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Abstract:
Two callosotomy patients and 10 healthy control subjects were
tested on a bimanual force production task. Participants produced
isometric force pulses with both hands simultaneously. Three
different target forces were indicated by bars presented to either
side of fixation. On each trial, the forces for the two hands could
be the same or different. In healthy control subjects three indices
of force-coupling were found: First, the peak-force produced with
one hand was influenced in the direction of the target force of the
opposite hand. Second, trials in which the target forces were the
same showed a smaller variance in produced force than trials in
which the two target forces were different. Third, within each
target-force combination, the forces produced by the two hands were
positively correlated with each other. The performance of the two
callosotomy patients was qualitatively the same, and compared to
college undergraduates, they showed enhanced indices of
force-coupling. The preserved force-coupling contrasts with the
striking lack of coupling in the spatial domain that these patients
demonstrate in bimanual movements tasks. A subcortical locus of
force-coupling between the hands is a likely explanation of these
results.
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