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UBC Theses and Dissertations

Information processing of bimanual reaching movements Blinch, Jarrod Paul George


The information processing of bimanual reaching movements was investigated in this thesis. All of the studies tested symmetric and asymmetric bimanual reaching movements that were made to targets as quickly and accurately as possible. The duration of movement preparation was measured by reaction time (RT). Study one found that bimanual asymmetric movements had longer preparation than bimanual symmetric movements. Donders’ subtraction method was used to isolate this bimanual asymmetric cost to a stage, or stages, of movement preparation that are unique to choice RT tasks; these included target discrimination, response selection, and response programming. Many different movement parameters could cause bimanual asymmetric costs. The results from study two suggested that the relative contribution of three parameters to the asymmetric cost, from most to least important, was movement amplitudes, target locations, and then startling locations. The relationship between unimanual and bimanual movements was tested in the third study by precuing the target for the left arm of a bimanual movement. RT and the start-react effect were used to determine how movement preparation changed. These measures suggested: 1) that the precued movement was not fully programmed but partially programmed before the imperative stimulus, and 2) that the asymmetric cost was caused by increased processing demands on response programming. Overall, the results supported that bimanual movements are not the sum of two unimanual movements; instead; the two arms of a bimanual movement are unified into a functional unit. When one target is precued, this critical unification likely occurs during response programming. Study four used the additive factors method to determine which stages of movement preparation contributed to the asymmetric cost when both targets were cued by the imperative stimulus. The results supported that the asymmetric cost was caused by increased processing demands on response selection. Target discrimination and response programming – contrary to previous hypotheses – did not contribute to the asymmetric cost. The critical process of bimanual unification likely depends on how the task is presented and conceptualised. It occurs during response selection when both targets are cued by the imperative stimulus, and it is deferred to response programming when one target is precued.

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