They love to make you mad

"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, University of Michigan associate professor of psychology.

His study may explain why some people like to tease each other, he said.

"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."

Schultheiss and Michelle Wirth used saliva samples to measure testosterone levels in participants, who then worked on a series of computer tasks that were followed by angry, neutral or no face on the screen. Participants who were high in testosterone, which has been associated with dominance motivation, learned the sequence that was reinforced by the angry face, said the researchers, whose work was published in the journal Physiology and Behavior.

Copyright 2007 by United Press International