Characterization of vestibulo-ocular reflex dynamics : responses to head perturbations during gaze stabilization versus gaze redirection

In this study, we compare VOR response dynamics induced by high-frequency (>5 Hz) passive head-on-body perturbations, applied during gaze stabilization versus gaze redirection. During gaze stabilization, we first rotated the heads of three Rhesus monkeys over the frequency range 5--25 Hz. The VOR was compensatory across all frequencies tested; mean gains (eye velocity/head velocity) were near unity, with phase lag increasing only slightly with frequency. Transient perturbations ≥80 Hz were then used to further probe VOR dynamics. During periods of gaze stabilization, VOR response latency to the transient perturbations was 5--6 ms, and mean gain induced was near unity for two of the three animals tested. The same perturbations were then applied at different intervals before, during and following 15°, 40° and 60° gaze shifts. The VOR elicited was generally attenuated compared to that evoked during gaze stabilization, and the level of suppression tended to decrease with time from gaze shift onset. We conclude that models for the control of gaze should be modified to account for the time course of VOR gain changes during gaze shifts