Updated on Friday, June 27, 2008, 00:00 IST

Melbourne, June 27: Understanding and interpreting facial expressions like anger, fear, happiness or sadness are evolutionary skills people have developed in order to survive.

But, a new study has revealed that facial expressions showing fear or anger are harder for the human brain to detect in crowds than individually or in small groups, even in those situations where people perceive there is a potential threat.

"As with anger, we perceive fear as a threatening emotion. That's because you don't always know the source of the fear. You can't determine whether it's because of you, or whether it's some larger threat.

"This study shows, that as humans, there is a limit to what we can automatically perceive and process," according to lead researcher Dr Mark Williams of Macquarie University in Australia.

In their study, Dr Williams and colleagues used functional magnetic resonance imaging or FMRI technology to measure activity in specific areas of the brain in real time to show which parts were active.

Study participants were shown multi-arrays of faces with happy, fearful and neutral expressions. They were told to identify the type of expression they saw. In the second part of the study, they had to search for particular expressions.

Bureau Report