You can tell a lot more about a person's emotional state by looking at his or her body language, than by looking at the facial expression alone.

A new study shows that popular perception of faces falling in the sad or happy category isn't always true. Sometimes the difference in facial expression blurs leaving the viewer confused about what's really going on in a person's mind. This especially happens during a highly emotional event, like a sport. At these times, the brain follows body language cues, rather than facial expression to assess a person's state of mind.

"These results show that when emotions become extremely intense, the difference between positive and negative facial expression blurs. The findings, challenge classic behavioral models in neuroscience, social psychology and economics, in which the distinct poles of positive and negative valence do not converge," said Dr. Hillel Aviezer of the Psychology Department of the Hebrew University.

In the study, participants were shown photographs of people displaying intense emotions (very happy or very sad). Researchers used pictures of tennis players who either won or lost the match. When these participants were asked to rate the person's emotional state, their guesses fell in the realms of chance.

However, when these people were shown full length photographs of the people exhibiting the emotions, the participants' were almost always right. People were also more likely to assess the emotional states of others when only the picture of the body was shown. Interestingly, participants who saw a full body plus face picture felt that it was the facial expression that enabled them to judge a person's emotion. However, researchers say that this was due to "illusory valence," where the participants think they saw facial expression in an objectively non-diagnostic face.

Researchers also tested participant's ability at reading the emotional state of other people by showing them diverse pictures of people in real-life situations. The pictures ranged from joy (from a house makeover) to pain (getting a piercing) to grief (attending a funeral).

Viewers were unable to tell whether they were looking at pictures of positive emotions or negative ones. To further demonstrate that emotional facial expression are actually confusing, researchers "planted" faces on bodies that were displaying positive or negative emotions. Viewers rated the picture as happy or sad depending on the body language of the person in the morphed photograph.

Researchers say that the study shows how important body language is in human-interactions

"From a practical-clinical perspective, the results may help researchers understand how body/face expressions interact during emotional situations. For example, individuals with autism may fail to recognize facial expressions, but perhaps if trained to process important body cues, their performance may significantly improve," said Aviezer.

The study is published in the journal Science.