Optokinetic nystagmus and vestibular stimulation in squirrel monkey model.

Simultaneous application of the rotatory stimulus with a constant angular acceleration (1 degree/sec2) did not clearly improve the optokinetic pursuing ability in squirrel monkeys, even though the directions of vestibular and visual stimuli matched. When the directions of vestibular stimulus and visual stimulus conflicted, the optokinetic pursuing ability markedly declined regardless of the stimulus magnitude. The inter-individual difference was large in that situation. For the vestibular-visual coordination, the active head movement condition is considered to be natural and important as a biological function.