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Jocelyn Faubert, Rémy Allard, Jean-Marie Hanssens; Effect of visual sway on postural balance in a full immersive environment. Journal of Vision 2005;5(8):320. doi: 10.1167/5.8.320.
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The role of visual input on postural balance remains relatively unknown. As the population ages, it becomes important to determine possible effects of visual distortion induced from ophthalmic lenses used to correct presbyopia on the capacity to interact with the environment. One of the consequences of progressive ophthalmic lenses used for presbyopia correction is induced sway. i.e. the world appears to move up and down in peripheral vision under certain viewing conditions. A full immersive environment is ideal to answer such questions as the virtual world is not limited to screen size and we can therefore measure the full impact of sway on the ability to keep our balance. We used a CAVE composed of four projection surfaces (3 walls and the floor) equipped with a motion tracking system (Flock of Birds) to determine the effect of a variety of speeds and amplitudes of sway movement on posture. Sensors were positioned at the head and lower back and recordings were made while the subjects were observing visual stimuli. Three amplitudes (1, 2 & 4 deg max slope) and 10 speeds (from 0.03 to 2 Hz) were evaluated. The virtual image was a checkerboard pattern composed of 0.25x0.25m squares on a 10x10m floor size. The subjects were asked to remove their shoes and stand looking straight ahead with both feet together and side-by-side. Five young healthy observers participated in the study. The results show a clear effect of visual sway on posture particularly at lower temporal frequencies. Amplitude effects were only evident at the lowest temporal frequency. The amplitude of displacement responses show a low-pass tuning function as a function of speed. Phase delays are also clearly evident for the 5 lower temporal frequencies but appear to break down with higher speeds. In conclusion, we show that visual input is extremely important for maintaining postural balance, particularly under low speed conditions. Further work, will evaluate the effect of sway on older observers.
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