Feedforward versus feedback modulation of human vestibular-evoked balance responses by visual self-motion information

Brian Day, MRC Human Movement Group, Sobell Department for Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, London

Abstract
Visual information modulates the balance response evoked by a pure vestibular perturbation (galvanic vestibular stimulation, GVS). Here we investigate two competing hypotheses underlying this visual-vestibular interaction. One hypothesis assumes vision acts in a feedforward manner by altering the weight of the vestibular channel of balance control. The other assumes vision acts in a feedback manner through shifts in the retinal image produced by the primary response. In the first experiment we demonstrate a phenomenon that is predicted by both hypotheses: the GVS-evoked balance response becomes progressively smaller as the amount of visual self-motion information is increased. In the second experiment we independently vary the pre-stimulus and post-stimulus visual environments. The rationale is that feedback effects would depend only upon the post-stimulus visual environment. Although the post-stimulus visual environment did affect later parts of the response (after ~400ms), the pre-stimulus visual environment had a strong influence on the size of the early part of the response. We conclude that both feedforward and feedback mechanisms act in concert to modulate the GVS-evoked response. We suggest this dual interaction that we observe between visual and vestibular channels is likely to apply to all sensory channels that contribute to balance control.

Not available

Back to Abstract