Virtual scene velocity influences postural responses to an inclined base of support

Orientation of the body has been shown to adapt to sustained stance on a tilted support surface in subjects who were blindfolded or who had their eyes closed. Postural adaptation occurs even when the lower limbs are constrained, suggesting that there is central adaptation of the perception of vertical. These studies, however, were performed in the absence of visual inputs and it is not clear whether the presence of visual inputs would alter a central adaptive response to a physical displacement in space. In this study we have explored the relative contributions of surface tilt and visual velocity on the initial process of realignment to the vertical. Pitch motion of the visual field was presented at varying velocities to eight subjects (29.9 plusmn 2.8 yrs) standing quietly on a 3 deg toes-up tilt of the base of support. Onset of virtual scene and platform movement were synchronized in all trials. We hypothesized that motion of the visual world would affect the ability to return to the initial vertical position while standing on a tilted base of support. We found that in the first few seconds following stance on a tilted base of support, orientation in space was greatly influenced by the velocity of visual scene motion.