Predictive feedback in human simulated pendulum balancing

Gawthrop, P., Loram, I. and Lakie, M. (2009) Predictive feedback in human simulated pendulum balancing. Biological Cybernetics, 101(2), pp. 131-146. (doi: 10.1007/s00422-009-0325-6)

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In studies of human balance, it is common to fit stimulus-response data by tuning the time-delay and gain parameters of a simple delayed feedback model. Many interpret this fitted model, a simple delayed feedback model, as evidence that predictive processes are not required to explain existing data on standing balance. However, two questions lead us to doubt this approach. First, does fitting a delayed feedback model lead to reliable estimates of the time-delay? Second, can a non-predictive controller provide an explanation compatible with the independently estimated time delay? For methodological and experimental clarity, we study human balancing of a simulated inverted pendulum via joystick and screen. A two-step approach to data analysis is used: firstly a non-parametric model—the closed-loop impulse response—is estimated from the experimental data; second, a parametric model is fitted to the non-parametric impulse-response by adjusting time-delay and controller parameters. To support the second step, a new explicit formula relating controller parameters to closed-loop impulse response is derived. Two classes of controller are investigated within a common state-space context: non-predictive and predictive. It is found that the time-delay estimate arising from the second step is strongly dependent on which controller class is assumed; in particular, the non-predictive control assumption leads to time-delay estimates that are smaller than those arising from the predictive assumption. Moreover, the time-delays estimated using the non-predictive control assumption are not consistent with a lower-bound on the time-delay of the non-parametric model whereas the corresponding predictive result is consistent. Thus while the goodness of fit only marginally favoured predictive over non-predictive control, if we add the additional constraint that the model must reproduce the non-parametric time delay, then the non-predictive control model fails. We conclude (1) the time-delay should be estimated independently of fitting a low order parametric model,(2) that balance of the simulated inverted pendulum could not be explained by the non-predictive control model and (3) that predictive control provided a better explanation than non-predictive control.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Gawthrop, Professor Peter
Authors: Gawthrop, P., Loram, I., and Lakie, M.
College/School:College of Science and Engineering > School of Engineering > Systems Power and Energy
Journal Name:Biological Cybernetics
ISSN (Online):1432-0770
Published Online:09 July 2009

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
476761Intermittent predictive control of man and machineHenrik GolleeEngineering & Physical Sciences Research Council (EPSRC)EP/F069022/1ENG - BIOMEDICAL ENGINEERING