Perceptions of orientation after vestibular, visual and proprioceptive conditioning
Multiple Paper Presentation

Rebecca St George
Prince of Wales Medical Research Institute

Richard Fitzpatrick
Prince of Wales Medical Research Institute

     Abstract ID Number: 120
     Last modified: June 5, 2007
     Presentation date: 07/07/2007 2:00 PM in Quad General Lecture Theatre
     (View Schedule)

Abstract
Background:
Proprioceptive, visual, and vestibular systems provide the information used to control balance and orientation. Conditioning proprioceptive inputs by walking on a rotating turntable causes subjects, afterwards, to walk in a direction counter to the platform without perceiving their altered trajectory. Our aims here are to determine whether conditioning visual and vestibular sensory channels elicits similar responses and to determine how the three channels are fused to create a coherent internal model.
Methods:
A rotating platform, a rotating projected visual field, and galvanic vestibular stimulation (GVS) with precise head orientation were used to rotate the proprioceptive, visual, and vestibular inputs respectively about the same vertical axis. Each test on ten subjects comprised a conditioning phase, in which afferent channels were stimulated while the subject stepped in place with eyes open, followed by a response phase, in which the stimuli stopped and subjects, blindfolded, continued stepping while attempting to maintain constant whole-body orientation. Conditioning was tested for varying durations and intensities: visual for 30,60,180,360s at 10,20,40 °s-1), vestibular for 60,180,360s at GVS of ±1.8mA.

Results:
Following visual field motion all subjects turned in the direction of the conditioning stimulus. This effect was most pronounced in the first 20s and decayed over several minutes. The post GVS response was toward the direction of the cathode, peaked after 60s and the peak rate increased with exposure time. When conditioning stimuli were paired in the same direction the response trajectory reflected the time course of the individual responses. However when conditioned in opposing directions the trajectory was a compromise between the two and was variable between subjects.

Conclusions:
An internal model of body orientation is updated online by visual, vestibular and proprioceptive stimuli. The three sensory channels have different time constants and resolution. The availability of each channel alters the reliance placed the others.

To be Presented at the Following Symposium:
Multisensory mechanisms of posture control
Other papers in this Symposium:

• Brian Day
  MRC Human Movement Group, Sobell Department for Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, London
  Michel Guerraz
  Laboratoire de Psychologie et Neurocognition CNRS UMR 5105 Université de Savoie, France.
  Feedforward versus feedback modulation of human vestibular-evoked balance responses by visual self-motion information
• Stephen Lord
  Prince of Wales Medical Research Institute
  Annie Butler
  Richard Fitzpatrick
  PROPRIOCEPTION, STRENGTH AND STANDING
• Richard Fitzpatrick
  Prince of Wales Medical Research Institute
  Daina Sturnieks
  Prince of Wales Medical Research Institute
  Rebecca St George
  Prince of Wales Medical Research Institute
  Daniel Wardman
  Vestibular-visual interactions in balance and orientation
• Ian Curthoys
  Psychology, University of Sydney
  Hamish MacDougall
  Psychology, University of Sydney
  Dena Attalla
  Psychology, University of Sydney
  Fabienne MBongo
  LNRS, Universite Paris
  Pierre-Paul Vidal
  LNRS, Universite Paris
  Catherine de Waele
  LNRS, Universite Paris
  Human head and body stability after unilateral vestibular loss