The persistence of spatial interference after extended training in a bimanual drawing task.

Many studies of bimanual coordination have focused on the pervasive interference observed when people plan and produce non-symmetric movements. We investigated how the interference observed in one challenging bimanual task, simultaneously drawing non-symmetric three-sided squares (e.g., U and C), is modulated by practice. We assessed whether the benefits of practice were limited to the trained patterns or reflected the development of a more general ability for independently controlling movements of the two hands. We combined four orientations of a three-sided square, with one orientation assigned to each hand, to generate a set of 16 patterns. Participants were trained for six days with eight of the patterns. In the last two sessions, all 16 patterns were tested. The untrained patterns involved a shape that had not been practiced by one hand or a novel configuration of two practiced components. While a substantial reduction in inter-manual interference was observed over the extensive training period, participants remained much slower to plan incongruent shapes compared to congruent shapes. Incomplete generalization was observed when the new patterns were introduced. Planning time was shorter and accuracy higher for the trained patterns, but this effect was only observed in the first generalization session. There was little difference in performance between new patterns that involved an unpracticed shape or an unpracticed configuration. These results indicate that spatial interference was not eliminated with extensive practice. This persistent interference effect stands in contrast to the minimal interference observed when the gestures are conceptualized as a single action or do not involve the transformation of abstract spatial codes. The results suggest that a primary difficulty in bimanual drawing results from limitations in translating abstract goals into actions, a fundamental prerequisite for praxis.