Optokinetic and vestibulo-ocular reflex responses to an unpredictable stimulus.

Horizontal plane optokinetic (OKR) and vestibulo-ocular reflex (VOR) eye movements were obtained from normal subjects in response to pseudorandom rotational stimulation. Results showed large intersubject variability in OKR responses. Typical OKR responses had approximately constant gain (Mean 0.65) over 0.02-1.5 Hz. Response phase was near zero below 0.1 Hz with increasing phase lags as frequency increased consistent with time delays of 180 ms (Mean value). Variations in OKR responses included declining gains with increasing frequency and phase lags consistent with time delays of 90 to 268 ms. Significant interactions of visual and vestibular motion information were detected at the highest stimulus frequency at which both were tested (1.5 Hz). Results suggested that visual motion information could be significant in the control of eye movements up to 6.1 Hz. Pseudorandom optokinetic stimulation induced motion sickness symptoms in approximately 20% of 213 subjects tested. Pseudorandom vestibular stimulation of twice the amplitude and duration did not initiate motion sickness symptoms in any subject.