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New research has found that the brain processes images of fearful faces faster than images of neutral or happy faces, according to a study by Vanderbilt reasearchers.
“There are reasons to believe that the brain has evolved mechanisms to detect things in the environment that signal threat. One of those signals is a look of fear,” says David Zaid, co-author (along with Eunice Yang and Randolph Blake) of the new study. It will appear in the November 2007 issue of Emotion.
Researchers set out to determine if we become aware of fearful, neutral or happy expressions at the same speed, or if one of those expressions reaches our awareness faster than the others. Because humans process facial information in less than 40 milliseconds, researchers had to find a way to slow down the speed at which subjects process it.
Yang, the lead author, realized that a technique being used in Blake’s lab might be a solution. The technique, continuous flash suppression, keeps people from becoming aware of what they are seeing for up to 10 seconds. Using this technique, the team had research subjects look at a screen through a viewer, similar to the eyepieces of a microscope, which allowed different images to be presented to each eye.
Many images were rapidly presented to one eye while a static image of a face was presented to the other. The multiple images served as visual “noise”, suppressing the image of the face. The subjects indicated when they first became aware of seeing a face, enabling the researchers to determine if the expression on the face had any impact on how quickly the subject became aware of it.
The subjects became aware of faces that had fearful expressions before neutral or happy faces, the team found. They believe a brain area called the amygdala, which shortcuts the normal brain pathway for processing visual images, is responsible.
“The amygdala receives information before it goes to the cortex, which is where most visual information goes first. We think the amygdala has some crude ability to process stimuli and that it can cue some other visual areas to what they need to focus on, said Zaid.
Zaid and his colleagues believe the eyes of the fearful face play a key role. “Fearful eyes are a particular shape, where you get more of the whites of the eye showing,” he said. “That may be the sort of simple feature that the amygdala can pick up on, because it’s only getting a fairly crude representation. That fearful eye may be something that’s relatively hardwired in there.”
A surprising finding was that subjects perceived happy faces the slowest.
“What we believe is happening is that the happy faces signal safety. If something is safe, you don’t have to pay attention to it,” said Zaid.
Next researchers will explore how this information influences our behavior. “We are interested in exploring now what this means for behavior,” said Yang. “Since these expressions are being processed without our awareness, do they affect behavior and decision making? If so, how?”
The research was funded by the National Institutes of Health. Blake and Zaid are investigators at the Vanderbilt Kennedy Center for Research on Human Development.
source: www.sciencedaily.com; adapted from material provided by Vanderbilt University.
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