Otolithic-acoustic interaction in the control of eye movement

In order to examine otolithic contribution to eye movement, 10 subjects were asked to track either a moving acoustic target or a still target during subject linear motion on a cart. The relative displacement between subject and target was the same in the two situations. Eye movement during subject lateral acceleration in the dark without any task, or with the task of tracking an imagined still target were recorded as control. Motion frequency ranged 0.15-0.3 Hz, with peak acceleration of 0.55-1.2 m/s/s. Only saccdic eye movements (EM) were recorded during the tracking of a moving acoustic target. Slow EM interspersed by saccades were observed when a moving subject was tracking an imagined or an acoustic stationary target. Contribution of slow phases to tracking was more important in the presence of an acoustic than an imagined target. The results can be interpreted in terms of either otolithic contribution to the central reconstruction of target velocity, or adaptive control of otolith-ocular reflex gain. A conceptual model accounting for these interpretations is presented.