Short-latency primate vestibuloocular responses during translation

Short-lasting, transient head displacements and near target fixation were u sed to measure the latency and early response gain of vestibularly evoked e ye movements during lateral and fore-aft translations in rhesus monkeys. Th e latency of the horizontal eye movements elicited during lateral motion wa s 11.9 +/- 5.4 ms. Viewing distance-dependent behavior was seen as early as the beginning of the response profile. For fore-aft motion, latencies were different for forward and backward displacements. Latency averaged 7.1 +/- 9.3 ms during forward motion (same for both eyes) and 12.5 +/- 6.3 ms for the adducting eye (e.g., left eye during right fixation) during backward mo tion. Latencies during backward motion were significantly longer for die ab ducting eye (18.9 +/- 9.8 ms). Initial acceleration gains of the two eyes w ere generally larger than unity but asymmetric. Specifically, gains were co nsistently larger for abducting than adducting eye movements. The large ini tial acceleration gains tended to compensate for the response latencies suc h that the early eye movement response approached, albeit consistently inco mpletely, that required for maintaining visual acuity during the movement. These short-latency vestibuloocular responses could complement the visually generated optic flow responses that have been shown to exhibit much longer latencies.