Reaching goals and representing space: different implications for stability and variability of behavior

Sandro Mussa-Ivaldi
Depts. of Physiology, Physical Medicine & Rehabilitation and Biomedical Engineering, Northwestern University

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     Last modified: April 28, 2007
     Presentation date: 08/11/2007 8:40 AM in MCC
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Abstract
Recent theoretical [2] [3] and experimental [1] studies have suggested that in order to insure stable behavior of a controlled endpoint, the motor system may exploit the possibility to redirect the variability of movements over subspaces defined by redundant degrees of freedom that do not have an effect on the potion of the controlled endpoint. According to the framework of Todorov and Jordan [3], an optimal controller is only concerned with the final goal of a movement and the shape of trajectories follows as a side-effect. Here I will present experimental results and theoretical considerations that go in a different direction, suggesting that the stability of trajectories and their spatiotemporal shapes leads to a stable representation of motor space and of its metric properties. In particular, the ability of the motor system to form consistent and repeatable behaviors requires the formation and the explicit control of degrees of freedom that are not contributing to the motion of the controlled endpoint.


References
[1] Latash ML, Scholz JP, and Schoner G. Motor control strategies revealed in the structure of motor variability. Exercise and sport sciences reviews 30: 26-31, 2002.
[2] Scholz JP and Schoner G. The uncontrolled manifold concept: identifying control variables for a functional task. Experimental Brain Research 126: 289-306, 1999.
[3] Todorov E and Jordan MI. Optimal feedback control as a theory of motor coordination. Nature Neuroscience 5: 1226-1235, 2002.