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<0.001). Equivalent radius: results showed significant interaction between stimulus and sex (p=0.002). These results indicate that the direction of optic flow stimuli strongly modifies the upright posture. Male and female populations are differently affected by the optic flow direction. Discussion These experiments confirmed that the optic flow input modulates the neural control of body sway. Because the sensitivity to the body sway is greatly dependent on the visual feedback, results of this research may allow to lead rehabilitation programs in patients with visual deficits responsible of postural modification. Furthermore, the described changes in the sway parameters due to the optic flow stimulus direction could allow to develop specific sport visual training. References Accornero N, Capozza M, Rinalduzzi S, Manfredi GW (1997) Electroencephalogr Clin Neurophysiol 105:213-219. Collins JJ & De Luca CJ (1995) Exp Brain Res 103:151-163. Lee D & Lishman JR (1975) Journal of Human Movement Studies 1:87-95.