Effects of standardized optokinetic stimuli on standing stability

BACKGROUND: Human standing stability is ensured by means of a sensory-motor control system. Proprioceptivity is most important among sensory afferences. At this time, less is known about the effect of standardized visual stimuli on motor programs towards support of body stability. These investigations were performed with special consideration for different strains on bunions and heels of both feet. METHODS: 42 healthy individuals (averaged age 29.6 years) were investigated with relaxed standing on the static force platform of Portable Multiplate System P. M. S. with optokinetic stimuli in horizontal, vertical and torsional direction (speed 80 degrees/s). Conducted by computer-analysis, the stability index, varying foot-pressure on heels and bunions, Fourier spectral analysis, and weight distribution index were counted. The eye movements were controlled with help of the PENG device. RESULTS: The optokinetic stimulations led to partial statistically significant impairments of stability particularly with torsional stimuli, yet notably improved stability with left stripes pattern. The sensory conflict between visual and other sensory inputs led to a statistically significant shift of sway frequencies to the higher ranges. On stimulation, the distribution of pressure to the feet changed. The preponderance to rest on the left side was equalized. The heels were considerably strained more with visual stimuli in all directions. Individuals felt more agreeable, toward stripes vertically directed while torsionally directed stripes elicited particular strain. CONCLUSION: Sensory conflicts between visual and other sensory inputs for maintaining the upright body position were found to impair the stability. Nevertheless these conflicts were partially compensated by motor programs more straining to the heels.