Vergence nystagmus induced by motion in the ground plane: normal response characteristics.

We displayed backward/forward motion on a computer monitor in the ground plane. Subjects looked at the center of a moving pattern and eye movements of both eyes were recorded with a search coil system. Involuntary nystagmus including vertical version (VV) and horizontal vergence (HV) was recorded. Dynamics of the nystagmus showed that the slow and quick phase of VV and HV were always associated with each other while the monocular horizontal eye movements composed of HV were either symmetrical or asymmetrical. Peak velocity, amplitudes and frequency of the VV and HV responses were quantified. The results suggest that involuntary HV nystagmus can be induced by simple motion from simulated optic flow in the ground plane and the HV nystagmus helps moving subjects to stabilize their gazes on the object of interest.