Influences on Postural Orientation in a Virtual Environment

The purpose of this study was to determine how visual context affects intersegmental coordination during a postural stabilization task in older adults who are healthy or who have bilateral labyrinthine deficiency. Six healthy elderly (60-78 yrs) and 3 labyrinthine deficient (59-86 yrs) adults stood on a platform translating sinusoidally (plusmn10 cm at 0.25 Hz) in the a-p direction within an immersive, wide field of view virtual environment (scene) moving fore-aft (plusmn6.1 m at 0.1 Hz or plusmn2.4 m at 0.25 Hz). Kinematics of the head, trunk, and shank were collected with a 6 camera motion analysis system. Relative angles between segments were calculated and intersegmental phases and RMS values computed. Power was derived from fast Fourier transforms (FFT). Intersegmental motion varied as the visual scene was varied in magnitude, direction, and frequency from that of the support surface, suggesting that specific parameters of visual motion had a direct effect on the metrics of the postural response. When the visual parameters had little in common with the support surface disturbance, the preferred postural strategy was to approximate the body as an inverted pendulum with the ankle as the pivot point. These data imply that a conflict between visual and proprioceptive feedback will alter the metrics of the postural response and that the specific visual context is an important component of the motor plan calculations for the organization of the postural response.