WEDNESDAY, Nov. 19 (HealthDay News) -- Did you just get shot down by a co-worker who has no interest in going on a date? Look at the bright side: New research suggests that rejection may boost your ability to detect insincere smiles.

People who were thinking about being rejected recognized 80 percent of fake human smiles shown on a computer monitor, the study found. By comparison, other study participants were only able to detect insincere smiles about half of the time.

It's not clear why rejection may boost the ability to figure out when someone else is faking an emotion. It may have something to do with a primitive need to fit in with others and to detect what they're really thinking, said study lead author Michael Bernstein, a graduate student at Miami University in Ohio.

"People who are rejected have got to be really concerned about getting back into a group," he said.

Humans can easily fake smiles when they aren't feeling any positive emotions. Detecting an insincere smile isn't easy, however, although there are clues if you look closely, Bernstein said.

"A real smile is an automatic process. It involves muscles that are not involved when you make a fake smile," he said. "All smiles involve muscles around the mouth, but only real smiles involve muscles around the eye."

A real smile indicates signs that someone wants to work with another person and cooperate, Bernstein said. "With a fake smile, you might be feeling good and wanting to cooperate, but you might be hiding something."

Mark Frank, director of the Communication Science Center at the University of Buffalo, thinks people may not want to fully understand other people's motivations as expressed through their facial expressions.

"This is a consequence of living in polite society -- we do not 'peek behind the scenes' of what someone is really feeling in most of our polite discourse," he said. "In other words, being polite means seeing someone as they want to be seen, maybe not how they actually are."

For the new study, Bernstein and his colleagues asked 17 women and 15 men, all undergraduate students, to watch a video of people smiling. Some of the smiles were fake.

Some of the participants were told to remember a time when they felt "rejected or excluded." Others were instructed to think about a time when they felt "accepted or included," or simply recall what they did that morning.

Those who thought about being rejected were most likely to detect fake smiles; those in the other groups performed at about the same level.

"We think the reason why this happens is that being rejected is a very dangerous situation to be in," Bernstein said. "You're in a precarious state. You're without a group. From an evolutionary perspective, that's an extremely dangerous place to be."

Those who are rejected may be more careful about finding a new group to belong to and become more perceptive, Bernstein added.

Frank said the new study falls into a category of research that aims to understand human emotions.

"From a practical point of view, it has some implications for helping us understand why people make some of the choices they do, when they may seek out others, and when they may reject others, even if it may not be in their long-term interests to do so," he said.

The study was published in the October issue of the journal Psychological Science.

More information

For more on human emotions, visit the Argosy University.