Perceptual, categorical, and affective processing of ambiguous smiling facial expressions

Why is a face with a smile but non-happy eyes likely to be interpreted as happy? We used blended expressions in which a smiling mouth was incongruent with the eyes (e.g., angry eyes), as well as genuine expressions with congruent eyes and mouth (e.g., both happy or angry). Tasks involved detection of a smiling mouth (perceptual), categorization of the expression (semantic), and valence evaluation (affective). The face stimulus display duration and stimulus onset asynchrony (SOA) were varied to assess the time course of each process. Results indicated that (a) a smiling mouth was visually more salient than the eyes both in truly happy and blended expressions; (b) a smile led viewers to categorize blended expressions as happy similarly for upright and inverted faces; (c) truly happy, but not blended, expressions primed the affective evaluation of probe scenes 550 ms following face onset; (d) both truly happy and blended expressions primed the detection of a smile in a probe scene by 170 ms post-stimulus; and (e) smile detection and expression categorization had similar processing thresholds and preceded affective evaluation. We conclude that the saliency of single physical features such as the mouth shape makes the smile quickly accessible to the visual system, which initially speeds up expression categorization regardless of congruence with the eyes. Only when the eye expression is later configurally integrated with the mouth, will affective discrimination begin. The present research provides support for serial models of facial expression processing.