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Guillaume L. Giraudet, Brigitte Millette, Sharlee Deziel-Gagnon, Jocelyn Faubert; Effect of Transient Visual Changes on Postural Control. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4826.
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The aim of the current study was to determine the effect on postural stability of various transient changes in the visual environment following different adaptation periods.
Thirty-four subjects participated in the experiment. They stood in a fully immersive virtual reality environment. The stimulus was a 3D textured tunnel, either static or moving sinusoidaly at a frequency of 0.5Hz in the anterior-posterior direction. Each trial was composed of 3 stages. The first one was called "Baseline" (10s), during which the tunnel was static. Then the stimulus started oscillating back and forth for 10, 20 or 30 seconds; the "Adaptation" stage. Three "post-adaptation" conditions were then considered: i) no visual information; ii) static tunnel; iii) phase inversion of the moving pattern. A magnetic motion sensor, located on the stereoscopic goggles, was used to register body movements. Postural reactions to the various visual conditions were described by the Body Sway Amplitude (BSA), that is the postural sways at the frequency of the oscillating tunnel, so the tendency of the subject to follow the moving scene.
Comparing Baseline and Adaptation stages, results showed that there was a significant increase in the amplitude of sways due to the onset of the moving stimulus. Then, when the tunnel disappeared or stopped, BSA decreased significantly. The phase inversion had no measurable effect on BSA. The same pattern of results was found for all Adaptation stage durations.
The results confirm the major impact of the moving stimulus on postural control. As soon as the tunnel starts moving, subjects tend to follow its displacement. This adaptation is fast, less than 10 seconds, as the three Adaptation sequences used showed no differences.
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