Non-linear stimulus-response behavior of the human stance control system is predicted by optimization of a system with sensory and motor noise |
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Authors: | Herman van der Kooij Robert J Peterka |
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Institution: | (1) Department of Biomechanical Engineering, University of Twente, 7500 AE Enschede, The Netherlands;(2) Department of Biomechanical Engineering, Delft University of Technology, Delft, The Netherlands;(3) Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR, USA |
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Abstract: | We developed a theory of human stance control that predicted (1) how subjects re-weight their utilization of proprioceptive
and graviceptive orientation information in experiments where eyes closed stance was perturbed by surface-tilt stimuli with
different amplitudes, (2) the experimentally observed increase in body sway variability (i.e. the “remnant” body sway that
could not be attributed to the stimulus) with increasing surface-tilt amplitude, (3) neural controller feedback gains that
determine the amount of corrective torque generated in relation to sensory cues signaling body orientation, and (4) the magnitude
and structure of spontaneous body sway. Responses to surface-tilt perturbations with different amplitudes were interpreted
using a feedback control model to determine control parameters and changes in these parameters with stimulus amplitude. Different
combinations of internal sensory and/or motor noise sources were added to the model to identify the properties of noise sources
that were able to account for the experimental remnant sway characteristics. Various behavioral criteria were investigated
to determine if optimization of these criteria could predict the identified model parameters and amplitude-dependent parameter
changes. Robust findings were that remnant sway characteristics were best predicted by models that included both sensory and
motor noise, the graviceptive noise magnitude was about ten times larger than the proprioceptive noise, and noise sources
with signal-dependent properties provided better explanations of remnant sway. Overall results indicate that humans dynamically
weight sensory system contributions to stance control and tune their corrective responses to minimize the energetic effects
of sensory noise and external stimuli. |
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Keywords: | |
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