Body sway adaptation to addition, but not withdrawal of stabilizing visual information is delayed by a concurrent cognitive task

Aim of this study was to test the effects of a concurrent cognitive task on the promptness of the sensorimotor integration and reweighting processes following addition and withdrawal of vision. Fourteen subjects stood in tandem while vision was passively added and removed. Subjects performed a cognitive task, consisting of counting backwards in steps of three, or were 'mentally idle'. We estimated the time interval, following addition and following withdrawal of vision, at which body sway began to change. We also estimated the time constant of the exponential change in body oscillation until the new level of sway was reached, consistent with the current visual state. Under the mentally-idle condition, mean latency was 0.67 s and 0.46 s, and mean time constant was 1.27 s and 0.59 s, for vision addition and withdrawal, respectively. Following addition of vision, counting backward delayed the latency by about 300 ms, without affecting the time constant. Following withdrawal, counting-backward had no significant effect on either latency or time-constant. The extension by counting backwards of the time-interval to stabilization onset on addition of vision suggests a competition for cortical resources allocation. Conversely, the absence of cognitive-task effect on the rapid onset of destabilization on vision withdrawal, and on the relevant reweighting time-course, advocates the intervention of a subcortical process. Diverting attention from a challenging standing task discloses a cortical supervision on the process of sensorimotor integration of new balance-stabilizing information. A subcortical process would instead organize the response to removal of the stabilizing sensory input.

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