Published in the June 6 issue of Science, the study reports that when viewing pictures of angry expressions, people exhibit more amygdala activity when the angry person in the picture is looking away. When viewing expressions of fear, the amygdala is more active when there is direct eye contact. This study is the first to demonstrate that gaze direction is an important signal in how we perceive facial expressions, according to the authors.
"Some people may be surprised to learn that the amygdala actually responded most when threat cues were ambiguous," said Reginald Adams, a former Dartmouth graduate student and the lead author on the paper. "This may indicate that the amygdala perceives heightened threat in uncertainty, or that the amygdala has to work harder to make sense of the ambiguity surrounding the threat."
For the study, participants viewed photographs of other people displaying anger and fear expressions. The eyes in the photographs were shifted to change the direction of the gaze. The participants' brain activity was captured with functional magnetic resonance imaging (fMRI).
The researchers report that the direction of gaze is important in determining whether the impending threat is coming from the person presenting the expression or from another dangerous element in the environment. The expressions of fear that were communicated eye-to-eye caused more amygdala activity as did averted expressions of anger, both of which suggest an uncertain source of threat or danger.
"This finding highlights the need for including eye gaze direction in future research examining how emotion is processed and perceived," said Adams.
The other authors on the paper include Heather Gordon, a Dartmouth graduate student; Abigail Baird, Assistant Professor of Psychological and Brain Sciences; Nalini Ambody, Associate Professor of Psychology at Harvard University; and Robert Kleck, Professor of Psychological and Brain Sciences.
This research was supported by a Doctoral Dissertation Improvement Grant from the National Science Foundation, and a National Research Service Award from the National Institute of Mental Health, both awarded to Adams. This study was also supported by a Dartmouth Reiss Family Senior Faculty Grant awarded to Kleck.