Geometrical basis of perception of gaze direction.

Perception of gaze direction depends not only on the position of the irises within the looker's eyes but also on the orientation of the looker's head. A simple analysis of the geometry of gaze direction predicts this dependence. This analysis is applied to explain the Wollaston effect, the Mona Lisa effect, and the newly presented Mirror gaze effect. In an experiment synthetic faces were used in which the position of the iris and the angle of head rotation were varied. Different groups of subjects judged iris position, head rotation, and gaze direction of the same stimuli. The results illustrate how cues of iris location and head orientation interact to determine perceived gaze direction.