In human subjects optokinetic spinal reflexes, nystagmus and vertigo are induced by optokinetic stimulation. Responses induced by the rotation of an Ohm-type cylinder (2m in diameter and 2m in height) were studied in human adults.
Experiment A. The cylinder was rotated with a constant angular acceleration of 2°/sec² for 90 seconds. The subject was instructed to step in place at the center of the cylinder while looking at its moving stripes. When the cylinder speed was slow, the angle of stepping deviation was small, and vertigo was not present. When the stimulus speed was fast, the slow phase of eye speed was slower than the movement of the stripes, the subject complained of vertigo and the angle of stepping deviation increased.
Experiment B. The cylinder was rotated with a constant angular acceleration of 1°/sec² or 4°/sec². Changes in the angular acceleration of optokinetic stimulation showed no differences in the patterns of responses.
Experiment C. The subject was instructed to step in place at the center of the cylinder carefully watching an otogoniometer. Optokinetic nystagmus was suppressed. When the cylinder velocity was slow, the angle of stepping deviation was larger with than without the otogoniometer.
Experiment D. Optokinetic stimulation was provided by double cylinders. The outer cylinder was an Ohm-type cylinder, and the inner cylinder had 12 visual targets. The subject was instructed to follow the targets of the inner cylinder. Stepping deviation was induced by the outer cylinder. There was little or no vertigo.
Experiment E. The changes of responses induced by repeated optokinetic stimulation (optokinetic training) were studied. The subject was trained daily for 3 weeks. After a 2 week interval the training was repeated for 2 more weeks. Optokinetic training resulted in a decrease of stepping deviation, an increase of optokinetic nystagmus and tolerance to optokinetic vertigo. Thus, training results in an increased adaptability to optokinetic stimulation.