Binocular eye movements evoked by self-induced motion parallax.

Perception often triggers actions, but actions may sometimes be necessary to evoke percepts. This is most evident in the recovery of depth by self-induced motion parallax. Here we show that depth information derived from one's movement through a stationary environment evokes binocular eye movements consistent with the perception of three-dimensional shape. Human subjects stood in front of a display and viewed a simulated random-dot sphere presented monocularly or binocularly. Eye movements were recorded by a head-mounted eye tracker, while head movements were monitored by a motion capture system. The display was continuously updated to simulate the perspective projection of a stationary, transparent random dot sphere viewed from the subject's vantage point. Observers were asked to keep their gaze on a red target dot on the surface of the sphere as they moved relative to the display. The movement of the target dot simulated jumps in depth between the front and back surfaces of the sphere along the line of sight. We found the subjects' eyes converged and diverged concomitantly with changes in the perceived depth of the target. Surprisingly, even under binocular viewing conditions, when binocular disparity signals conflict with depth information from motion parallax, transient vergence responses were observed. These results provide the first demonstration that self-induced motion parallax is sufficient to drive vergence eye movements under both monocular and binocular viewing conditions.

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