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Optimal feedback control as a theory of motor coordination

Abstract

A central problem in motor control is understanding how the many biomechanical degrees of freedom are coordinated to achieve a common goal. An especially puzzling aspect of coordination is that behavioral goals are achieved reliably and repeatedly with movements rarely reproducible in their detail. Existing theoretical frameworks emphasize either goal achievement or the richness of motor variability, but fail to reconcile the two. Here we propose an alternative theory based on stochastic optimal feedback control. We show that the optimal strategy in the face of uncertainty is to allow variability in redundant (task-irrelevant) dimensions. This strategy does not enforce a desired trajectory, but uses feedback more intelligently, correcting only those deviations that interfere with task goals. From this framework, task-constrained variability, goal-directed corrections, motor synergies, controlled parameters, simplifying rules and discrete coordination modes emerge naturally. We present experimental results from a range of motor tasks to support this theory.

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Figure 1: Redundancy exploitation.
Figure 2: Final state variability.
Figure 3: Trajectory variability.
Figure 4: Hitting and throwing.
Figure 5: Hand manipulation.
Figure 6: Telescopic 'arm' model.

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Acknowledgements

We thank P. Dayan, Z. Ghahramani, G. Hinton and G. Loeb for discussions and comments on the manuscript. E.T. was supported by the Howard Hughes Medical Institute, the Gatsby Charitable Foundation and the Alfred Mann Institute for Biomedical Engineering. M.I.J. was supported by ONR/MURI grant N00014-01-1-0890.

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Correspondence to Emanuel Todorov.

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Todorov, E., Jordan, M. Optimal feedback control as a theory of motor coordination. Nat Neurosci 5, 1226–1235 (2002). https://doi.org/10.1038/nn963

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