Evaluating Faces on Social Dimensions
People automatically evaluate faces on multiple trait dimensions and these evaluations predict important social outcomes ranging from electoral success to sentencing decisions. Based on behavioral studies and computer modeling, we identify two orthogonal dimensions - valence and dominance - that underlie evaluation of emotionally neutral faces and show that a) these dimensions can be approximated by judgments of trustworthiness and dominance; b) whereas the valence dimension is sensitive to features resembling expressions signaling approach / avoidance behavior, the dominance dimension is sensitive to features signaling physical strength / weakness; and c) judgments such as threat can be reproduced as a function of these two dimensions. The findings suggest that face evaluation is an overgeneralization of adaptive mechanisms for inferring harmful intentions and the ability to cause harm. In a series of functional neuroimaging studies, we show that valence evaluation of faces involves the amygdala and inferotemporal cortex. The amygdala is engaged even when the subjects' task does not demand person evaluation, suggesting that faces are automatically evaluated in term of their valence. The more negative the face is, the stronger the amygdala response is. The extent to which specific trait judgments such as trustworthiness, threat, and dominance predict the amygdala response is perfectly predicted by the amount of variance these judgments share with the general valence evaluation of the face. We also identify conditions under which the amygdala's response to face valence is non-linear. We are currently investigating the neural basis of dominance evaluation.
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