Effects of eccentric rotation on the human pitch vestibulo-ocular reflex

The pitch plane vestibulo-ocular reflex (VOR) gain and symmetry at low frequencies (< or =0.3 Hz) are enhanced by otoliths and/or somatosensory sensory cues during combined angular and linear stimuli. We conclude that neural processing of these linear motion cues is used to improve the VOR when stimulus frequencies are below the optimal range for the canals.

The purpose of this study was to examine the effects of eccentric rotation on the passive pitch VOR responses in humans.

Eleven subjects were placed on their left sides (90 degrees roll position) and rotated in the pitch plane about an earth-vertical axis at 0.13, 0.3, and 0.56 Hz. The inter-aural axis was either aligned with the axis of rotation (no modulation of linear acceleration) or offset from it by 50 cm (centripetal linear acceleration directed feet-ward). The modulation of pitch VOR responses was measured in the dark with a binocular videography system.

The pitch VOR gain was significantly increased and the VOR asymmetry was significantly reduced at the lowest stimulus frequencies during eccentric rotation. There was no effect of eccentric rotation on the pitch gain or asymmetry at the highest frequency tested.