Analysis of role of vision in human upright posture control

We investigated the role of visual feedback in human upright posture control. To make the role of vision clear, we compared the visual, vestibular and somatosensory feedback systems in their ability to perceive movement and suppress short- and long-term sway. First, we measured thresholds for the perception of movement Then effects of each feedback system to suppress short- and long-term sway were analyzed through posture control experiments, in which the available sensory input was limited. The visual and somatosensory thresholds were small (<0.1 degree) while the vestibular threshold was relatively large (>0.5 degree). The results of the posture control experiments suggested that the visual system contributed to suppression of sway in the frequency range below 0.4 Hz and the system had a minor effect in frequencies above 0.5 Hz. These results support our previous finding that the visual system does not allow a normal subject to maintain an upright posture by itself. The somatosensory system, on the other hand, suppressed body sway around 0.2 and 0.9 Hz. The higher frequency range might enable the system to maintain an upright posture by itself.