FRIDAY, April 25 (HealthDay News) -- They say the eyes are a window into the soul, but scientists have been reporting for some time now that "microexpressions" -- lightning-fast, almost imperceptible facial expressions -- tell the real story of what people are thinking.

Now, new research suggests that people have a lot more trouble hiding their emotions than they think.

Canadian researchers found that every one of 41 college students suffered from "emotional leakage," the inability to hide their true feelings when asked to falsify their facial expressions. Some let their emotions out through subconscious expressions that lasted longer than microexpressions.

The findings suggest that "the face has enormous potential to reveal concealed and falsified emotions," said study co-author Leanne ten Brinke, a graduate student in experimental psychology at Dalhousie University in Halifax, Nova Scotia.

"Because the face is less controllable than other aspects of our non-verbal behavior, it is likely particularly important to lie detection," ten Brinke said.

Still, the researchers found that it's difficult even for trained experts to figure out when someone is hiding how they truly feel.

Microexpressions -- defined as lasting between 1/25th and 1/5th of a second -- have gotten attention in the media in recent years, but the study authors said there hasn't been extensive research into their existence. In the new study, published in the May issue of the journal Psychological Science, the study authors tried to coax unconscious expressions out of college students participating in the research project.

The participants -- 35 females and six males -- watched a series of images, with some designed to elicit an emotion from the viewer, such as happiness (puppies playing) or disgust (a severed hand). Some images (like a picture of a truck) were designed to elicit a neutral response.

The researchers videotaped the participants and their reactions, compiled images of about 700 emotional expressions, and assigned "coders" to examine about 100,000 frames.

"While our research did detect several microexpressions, leakage of unintended emotions typically lasted longer," ten Brinke said. "We found that when a lying participant's face revealed unintended emotions, it typically lasted for closer to a second but usually only occurred in either the upper or lower face."

Dr. Daniel Langleben, an assistant professor of psychiatry at the University of Pennsylvania, said brief and revealing but unconscious facial expressions do appear to be a real phenomenon, although it's difficult for people to detect them. Computers, he said, may do a better job.

"A computer that looks [at a face] using facial-recognition software doesn't care if it's red, black, white or green or whether it reminds you of your grandmother or if the face is ugly or pretty," he said.

Ten Brinke said the next step is to create research that better reflects real life by studying emotional deceptions that could have serious consequences.

The Canadian researchers have collected about 60 videotaped appeals from family members pleading to the public for the return of their missing relatives. In about half of the cases, the people in the videotapes actually killed the relatives, she said.

"We will be examining the faces of these individuals for cues to deceit in this real-life context," ten Brinke said.

More information

Learn more about facial expressions from Carnegie Mellon University.