Gaze perception under vertical asymmetries in illumination

Strong lighting from above is common in everyday environments and this statistical regularity has shaped the function of the human visual system. Here we investigate the influence of vertical asymmetries in illumination on the perception of gaze direction, a ubiquitous social cue that we derive from the appearance of another person's face and which provides an important input to social cognition by conveying the focus of that person's attention. We find that changes in the appearance of the human face that result from changes in vertical lighting direction cause a systematic shift in the apparent angle of gaze, reflected in judgments that observers make about eye contact. Moreover, the perception of gaze direction under vertical asymmetries in illumination relies strongly on perceptual constancy mechanisms, namely an implicit sensitivity of the visual system to the lighting context when computing gaze direction from the appearance of the eyes. Perceptual constancy in gaze perception operates robustly both when viewing faces lit from above and faces lit from below, though a reliance on cues to the lighting direction is particularly apparent when observers report the vertical gaze direction of faces lit from below. These results illustrate how differences in the appearance of the human face across changes in the lighting conditions can influence the perception of social cues, and the importance of perceptual constancy mechanisms in visual processing for maintaining a relatively robust sense of other people's gaze direction despite asymmetries in lighting that typically occur in everyday environments.