Modification of per- and postrotational responses by voluntary motor activity of the limbs.

In order to explore interactive effects of voluntarily generated rotational stimuli on evoked vestibular responses, experiments were performed using a rotation chair in which the subject either controlled the angular motion by voluntary movement of his upper and lower limbs, or was passive-rotation being controlled by a servomotor and electromagnetic brake. In two experiments, carried out on 8 and 9 subjects respectively, it was found that cessation of sustained passive rotation by voluntary limb actions strongly suppressed the postrotational turning sensation but did not alter the evoked nystagmus. Limb movements that were directionally concordant with muscle torque in generating body rotation yielded arthrokinetic effects which augmented perrotational nystagmus and sustained the sensation of turning. The postrotational sensation of turning and postrotational nystagmus produced by voluntary cessation of active rotation were reduced relative to responses produced by passive turning and stopping. The Purkinje effect induced by postrotational head movements was similarly reduced following voluntary cessation of active rotation.