Article

Sudden addition or removal of visual information can be particularly critical to
balance control. The promptness of adaptation of stance control mechanisms is
quantified by the latency at which body oscillation and postural muscle activity
vary after a shift in visual condition. In the present study, volunteers stood on
a force platform with feet parallel or in tandem. Shifts in visual condition were
produced by electronic spectacles. Ground reaction force (center of foot
pressure, CoP) and EMG of leg postural muscles were acquired, and latency of CoP
and EMG changes estimated by t-tests on the averaged traces. Time-to-reach
steady-state was estimated by means of an exponential model. On allowing or
occluding vision, decrements and increments in CoP position and oscillation
occurred within about 2s. These were preceded by changes in muscle activity,
regardless of visual-shift direction, foot position or front or rear leg in
tandem. These time intervals were longer than simple reaction-time responses. The
time course of recovery to steady-state was about 3s, shorter for oscillation
than position. The capacity of modifying balance control at very short intervals
both during quiet standing and under more critical balance conditions speaks in
favor of a necessary coupling between vision, postural reference, and postural
muscle activity, and of the swiftness of this sensory reweighing process.
CI - Copyright (c) 2010 Elsevier B.V. All rights reserved.

Langue : ANGLAIS