A Quantitative Study of Vestibular Adaptation in Humans

Abstract

A mathematical model for short-term adaptation to vestibular stimuli is presented. A transfer function is derived relating slow phase angular velocity of resulting nystagmus to the angular velocity of head rotation. The resulting model has been tested by comparing its responses to controlled step and ramp angular velocity stimuli with those of 8 human subjects, and in all cases a close match was obtained. The mean time constant of the adaptive term was 82 sec (S.E.±6.5) and the mean cupular restoration time constant (T_c) was 21 sec (S.E.±1.5). It is suggested that previous values quoted for T_c represent underestimates of the true value owing to superposition of the adaptive term here described. The adaptive term accounts well for the phenomenon of secondary nystagmus, especially during either strong stimuli or prolonged rotations. Some implications of the findings in relation to clinical and aviation medicine are discussed.