A gentle introduction to the dynamic set-point model of human postural control during perturbed stance

Three models of increasing complexity to capture three observed phenomena of postural control are described. The first-order model mimics the increase in standard deviation of sway with eyes closed, but none of the other phenomena. The damped spring model captures both the increase in standard deviation of sway with eyes closed and the change from phase-lag to phase-lead with increasing frequency of oscillation of a visual surround. The final model, the dynamic set-point model, extends the damped spring model by a degree of freedom that reflects the observed slow drift in baseline. Under the assumption of a strong coupling to positional information, the dynamic set-point model predicts a dependence between natural frequency and position coupling constant of the damped spring model. It is shown that this prediction is borne out in data obtained from haptically perturbed stance but not in data obtained from visually perturbed stance. (C) 2000 Published by Elsevier Science B.V. All rights reserved.