Human spontaneous gaze patterns in viewing of faces of different species.

Clear differences in perceptual and neural processing of faces of different species have been reported, implying the contribution of visual experience to face perception. Can these differences be revealed by our eye scanning patterns while we extract salient facial information? Here, we systematically compared non-pet-owners' gaze patterns while exploring human, monkey, dog, and cat faces in a passive viewing task. Our analysis revealed that the faces of different species induced similar patterns of fixation distribution between left and right hemiface, and among key local facial features, with the eyes attracting the highest proportion of fixations and viewing times, followed by the nose, and then the mouth. Only the proportion of fixations directed at the mouth region was species-dependent and could be differentiated at the earliest stage of face viewing. Our spontaneous eye-scanning patterns associated with face exploration appear to have been mainly constrained by general facial configurations; the species affiliation of the inspected faces had limited impact on gaze allocation, at least under free-viewing conditions.