“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,” David Zald, associate professor of psychology and a co-author of the new study, said. “We believe that the brain can detect certain cues even before we are aware of them, so that we can direct our attention to potentially threatening situations in our environment.”

Researchers set out to determine if we become aware of fearful, neutral or happy expressions at the same speed, or if one of these expressions reaches our awareness faster than the others.

The team found that subjects became aware of faces that had fearful expressions before neutral or happy faces. They believe a brain area called the amygdala, part of the emotions-processing limbic system, shortcuts the normal brain pathway for processing visual images.

“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,” Zald said.

Zald 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.”

“We are interested in now exploring what this means for behavior,” Yang said. “Since these expressions are being processed without our awareness, do they affect our behavior and our decision making? If so, how?”

The research was supported by funding from the National Institutes of Health. Blake and Zald are Vanderbilt Kennedy Center for Research on Human Development investigators. Randolph Blake, Centennial Professor of Psychology, and Eunice Yang, doctoral student, were co-authors of the study, which appeared in the November 2007 issue of Emotion.