Spatial topological constraints in a bimanual task.

Previous research has shown that the concurrent performance of two manual tasks results in a tight temporal coupling of the limbs. The intent of the present experiment was to investigate whether a similar coupling exists in the spatial domain. Subjects produced continuous drawing of circles and lines, one task at a time or bimanually, for a 20 s trial. In bimanual conditions in which subjects produced the circle task with one hand and the line task with the other, there was a clear tendency for the movement path of the circle task to become more line-like and the movement path of the line task to become more circle-like, i.e., a spatial magnet effect. A bimanual circle task and a bimanual line task did not exhibit changes in the movement path when compared to single-hand controls. In all bimanual conditions, the hands were tightly temporally locked. The evidence of temporal coupling and concomitant accommodation in the movement path for the conditions in which the hands were producing different shapes suggests that spatial constraints play a role in the governance of bimanual coordinated actions.