VIRTUAL TIME-TO-COLLISION AND HUMAN POSTURAL CONTROL

This article is a report on 3 experiments designed so that the role of virtual time-to-collision (VTC), which specifies the spatiotemporal p roximity of the center of pressure to the postural stability boundary in the regulation of posture in upright stances, could be examined. Vi rtual time-to-collision was estimated for normal upright stance with d ifferent bases of support, and far postural oscillations in which the speed of movement and instructional constraints on the coordination mo de used were manipulated. The results showed that virtual time-to-coll ision was predictably reduced as (a) the base of support was reduced, (b) the speed of the postural oscillation was increased, and (c) the n umber of biomechanical degrees of freedom regulated in the coordinatio n mode increased. Over a range of task conditions, the coefficients of variation of the VTC time-series were significantly lower than the co efficients of variation for the velocity and acceleration time-series of the center of pressure. The absolute values of VTC increased with t he increment of the ground reaction forces a performer generated to av oid falling while approaching the stability boundary. These findings a re consistent with the proposition that VTC may serve as an organizing informational control parameter for posture.