Quantitative analysis of human walking trajectory on a circular path in darkness.

Thirteen normal (eight young and five older) subjects and a patient who was removed left sided acoustic neurinoma were tested to walk blindfolded along circular paths. They were asked to walk completing two revolutions and to stop when they judged they had returned to the initial position with their head faced to the initial directions. Movements of two markers on the subjects head were recorded by three dimensional motion analyzing system (ELITE system) at 50 Hz which allowed us to measure (a) total walked distance, (b) average radius of the trajectory, and (c) cumulative angle of rotation. Eight young subjects were tested on three circles with radii 0.5, 0.9, and 1.15 m, in two conditions (control, and with mental arythmetic), only to clockwise direction. Five older subjects and a patient were tested on a circle of 0.9 m radius in two conditions, but to both directions, counterclockwise and clockwise. Walked trajectories of young subjects were smooth, whereas those of older subjects tended to be polygonal. Young subjects overshot the ideal distance (6.6%) and ideal radius (9.5%), whereas they undershot the ideal angle (5.1%). There was no effect of circle size or condition on these variables. On the other hand, there was a significant effect of condition on average radius in the older group. The performance of older subjects seemed to be affected by the concurrent mental task. Comparing the counterclockwise walk, the older subjects undershot the turning angle much more than the young subjects which suggest deficits in the vestibular function with aging. The patient showed larger radius and smaller angle while she turned to the healthy side (clockwise) than to the affected side (counterclockwise). Lack of unilateral vestibular information seemed to have affected the circular walking trajectory.