Binocular eye movements caused by the perception of three-dimensional structure from motion

We report that the perception of three-dimensional structure from monocular two-dimensional images changing over time--the kinetic depth effect (KDE)--can evoke binocular eye movements consistent with a three-dimensional percept. We used a monocular KDE stimulus that induced a vivid perception of a rigid three-dimensional sphere rotating in space. The gaze directions of both eyes were measured while observers pursued the motion of a patch on the surface of the perceived sphere as it went through a complete revolution. We found that the eyes converged when the patch was perceived on the front surface of the KDE sphere and diverged when the patch was perceived in the back. The pattern, magnitude and dynamics of binocular eye movements observed in the KDE experiment resembled those obtained when subjects viewed binocularly a light-emitting diode (LED) rotating in space and to the responses obtained with a dynamic stereogram simulating a rotating random dot sphere. Thus, the perception of three-dimensional structure from motion, stereopsis, or motion and stereopsis combined, were effective in guiding binocular eye movements.