Linear systems analysis of the vestibulo-ocular reflex: clinical applications

We used whole-body angular acceleration stimuli to estimate the transfer function of the vestibuloocular reflex in 20 normal subjects and several patients. Eye movements evoked by the stimuli were recorded and an adaptive nonlinear digital filter was used to extract the compensatory component of the eye-movement response. Frequency domain analysis of the stimulus and the compensatory component of the response was used to estimate the transfer function. The transfer function was estimated at 6 discrete frequencies (0.01 to 0.32 Hz by octaves) using individual sine-wave stimuli. Data from several patients with known lesions affecting the vestibular system were compared to the normal responses. Patients with a unilateral vestibular loss demonstrated low gains at frequencies below 0.02 Hz and large phase shifts below 0.32 Hz, but had normal responses at 0.32 Hz. Some of these same patients also exhibited a significant directional asymmetry in their responses.