SPATIAL-FREQUENCY-RELATED EFFICACY OF VISUAL STABILIZATION OF POSTURE

The present study investigates the efficacy of visual stabilisation of posture for different spatial frequencies of a visual stimulus. Circu lar sine wave gratings were used to analyse the correlation between pe rception of motion in depth and stabilisation of fore-aft sway by the mechanism of detecting changes in target size. Body sway was recorded by a force-measuring platform (series A) and, in addition, by simultan eous tracking of infrared markers fixed to the subject's body (series B). Mean velocity and amplitude (RMS) of body sway were calculated in both sagittal (a-p) and lateral (l-r) planes. Sagittal sway was of lea st magnitude when viewing contrast gratings with lowest thresholds, wh ereas higher thresholds resulted in increasing sway parameters. As int ended by the design of the stimuli, sagittal sway was correlated close r with the stabilising effect exerted by the different stimuli than wa s lateral sway. Sway velocity was reduced more efficiently, however, w ith a lower correlation with the psychophysical transfer function, tha n was RMS sway. Since sway velocity measured by the platform is sugges ted to depend to a greter extent on dynamic muscle forces generated at each individual body site the results indicate that visual informatio n can be used to reduce and thereby optimise dynamic muscle action (sw ay velocity) even though static body sway is either not or less reduce d. A comparable economisation of sway velocity but not of RMS sway was also seen at the end of posture investigations, indicative of positiv e training effects.