Illusory facial expressions caused by lighting direction

Journal of Experimental Psychology: General
Ramanathan, Mahith; Peterson, Lindsay M.; Palmer, Colin J.

Our daily interactions draw on a shared language of what facial expressions mean, but accurate perception of these signals may be subject to the same challenges that characterize visual perception in general. One such challenge is that faces vary in their appearance with the context, partly due to the interaction between environmental lighting and the characteristic geometry of the human face. Here, we examine how asymmetries in lighting across the horizontal and vertical axes of the face influence the perception of facial expressions in human observers. In Experiment 1, we find that faces with neutral expression appear to bear a negatively valenced expression and appear higher in emotional arousal when lit from below—an illusion of facial expression where none really exists. In Experiment 2, we find that faces performing common emotional expressions are more often miscategorized when lit from below compared to when lit from above, specifically for angry and neutral expressions. These data show that changes in facial appearance related to illumination direction can modify visual cues relevant to social communication—and suggest that facial expression recognition in humans is partially adapted to (naturalistic) environments in which light arrives predominately from overhead.