Abstract
Research indicates that people are remarkably good at discriminating where another person is looking (Gibson & Pick, 1963; Bock, Dicke, & Thier, 2008). Indeed, theories of human social attention are predicated on the idea that humans have developed an especially fine ability to use the eyes of others to make inferences about their attentional state (Kobayashi & Kohshima, 1997). Although this research demonstrates the importance of eyes to attention, little work has examined the specific mechanisms that underlie gaze discrimination itself. The prevailing view is that the discrimination of gaze direction relies on the use of the ratio of iris to sclera in the visible part of the eye (Gibson & Pick, 1963; Olk, Symons, & Kingstone, 2008). This theory is based on research that has used static images of eye direction. In real life, however, a change in eye position involves the motion of the eyes themselves as well as a change in the iris:sclera ratio. We examined the role of eye motion in the discrimination of eye movements. Participants were shown two eye images: eyes looking straight ahead and then eyes looking left or right at 1, 2 or 3 degrees visual angle from fixation. This resulted in the apparent motion of the eyes to the left or right. A 200 ms ‘blank screen’ preceded or followed these eye motion conditions. In the no-motion condition, the 200ms ‘blank’ display was inserted between the first and second eye image, eliminating the perception of motion. In all cases participants were required to judge eye direction and to rate how confident they were of their decision. Participants were more accurate and more confident of their judgements in the eye motion condition. These data suggest that motion information is used by the perceptual system to determine the direction of another individual's gaze.