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Jean-Marie Hanssens, Guillaume Giraudet, Remy Allard, Jocelyn Faubert; Modulating Somatosensory Input Makes People More Visually Dependant For Postural Control. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3014.
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Elders are well known to be more dependent on vision to control their posture. However, as vision is also decreasing with age, the increase of vision weight in postural control may be problematic. The purpose of the present study was to modulate the somatosensory input on young subjects to determine whether the alteration of these inputs could explain the increase of visual dependence for postural control.
Twelve young observers (22 to 35 years of age) were placed in a Full Immersive Virtual Environment where the virtual floor, defined by a 10 x 10 m black and white checkerboard pattern, oscillated sinusoidally. The slope (1, 2 and 4°) and temporal frequency (0.03 to 2.0 Hz) of the oscillations were systematically manipulated. The virtual floor moved from right to left (medial-lateral ML) and from front to back (anterior-posterior AP). Somatosensory inputs were modulated with a T-foam cushion placed under the feet (Cornilleau-Peres, 2005). The Body Sway Amplitude (BSA) and Velocity Root Mean Square (VRMS) were extracted from the electromagnetic tracker positioned on the head and transformed using Fourier analysis.
Results showed a significant increase of postural reactivity when modulating somatosensory inputs in young subjects. Stoffregen et al. showed, in 1999, that postural control was more visual dependant for AP stimulation. However, our results showed that ML postural control became more visually-dependant when the somatosensory feedbacks were affected.
The increase of visual dependence for postural control is related to the alteration of somatosensory feedback for young subjects and may explain the age related visual dependency. Perturbing somatosensory inputs with a foam cushion increases the visually induced postural reactivity for ML stimulation. ML postural control seems to be more related to somatosensory inputs whereas AP postural control seems to be more related to vision inputs.
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