treat. In that sense, anger faces seemed to be rewarding for high-testosterone people, but aversive for low-testosterone people."

She said the findings contribute to a body of research suggesting that perceived emotional facial expressions are important signals to help guide human behavior, even if people are not aware that they do so.

"The human brain may have built-in mechanisms to detect and respond to emotions perceived in others," she said. "However, what an emotional facial expression, such as anger, 'means' to a given individual—whether it is something to pursue or avoid, for example—can vary."

U-M psychology researchers Michelle Wirth and Schultheiss, the authors of the study, published their findings in the journal Physiology and Behavior.