Influence of optic flow stimuli on postural response. II. Stabilometry

Introduction Several researches have been aimed at studying the balance control looking at the variation of the center of pressure (COP) trajectory induced by variation of the visual field (Collins & De Luca, 1995; Accornero, 1997). Indeed, presence of a visual stimulus produce less sway speed than the dark (Lee & Lishman, 1975). However, little is known about the modulation of optic flow stimuli on the body sway. Aim of this study was to verify how the direction of optic flow can affect the COP parameters like speed, trace length, equivalent area and equivalent radius. Methods Stabilometric data were recorded in 24 healthy right-handed volunteers (12 M and 12 F, mean age 24.5±2.9) who standed on two Kirstel force platforms. Experiments were performed in the dark. Stimuli were presented on a wide screen, placed 115 cm from the subjects’ eyes, covering 135 x 107° of visual field. Stimuli were two full screen optic flow, expansion and contraction, and random dots motion as control stimulus. Postural responses data were acquired by the SMART BTS® at 1000 Hz (BTS® Bioengineering Inc.). Data acquisition included 5 trials per stimulus for about 30-s each. Results We performed a repeated measure ANOVA on the 24 subjects for each COP parameter. Speed: we found significant differences across the optic flow stimuli (p=0.042) and significant interaction between stimulus and sex (p=0.009). Trace length: results showed significant interaction between stimulus and sex (p=0.001). Equivalent area: we found significant interaction between stimulus and sex (p