Grip force adjustments induced by predictable load perturbations during a manipulative task |
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Authors: | D J Serrien P Kaluzny U Wicki M Wiesendanger |
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Institution: | (1) Laboratory of Motor Systems, Department of Neurology, University of Berne, Inselspital, BHH M129, CH-3010 Berne, Switzerland, CH |
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Abstract: | The experiment examined the anticipatory modulation of grip force with respect to load force during a drawer opening task.
An impact force was introduced by a mechanical stop that arrested movement of the pulling hand. The results showed a typical
grip force profile which consisted of two evolving phases, one to control drawer movement onset, and the other to secure grip
force at the expected impact. Initially, grip force increased with the load force that was developed to overcome the inertia
of the drawer. After the first peak, a small decline was observed, followed by a proactive grip force increase prior to the
time of impact. During this ramp-like increase of grip force, load force remained unchanged. In addition, a reactive response
was triggered by the impact. That anticipatory control with respect to an impact force is not innate but, rather, is learned
by experience was evidenced by a comparison of adults and children. Whereas adults made the characteristic grip force adjustments
to anticipate the impact, children used a probing strategy with irregular build-up of force until impact. Furthermore, adults
calibrated the second phase of the grip force profile in the initial trials of the task, indicating that grip force was rapidly
updated with information related to the impact force. The present results demonstrate that grip-load force coordination during
manipulation is a necessity for dealing with destabilizing load perturbations produced by self-induced movement and impact
forces. It is concluded that grip force is adjusted automatically, but in a flexible manner, to secure grip in accordance
with the characteristics of the pulling synergy.
Received: 13 October 1997 / Accepted: 29 June 1998 |
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Keywords: | Grip force Load force Load perturbations Anticipation Development |
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