| Summary: | When a person performs an arm movement that requires concurrent activity of the
contralateral arm, it is common to observe a decrement in performance relative to when the
same task is performed in isolation (Ohtsuki, 1994). Thus, if a task requires a rapid
movement of one arm, that movement will, in general, be executed more quickly compared
with a condition where the opposite arm is moved simultaneously (Fowler et al., 1991;
Marteniuk & MacKenzie, 1980). Reaction time is similarly affected when simultaneous
bilateral actions are performed, with bilateral movements requiring more time for movement
initiation (Anson & Bird, 1993; Ohtsuki, 1994). Recently it has been suggested that the
increase in reaction time accompanying bilateral movements might reflect an inhibitory
interaction between the motor cortexes of the left and right hemispheres through the corpus
callosum, resulting in an increase in the time required for muscle activation (Ohtsuki, 1994).
Recent studies have provided support for this interpretation (Meyer & Voss, 2000; Taniguchi
et al., 2001).
Despite empirical support, however, a number of studies have yielded results
inconsistent with this proposal in that bilateral movements did not lead to increases in
reaction time (Anson & Bird, 1993; Swinnen et al., 1995). We (Garry & Franks, 2000) also
reported a failure for reaction time to increase with bilateral movements, but only when the
task demanded spatial precision of the right arm. When left arm precision was required,
reaction time increases were observed. Because our task involved proximal muscles, which
can be controlled through ipsilateral pathways (Berlucchi et al., 1994; Brinkman & Kuypers,
1973), we interpreted this result as evidence that under certain conditions (right arm
precision), bilateral movements can be initiated via a single hemisphere eliminating the inhibitory interhemispheric interactions that accompany bilateral movements. Although
experiments 1 and 2 were consistent with the predictions of this model, experiment 3 failed
to provide support. An alternative model involving premotor cortex mechanisms was
proposed. === Education, Faculty of === Kinesiology, School of === Graduate
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