MOTION PARALLAX IS USED TO CONTROL POSTURAL SWAY DURING WALKING

Three experiments tested the hypothesis that postural sway during loco motion is visually regulated by motion parallax as well as optical exp ansion. Oscillating displays of three-dimensional scenes were presente d to participants walking on a treadmill, while postural sway was reco rded. Displays simulated: (a) a cloud, in which parallax and expansion are congruent, (b) a hallway, (c) the side walls of the hallway, (d) a ground surface, (e) a wall, (f) the wall with a central hole, (g) a hall farther from the observer, and (h) a wall farther from the observ er. In contrast to previous results with a hallway, responses with the cloud were isotropic and directionally specific. The other displays d emonstrated that motion parallax was more effective than simple horizo ntal flow in eliciting lateral sway. These results are consistent with the hypothesis that adaptive control of sway during walking is based on congruent expansion and parallax in natural environments.