Visual control in the upright standing position

The role of static and kinetic visual information in the regulation of the upright standing position was studied in 7 healthy subjects.The subject stood on a stabilometer with the feet close together and gazed at the visual pattern (11 vertical stripes drawn at intervals of 4 cm). The postural sway under normal illumination, stroboscopic illumination at a frequency of 10 Hz, 5 Hz, and 1.4 Hz, and in darkness was recorded for 30 seconds with an X-Y recorder and stored in the disk of a microcomputer. On the basis of the stored data, concerning the area, unit locus length, forward-backward and right-left diameters, standard deviation, skewness and kurtosis of amplitude, the probability density distribution and power spectrum were calculated by a specially designed program.1. The size of body sway under stroboscopic illumination at a frequency of 1.4 Hz was larger than in the dark. Examinations related to sway-area, for-ward-backward and right-left diameters, and standard deviation of amplitude probability density distribution showed similar results.2. Kurtosis tended to be small under stroboscopic illumination at a frequency of 1.4 Hz.3. The rate of low frequency (0.033-0.195 Hz) in the power spectra of body sway under stroboscopic illumination at a frequency of 1.4 Hz was larger than in the dark.Static visual information without kinetic visual information caused destabilization of posture regulation. Kinetic visual information plays a major role in visual control in the upright standing position, especially in the control of body sway at low frequency.