Abstract
The eyes of others play a crucial role in social interactions, providing information such as the focus of another’s attention, their current thoughts and emotions. Although much research has focussed on understanding how we perceive gaze direction, little has been done on gaze vergence, i.e. the angle between the two eyes. The vergence of the eyes yield potential information about the distance of another’s fixation – the more converged someone’s eyes are, the closer their object of fixation. We recently reported a systematic bias to perceive gaze as convergent, especially when gaze was directed downwards compared to upwards (Nguyen, Palmer, Otsuka and Clifford, 2018). In the present study, we aimed to determine the fixation distance at which participants perceive a face to be gazing in a stereoscopically simulated three-dimensional environment. Participants were presented with synthetic faces gazing at varying fixation distances and asked to indicate on which one of 10 small spheres the avatar was fixating. The data revealed a systematic underestimation of fixation distance for downwards-averted gaze as well as a limit in discrimination of gaze vergence beyond 35cm. When the faces were inverted, fixation distance was again underestimated for gaze vergence in the observer’s lower visual field, this time corresponding to the avatar’s upwards gaze. This pattern of results indicates that our bias to underestimate others’ fixation distance relies more on our own internal sense of up and down than on that of the other person.