Comparing movement preparation of unimanual, bimanual symmetric, and bimanual asymmetric movements.

The goal of this study was to determine the process or processes most likely to be involved in reaction-time costs for spatially cued bimanual reaching. We used reaction time to measure the cost of bimanual symmetric movements compared to unimanual movements (a bimanual symmetric cost) and the cost for bimanual asymmetric movements compared to symmetric movements (a bimanual asymmetric cost). The results showed that reaction times were comparable for all types of movements in simple reaction time; that is, there was neither a bimanual symmetric cost nor an asymmetric cost. Therefore, unimanual, bimanual symmetric, and bimanual asymmetric movements have comparable complexity during response initiation. In choice conditions, there was no bimanual symmetric cost but there was a bimanual asymmetric cost, indicating that the preparation of asymmetric movements is more complex than symmetric movements. This asymmetric cost is likely the result of interference during response programming.