Reciprocal changes in primary and secondary optokinetic after-nystagmus (OKAN) produced by repetitive optokinetic stimulation in the monkey.

In six rhesus monkeys (Macaca mulatta) the effect of repetitive periods of whole-field optokinetic stimulation upon the different phases of optokinetic after-nystagmus (OKAN) was studied. The precedings optokinetic stimulus consisted of rotating a striped cylinder around the stationary monkey. Experiments were performed on up to 8 successive days. The results demonstrate that OKAN I and OKAN II are affected in a reverse manner by repeated optokinetic stimulation: The duration of OKAN I strongly decreases, whereas OKAN II increases in duration and intensity. The mechanisms under lying the generation of OKAN I and OKAN II and the role of OKAN II in the habituation process are discussed.