Effect of Moving Tactile Stimuli to Sole on Body Sway in Quiet Stance

This study examined whether moving tactile stimuli to the soles induce body sway in a quiet stance. Fifteen healthy participants maintained a quiet stance. Tactile stimuli moving along the anterior-posterior (AP) or medio-lateral (ML) axis were provided to the soles of the feet. The center of pressure (COP) along the ML axis was dependent on the phase of the tactile stimuli moving along the ML axis when vision was unavailable. The direction of the body sway was opposite to the stimulus side. They must have perceived the body sway to the stimulated side. Based on this, when humans perceive the body sway along the ML axis, they sway the body to the direction contralateral to the stimulated side to compensate for the perceived body sway. The greater effect of the moving tactile stimuli on phase-dependent body sway, particularly when vision was unavailable, can be explained by the view that body sway in the ML axis, in accordance with the loci of the tactile sensation moving along the same axis, becomes unmasked when vision is absent. The total COP displacement during tactile stimulation moving along the AP axis was larger than that without stimulation, particularly when vision was unavailable. This can be explained by the view that, through intermodal reweighting, the contribution of tactile sensation to controlling body sway along the AP axis increases to compensate for the lack of visual input regulating COP displacement in this axis.