Influence of head orientation on perceived gaze direction and eye-region information

Using synthetic 3D head and eye models, we examined the relationship between perceived gaze direction and the information within the image eye region across changes in head orientation. For each stimulus head and eye orientation, we rendered gray-scale images with realistic pigmentation and shading, and two-tone images depicting the regions corresponding to the iris, pupil, or eye-opening. Behavioural experiments using the gray-scale images as stimuli showed that perceived gaze direction was more strongly biased opposite to head orientation (repulsive effect) in the far-eye visible condition than in the near-eye visible condition. This trend occurred regardless of whether or not the whole face was visible, suggesting that the repulsive effect arose based on eye-region information. Consistent with this, geometrical analysis of the image eye region using the two-tone images revealed that the relative position of the iris and pupil of the far eye shifted opposite to head orientation more than that of the near eye. In addition, our findings regarding the pattern of the influence of head orientation suggest that estimation of the relative iris/pupil position may be achieved through a process of amodal completion of the whole iris behind the eyelid. Additional geometrical analysis of simulated images revealed situations where a greater repulsive effect for the far eye, as found here, is likely to be observed.