When people sense danger, how quickly they react can mean the difference between life and death… and that reaction can occur in fractions of a second.
Researchers at Vanderbilt University in Nashville, Tennessee have been investigating the fear response. Psychology professor David Zald says they already know what parts of the brain respond to, say, the sight of a snake or the sound of an approaching speeding car.
He says they are the same parts of the brain that analyze facial expressions. "What appears to be happening is that the brain uses the same areas to detect a threatening stimulus as it does to detect if someone else is either threatening or feels scared," he explains, "because if someone's scared, you know there's something wrong in that environment. You need to pay attention to what's going on."
To determine how people knew whether someone else was frightened or not, Zald and his colleagues had subjects look at images of faces. Some faces had a fearful expression, some looked happy, and others were neutral.
The researchers found that their subjects could focus on the face with a fearful expression much more quickly than on a face that was neutral or happy. It seems the strongest clue comes from the eyes.
"The whites of the eyes are very high contrast… relative to the pupil," Zald explains. "And it's probably that some of these areas in the brain that are picking up on this first, very quickly, don't actually have a very strong representation of what they're seeing. What they have to work on is very limited information. And we think that high contrast nature of the eye is the sort of limited information that they can deal with."
Zald says this technique is a good way to examine the kind of information that people are processing unconsciously while they're paying attention to other things. He says their next step is to examine how people process other emotions.
His research will appear in the November 2007 issue of the journal Emotion.