Induced motion and optokinetic afternystagmus: parallel response dynamics with prolonged stimulation.

Fixation of a stationary target during motion of background contours attenuates optokinetic nystagmus (OKN), while illusory induced motion (IM) of the fixated target occurs opposite the direction of contour motion. It is proposed that IM owes to a perceptually registered efferent signal for ocular pursuit which opposes an unregistered signal for OKN to achieve stable fixation. This proposal predicts parallel changes in the magnitudes of IM and optokinetic reflexes during and after optokinetic stimulation. Accordingly, leftward IM magnitude and rightward slow-phase velocity of optokinetic afternystagmus (OKAN) increased at similar rates across 90 and 160 sec of 60 deg/sec motion of background contours, and decayed at similar rates after stimulus termination. Both responses decayed more deeply following stimulation with, rather than without fixation. Neither retinal image motion nor vection can explain the IM obtained.