Unilateral habituation of vestibulo-ocular responses in the cat

Vestibulo-ocular reflex as a parameter of seasickness susceptibility

The vestibulo-ocular reflex (VOR) is known to be modulated in response to changing vestibular and optokinetic stimuli. The purpose of this study was to investigate possible relationships between VOR and future susceptibility and habituation to seasickness. Thirty candidates for future maritime service were exposed to a series of yaw axis smooth harmonic accelerations before and after 6 months of regular sailing, and their VOR gain and phase responses were recorded. Seasickness severity was estimated after 1 and 6 months of service by a questionnaire. We conclude that VOR gain at 0.01 Hz may serve as a physiologic correlate helping to predict seasickness susceptibility, and that the increase in phase lead at 0.02 Hz may mark the habituation process to sea conditions.

The significance of attention and duration of the stimulation in optokinetic nystagmus

Twenty normal human subjects were exposed to horizontal optokinetic stimulation of (OKN) of one minute's duration. They were instructed either to look attentively at every passing target or to stare unattentively at the moving field. After one week the tests were repeated. Another group received optokinetic training for 10 days. It is concluded that arousal is of decisive importance for the reproducibility of OKN. Diversion of the attention did not cause a change in the neural path from a cortical to a subcortical predominance. The estimate of the velocity of the slow phase (EV) must be based on a sufficiently long period of stimulation. The maximum EV of individual beats was not representative of inattentive OKN. The training effect of OKN was short-lasting and insignificant.

Vestibular habituation in man and monkey during sinusoidal rotation

Habituation of the vestibular system by repeated steps of angular velocity leads to a shortening of nystagmus. These steps can be broken down into different frequency sinusoids. High-frequency sinusoidal rotation (above 0.1 Hz) generally was found to be ineffective, while low-frequency stimulation (0.0015-0.05 Hz) led to a dramatic shortening of time constants after only a few cycles of stimulation. In the alert monkey, time constants of vestibular nystagmus and single units, recorded from the vestibular nuclei, are always similar and covary together. Experiments in humans, with measurement of nystagmus and subjective velocity sensation, suggest similar processes for habituation.