AbstractResearch has suggested that bimanual movements are not the sum of two unimanual movements, but they reflect the integration of two unimanual movements into a bimanual movement. Bimanual asymmetric movements in choice RT tasks take longer to prepare than symmetric movements, and this cost is likely caused by unifying both arms into a single bimanual movement. The purpose of this study was to investigate the process of "integrating" unimanual movements into a bimanual movement and "de-integrating" bimanual movements into unimanual movements during movement preparation. We predicted that integrating two different unimanual movements into a single bimanual asymmetric movement would take more time than when two similar movements are combined into a bimanual symmetric movement. Conversely, the de-integration of a bimanual asymmetric movement would take more time than a bimanual symmetric movement. In both studies, each block consisted of two unimanual movements and one bimanual movement. In the integration study, 80% of trials were unimanual and 20% were bimanual. The bimanual movements were symmetric or asymmetric and they were the combination of the two unimanual movements or the opposite. In the de-integration study, 80% of trials were bimanual and 20% were unimanual. The unimanual movements were one arm of the bimanual movement or one of the opposite. In both studies there were preparation costs to integrate or de-integrate bimanual asymmetric movements and the opposite movements. These results support that bimanual movements are the integration of two unimanual movements and that asymmetric movements take longer to integrate (and de-integrate) than symmetric ones.
Acknowledgments: Supported by the Natural Sciences and Engineering Research Council of Canada