Quantitative analysis of the human visual vestibulo-ocular reflex in sinusoidal rotation

In order to investigate interaction of the vestibular and optokinetic system, a visual vestibulo-ocular reflex (V-VOR) gain in forty-five normal subjects was measured by manual and computer analysis. The test subjects sat in a newly devised, pendular rotating chair in an optokinetic drum. With this device pendular harmonic sinusoidal rotation and optokinetic stimuli could be given simultaneously. The test subjects were rotated sinusoidally at amplitudes of 120 degrees and 240 degrees and at frequencies of 0.05 Hz and 0.1 Hz (maximum velocities 18.8 degrees/s, 37.7 degrees/s, 75.4 degrees/s), and with eyes closed and open. Within these pendular stimuli, there was no response decline phenomenon nor influence of amplitude on frequency. The pure VOR gain measured in dark room with eyes open was about 0.6 and did not vary with the eyes closed as long as mental alertness was maintained. The V-VOR gain in a stationary optokinetic drum with eyes open was about 1.1. From our observations, the 0.1 Hz sinusoidal rotation with an amplitude of 240 degrees (maximum velocity, 75.4 degrees/s) is an appropriate stimulation for the V-VOR and VOR test battery in clinical practice.