The right eye for fixations: Eye asymmetries modulate gaze patterns towards speakers.

Eye contact is critical in face-to-face social interactions. Prior research has shown that dialog partners primarily focus on the eyes of the speaker both when the speaker is speaking and, particularly, when the speaker is not. These findings are compatible with the communicative but specifically the social function of eye contact. This is in line with animal cognition literature showing that animals with more eye sclera tend to be more social. Several human studies have reported a left perceptual bias in eye contact, with the listener focusing on the right side of the speaker's face. Some studies attributed this bias to hemispheric specialization. Here two eye-tracking experiments using human and virtual human speakers confirmed a systematic bias towards the right eye of the speaker. Findings, however, are modulated by the amount of sclera and communicative events. Larger eyes (more sclera visibility) attracted more fixations, so that faces with larger left eyes do not systematically induce the left perceptual bias to the right side of the face. Moreover, a difference in fixations on the left or right eye of the speaker was found depending on whether somebody was speaking or not. Our results are consistent with the left perceptual bias, but suggest the bias is not solely perceptual. Instead, our findings suggest the social function in eye contact modulates the bias towards the right eye. Face-scanning behavior emerges as an unfolding dynamic shaped by a flow of social and communicative action ladders. These findings shed light on the most fundamental aspects of human communicative behavior.