Abstract
We have examined the interaction among individual finger forces in tasks that required the production of the total force by a subset of fingers in a particular direction in the flexion–extension plane. Nine subjects produced fingertip forces in a prescribed direction with a maximum voluntary contraction (MVC) effort and held the peak force for two seconds. Six finger combinations were tested, four single-finger tasks—Index (I), Middle (M), Ring (R) and Little (L)—one two-digit task (IM), and one four-digit task (IMRL). The subjects were asked to generate the finger forces in two directions, 0° (perpendicular to the surface of the transducer) and 15° toward the palm. In all task conditions, there were two experimental sessions, with and without visual feedback on the task force vector. The main findings were:
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1.
The target direction significantly affected the constant error (CE) but not the variable error (VE) while removal of the feedback resulted in an increase in VE.
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2.
The direction of the forces produced by fingers that were not explicitly required to produce force (enslaved fingers) depended on the target direction.
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3.
In multi-finger tasks, the individual fingers produced force in directions that could differ significantly from the target direction, while the resultant force pointed in the target direction.
There was a negative co-variation among the deviations of the directions of the individual finger forces from the target direction. If a finger force vector deviated from the target, another finger force vector was likely to deviate in the opposite direction. We conclude that a multi-finger synergy is involved in the control of the finger force direction.
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Acknowledgments
Preparation of this paper was supported in part by NIH grants AR-048563, AG-018751, and NS-35032. The authors are grateful to Zbigniew Waskiewicz for his help in conducting the experiments and to Michelle L. Olson for her help in proofreading the manuscript.
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Gao, F., Latash, M.L. & Zatsiorsky, V.M. Control of finger force direction in the flexion-extension plane. Exp Brain Res 161, 307–315 (2005). https://doi.org/10.1007/s00221-004-2074-z
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DOI: https://doi.org/10.1007/s00221-004-2074-z