Speed differences during two-handed tasks: bimanual versus intermanual coordination and the effect of practice

Prior research has shown that some two-handed tasks are completed faster when using the dyadic, intermanual coordination mode (two people each using one hand to complete a two-handed task) compared to the normal, bimanual coordination mode (one person using two-hands). However, this so-called “intermanual speed advantage” has been found to disappear after bimanual practice. Research suggests that these performance differences may depend on fundamental characteristics of each coordination mode that facilitate or impede speed during two-handed tasks. To investigate underlying human factors that affect speed, a task was constructed to exploit ostensible bimanual limitations: between-hand coupling and visuomotor coupling. Additionally, it was hypothesized that speed during two-handed tasks is associated with simultaneous, goal-directed movements (SGDMs) of the limbs, and that the bimanual limitations restrict the ability to make these movements during unpracticed task performance. It was further hypothesized that the intermanual speed advantage would disappear following bimanual practice. Indeed, the intermanual speed advantage found in prior literature was replicated during an unpracticed task and was not present following bimanual practice. Results suggest that the explanatory measures (between-hand coupling, visuomotor coupling, and SGDMs) provide a simple explanation of speed during two-handed tasks as compared to previously offered explanations based on shared task knowledge. Furthermore, previous bimanual practice increased performance (as evidenced by speed and results for most of the explanatory measures), which was consistent with hypotheses. The findings have implications for theories of motor control and applications that require individual and cooperative manual coordination, such as teleoperation and laparoscopy.