A mechanism for suppression of optokinesis.

We have studied optokinetic responses to oscillating patterns of dots, and the suppression of these responses by a foveally stabilized target. Such a target suppressed most of the optokinetic response, although the target provided neither retinal target motion nor target offset from the fovea. This indicates that suppression of OKN can occur by other means than smooth pursuit eye movements to traditional stimuli. We studied the form of the suppression for different optokinetic stimulus strengths and stimulus frequencies (0.25-1.0 Hz). The results show that over this frequency range the optokinetic response is substantial, and also that the suppression continues to operate. We also examined the time-course of suppression: it begins to appear within 150-200 msec of the appearance of a fixation target in motion relative to the optokinetic stimulus field.