title: Feedforward versus feedback modulation of human vestibular-evoked balance responses by visual self-motion information.
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 approximately 400 ms), 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.
authors: MRC Human Movement Group, Sobell Department for Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London WC1N 3BG, UK. b.day@ion.ucl.ac.uk
authors: Brian L
authors: BL
authors: Day
authors: Michel
authors: M
authors: Guerraz
mesh_terms: D000328:Adult; D003463:Cues; D004558:Electric Stimulation; D005133:Eye Movements; D025461:Feedback, Physiological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009039:Motion Perception; D010775:Photic Stimulation; D004856:Postural Balance / Q000502:physiology*; D011597:Psychomotor Performance; D011930:Reaction Time; D014722:Vestibule, Labyrinth / Q000502:physiology*; D014796:Visual Perception