Event Abstract Back to Event Exploiting redundancy for maintaining upright stance – a model of human posture Hendrik Reimann1*, Gregor Schöner1 and John Scholz2 1 Ruhr-Universität Bochum, Institut für Neuroinformatik, Germany 2 University of Delaware, Department of Physical Therapy, United States Models of human quiet stance have to deal with two main problems: estimating the current kinematic state of the body and transforming this estimate into a control signal that prevents the body from falling. Usually the body is interpreted as an inverted pendulum, with most relevant motion at the ankle joint, while the other joints are simply stiffened, reducing the generation of a control signal to a one dimensional problem. Recent experimental data (Hsu et al., J Neurophysiol 97:3024-3035, 2007) have shown that motion at other joints significantly contributes to stabilizing the body during quiet stance. Analysis of the variance in joint space revealed that the movement of multiple joints is organized to minimize deviation of the center of mass (CoM), as indicated by the high variance along the UnControlled Manifold (UCM) of the CoM and low variance in the orthogonal subspace of joint space. Thus it seems that there are aspects of human quiet stance the inverted pendulum approach fails to capture, indicating the need for a model with multiple degrees of freedom. While for an inverted pendulum model falling over is prevented by keeping the body center of mass above the surface of the feet, with more degrees of freedom this is not sufficient, as the body can also ‘fold down’, i.e. buckle at the knees, moving the center of mass straight downward. Also, the effect of gravity is significantly more complicated with multiple degrees of freedom, because the magnitude of the gravitational torque at a given joint depends on the kinematic state of the whole body, not only the current angle of the joint itself. The model we propose treats each joint as a damped mass-spring system, controlled by the CNS via specification of the system’s equilibrium point (λ-model). Using proprioceptive feedback of each joint angle, the equilibrium points are shifted to counteract deviations from a preset value for each joint. This allows to neutralize the destabilizing effects of gravity, without having to estimate it explicitly by an internal model. Although this control scheme manages to keep the body upright, a UCM analysis of the generated angle trajectories reveals a distribution of variance that is quite different from what is observed in human subjects. This is resolved by adding a control mechanism that exploits the redundancy of the task by selectively controlling those directions in joint space that affect the COM position. Keywords: degree of freedom problem, modeling, Posture, redundancy Conference: Bernstein Conference on Computational Neuroscience, Berlin, Germany, 27 Sep - 1 Oct, 2010. Presentation Type: Presentation Topic: Bernstein Conference on Computational Neuroscience Citation: Reimann H, Schöner G and Scholz J (2010). Exploiting redundancy for maintaining upright stance – a model of human posture. Front. Comput. Neurosci. Conference Abstract: Bernstein Conference on Computational Neuroscience. doi: 10.3389/conf.fncom.2010.51.00064 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 16 Sep 2010; Published Online: 23 Sep 2010. * Correspondence: Dr. Hendrik Reimann, Ruhr-Universität Bochum, Institut für Neuroinformatik, Bochum, Germany, hendrikreimann@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Hendrik Reimann Gregor Schöner John Scholz Google Hendrik Reimann Gregor Schöner John Scholz Google Scholar Hendrik Reimann Gregor Schöner John Scholz PubMed Hendrik Reimann Gregor Schöner John Scholz Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.