Abstract
The present study investigated the role of visual feedback in upright posture control in 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, and suppression of long-term sway induced by slow shift of the equilibrium. Experiments were performed to examine characteristics of each sensor and then visual contribution was studied. On the basis of measured sensory thresholds for the perception of sway during standing, it was suggested that visual inputs provided sensitive means of perceiving postural sway. Under several conditions in which a subject controlled his upright posture utilizing the definite number of sensors, subject's body sway was measured. By analysis and comparison of measured sway waveforms under each condition, it was clear that the visual system suppressed short-term sway. Spectral analysis provided the result that the visual system suppressed body sway in the low frequency range around 0.2Hz. Though the visual feedback system contains a large time delay, influences of the delay are small in the low frequency range. It is rational that the visual system is efficient to suppress body sway in the low frequency range.
