Perception of eye positions

Abstract

In a two-alternative forced-choice psychophysical test human subjects were tested for their ability to perceive their own viewing direction. A small red flash was presented at different horizontal positions left or right from the subjects' eye position on the screen. Eye positions were recorded with an Eyelink infrared system at 250 Hz temporal resolution. Subjects had to indicate whether the flash on the screen occurred left or right of their own eye position. The task was performed during different viewing conditions -- fixation or free viewing -- and different background stimulation--a static black screen or moving random dots. The results show that, during the fixation task, subjects perceive their eye position very accurately, with performance reaching the 75% correct level for deviations well below a degree of visual angle. During free viewing on a dark background, the accuracy was much less, and a small bias for left or right choices in some subjects was observed. No consistent bias was observed for leftward or rightward moving backgrounds.