Role of Visual Feedback in Upright Posture Control

We studied the role of visual feedback in upright posture control on the sagittal plane. In posture control, each sensory system has the following roles: initial detection of sway, suppression of short-term sway around the equilibrium point, and suppression of longterm sway induced by a slow shift in equilibrium. Experiments were conducted to examine features of each sensor and then visual contribution was studied. Based on measured sensory thresholds for the perception of sway during standing, it was suggested that visual input provided sensitive means of perceiving postural sway. Body sway of a subject was measured under several conditions in which the subject controlled upright posture utilizing the definite number of sensors. By analyzing and comparing measured sway waveforms under each condition, it was clear that the visual system suppressed short-term sway. Spectral analysis showed that the visual system suppressed body sway in a low frequency range around 0.2 Hz. Though visual feedback contains a large time delay, the influence of the delay is small in the low frequency range. It is rational that vision is efficient at suppressing body sway in the low frequency range.