OKN and OKAN induced by stripe and random dot patterns

Abstract

The velocity storage mechanism in optokinetic nystagmus (OKN) was studied in 50 healthy adults. We used stepwise stimulations generated by projecting stripe and numerous random dot patterns on a screen at 20, 40, 60 and 80 deg/sec. The slow-phase OKN velocity followed stripe and random dot patterns almost immediately after the onset of the stimuli at 20 deg/sec. On the other hand, it tended to gradually increase after the onset of stimuli at 60 or 80 deg/sec. This gradual increase in slow-phase eye velocity has also been observed in several animal species, such as the monkey and cat. The slow-phase velocity of the first OKAN beat was higher with the random dot pattern than with the stripe pattern regardless of stimulation velocity. The above findings indicate that OKN in man is mediated through direct and also indirect pathways as observed in animals. With random dot pattern stimulation, particularly, the indirect pathway seems to perform an important role in generating OKN and OKAN.