Stability of Hand Force Production: II. Ascending and Descending Synergies

Stability of Hand Force Production: II. Ascending and Descending Synergies We combined the theory of neural control of movement with referent coordinates and the uncontrolled manifold hypothesis to investigate multi-finger coordination. We tested hypotheses related to stabilization of performance by co-varying control variables, translated into apparent stiffness and referent coordinate, at different levels of an assumed hierarchy of control. Subjects produced an accurate combination of total force and total moment of force with the four fingers under visual feedback on both variables and after feedback was partly or completely removed. The "inverse piano" device was used to estimate control variables. We observed strong synergies in the space of hypothetical control variables which stabilized total force and moment of force, as well as weaker synergies stabilizing individual finger forces; while the former were attenuated by alteration of visual feedback, the latter were much less affected. In addition, we investigated the organization of "ascending synergies" stabilizing task-level control variables by co-varied adjustments of finger-level control variables. We observed inter-trial co-variation of individual fingers' referent coordinates stabilizing hand-level referent coordinate, but observed no such co-variation for apparent stiffness. The observations suggest the existence of both descending and ascending synergies in a hierarchical control system. They confirm a trade-off between synergies at different levels of control and corroborate the hypothesis on specialization of different fingers for the control of force and moment. The results provide strong evidence for the importance of central back-coupling loops in ensuring stability of action. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Neurophysiology The American Physiological Society

Stability of Hand Force Production: II. Ascending and Descending Synergies

Journal of Neurophysiology Jan 18, 2018

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ISSN
0022-3077
eISSN
1522-1598
D.O.I.
10.1152/jn.00045.2018
Publisher site
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Abstract

We combined the theory of neural control of movement with referent coordinates and the uncontrolled manifold hypothesis to investigate multi-finger coordination. We tested hypotheses related to stabilization of performance by co-varying control variables, translated into apparent stiffness and referent coordinate, at different levels of an assumed hierarchy of control. Subjects produced an accurate combination of total force and total moment of force with the four fingers under visual feedback on both variables and after feedback was partly or completely removed. The "inverse piano" device was used to estimate control variables. We observed strong synergies in the space of hypothetical control variables which stabilized total force and moment of force, as well as weaker synergies stabilizing individual finger forces; while the former were attenuated by alteration of visual feedback, the latter were much less affected. In addition, we investigated the organization of "ascending synergies" stabilizing task-level control variables by co-varied adjustments of finger-level control variables. We observed inter-trial co-variation of individual fingers' referent coordinates stabilizing hand-level referent coordinate, but observed no such co-variation for apparent stiffness. The observations suggest the existence of both descending and ascending synergies in a hierarchical control system. They confirm a trade-off between synergies at different levels of control and corroborate the hypothesis on specialization of different fingers for the control of force and moment. The results provide strong evidence for the importance of central back-coupling loops in ensuring stability of action.

Journal

Journal of NeurophysiologyThe American Physiological Society

Published: Jan 18, 2018

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