Two types of response property in otolith-optokinetic interaction.

Otolithic influence on optokinetic eye-movements (visual-vestibular interaction) was investigated using oscillation of a lateral linear acceleration-step combined with optokinetic stimulation. According to our preliminary study using a 40-deg/s optokinetic stimulus speed at 0.3 and 0.5 G acceleration-steps, the interaction was characterized by a linear addition during the agonistic stimulus condition, but by suppression of the otolith-ocular reflex during the antagonistic stimulus condition. In the present study, we further examined the interaction using 3 different optokinetic speeds at an acceleration step of 0.3 G. It was revealed an additional type of response property that was characterized by marked elevation in the eye velocity with increase in the optokinetic stimulus speed, probably due to the gain increase in the optokinetic response velocity. In either type of the response property, however, the interaction seemed to be nonlinear in the otolith system, being in contrast to linear interaction postulated for the semicircular canal system.