We investigated the mechanism by which repetitive optic stimulation affects optokinetic responses. Eleven persons, physically healthy, took part in this study. The subjects were stimulated optokinetically to the right. The angular velocity of the Ohm type drum was 50 deg/sec, and the duration of the stimulation was 30 seconds. This stimulation was successively applied 5 times a day over a period of 3 weeks. Optokinetic nystagmus (OKN) was recorded with electronystagmography and analyzed with a computer. Before and during this trial, we did 2 tests every week. First, the drum was rotated with an angular acceleration of 2 deg/sec2, and optokinetic adaptation limit (OAL) was estimated. Next, the drum was rotated with an equal velocity of 40, 60 and 80 deg/sec. The initial rapid rise (IR), the maximum steady state slow phase velocity (SS) and the time constant of optokinetic afternystagmus (TC) were calculated. These items were evaluated with stimulation towards the right only in 5 subjects and with stimulation towards both the right and the left in 6 subjects.
Optokinetic training produced the following results : OAL increased significantly on stimulation towards the right, but did not increase on stimulation towards the left. SS increased significantly at a velocity of 60 and 80 deg/sec in both directions. IR increased significantly on stimulation toards the right, and increased slightly on stimulation towards the left. TC decreased on stimulation towards the right. We conclude that the increase of the slow phase velocity of OKN was due mainly to the enhanced function of the pursuit system, but other factors also had a role in training effects.