The influence of visual input on the vestibulo-ocular reflex.

In order to stabilise a fixation target on the retina, eye movements have to compensate for head movements. During slow head movements visual feedback can control these eye movements. During fast movements of the head, mainly the vestibulo-ocular reflex (VOR) controls eye movements, as visual feedback is too slow. However, visual feedback is an important factor in controlling the VOR; e.g. the gain of the VOR depends on the distance of the target. This study investigates the influence of retinal image position during fast head movements. The experiments were carried out in five human subjects using scleral search coils. The adaptation of each eye individually to a change of retinal position of a target was examined during head shaking. The change in visual input was carried out by placing Fresnel prisms of different strengths in front of both eyes, thus inducing a change in retinal image position without changing the retinal slip. The results show, that both eyes make the appropriate corrections when the visual input changes, even during fast head-movements. These corrections did not influence the gain of the VOR. From these results we conclude, that retinal image position besides retinal slip has a major influence on the monocular eye movements even at high head rotation frequencies.