On the interaction of vestibular and optokinetic nystagmus in man.

The interaction of vestibular and optokinetic nystagmus (OKN) was investigated by applying periods of ipsi- and contradirectional optokinetic stimulation during perand postrotatory vestibular nystagmus in healthy humans. Slow phase velocity and cumulative eye displacement of OKN was enhanced by vestibular nystagmus beating in the same direction of decreased by contradirectional vestibular nystagmus. A distinct correlation between the intensity of vestibular stimulation and the modification of OKN could be demonstrated by averaging the responses obtained in different subjects. On the other hand there was also a modification (enhancement or decrease) of vestibular nystagmus slow phase velocity by preceding OKN. Considering the intensity of these modifications, large interindividual differences were observed.