Information processing of bimanual reaching movements

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.Education, Faculty ofKinesiology, School ofGraduat

On-line control of the limbs during bimanual reaching is independent with directly- and symbolically-cued target perturbations

Using both hands at the same time is an important ability of the human action system. This is referred to as bimanual coordination, and complex cases of coordination are often tested to reveal its limitations. A common limitation is that the limbs cannot make independent movements but are drawn to follow the same spatial trajectories with similar temporal properties. These examples of bimanual interference are called spatial and temporal interference. Another type of interference is seen in the initiation of bimanual reaching movements. When a reaching movement is directly-cued by illuminating the targets, the reaction time is the same for symmetric or asymmetric movements. However, the reaction time is longer for asymmetric compared to symmetric movements if they are symbolically-cued. The leading hypothesis for this reaction time cost is that the increased processing demands on response selection for symbolically-cued asymmetric movements results in bimanual interference (Diedrichsen, Hazeltine, Kennerley, & Ivry, 2001). In two experiments, we investigated the effect of this interference when it occurred as the result of a perturbation during a movement that required an on-line correction. We sought to determine if there was larger spatial interference in one limb when the other limb responded to a symbolically-cued on-line correction compared to a directly-cued correction. Participants made bimanual reaches to targets that were occasionally perturbed at movement onset. These perturbations required on-line corrections with one limb to the new target location. The new target location was indicated by illuminating the new target as a direct cue (experiments 1 and 2) or symbolically cueing the target with a colour change (experiment 1) or displaying the letter L or S (experiment 2). We found larger spatial interference for symbolically-cued on-line corrections compared to directly-cued corrections. Although there was greater interference with symbolic cues, the interference was small and transient with direct and symbolic cues. It was also subtle in comparison to spatial interference during preplanned bimanual reaches. Since a correction in one limb can be accomplished without a large or lasting effect on the other limb, we conclude that on-line control of the limbs during bimanual reaching is largely independent.Education, Faculty ofKinesiology, School ofGraduat