Spatial conceptual influences on the coordination of bimanual actions: When a dual task becomes a single task

When the left and right hands produce 2 different rhythms simultaneously, c oordination of the hands is difficult unless the rhythms can be integrated into a unified temporal pat tern. In the present study, the authors investi gated whether a similar account can be applied to the spatial domain. Parti cipants (N = 8) produced a movement trajectory of semicircular form in sing le-limb and bimanual conditions. In the bimanual tasks, 1 limb moved above the other in the frontal plane. Bimanual unified tasks were constructed so that the spatial paths to be produced by the ? limbs could be easily concep tualized as parts of a unified circle pattern. Bimanual distinct tasks avai led a less obvious spatial pattern that would unify the 2 tasks. Performanc e of the spatial patterns was more accurate in the unified task, despite si milar demands placed on the coordination dynamics between the limbs in the 2 cases (e.g., the phase relations). The authors conclude that a dual task becomes a single task, and interlimb interference is reduced, when the spat ial patterns produced by the 2 hands form a geometric arrangement that can be conceptualized as a unified representation.