Abstract
Asymmetric, target-directed, bimanual movements take longer to prepare than symmetric movements (Diedrichsen et al. 2006; Heuer and Klein 2006 Psychol Res). Symmetric movements have the same starting locations, movement amplitudes, and target locations. Asymmetric movements typically have the same starting locations with different amplitudes and target locations. The preparation cost for asymmetric movements may, therefore, be related to the specification of different amplitudes, target locations, or both. Two studies have investigated the effects of these parameters, but their protocols were confounded by the number of movement choices (Heuer and Klein 2006 J Mot Behav) or two different symbolic cues (Weigelt 2007). The goal of this study was to determine which parameters contribute to interference during the preparation of bimanual movements. Thirty participants performed bimanual reaching movements that varied in terms of the symmetry/asymmetry of starting locations, amplitudes, and target locations. Reaction time costs were examined by comparing movements that had one asymmetric parameter to movements with all symmetric parameters. We observed significant reaction time costs (~13ms) for movements with asymmetric amplitudes, and no significant costs for movements with symmetric amplitudes. These effects were independent of the symmetry/asymmetry of the starting and target locations. Reaction time savings were examined by comparing movements that had one symmetric parameter to movements with all asymmetric parameters. We observed significant savings (~9ms) for all movements with one symmetric parameter. Taken together, these results suggest that any one symmetric parameter is sufficient to reduce interference during preparation, and asymmetric amplitudes may result in the largest interference.
