Do accuracy requirements change bimanual and unimanual control processes similarly?

Unimanual (left and right limbs) and bimanual (in-phase) reciprocal aiming tasks were tested to determine if the control processes used to perform the unimanual aiming tasks were also present in bimanual aiming tasks. Participants were asked to move a cursor as quickly and accurately as possible between the two targets presented in a Lissajous feedback display. The size of the targets created indexes of difficulty (ID) of 3, 4, 5, and 6 and the position of the targets created bimanual and unimanual conditions. The results indicated that, as ID increased, the end-effectors’ motion gradually switched from a cyclical to a more discrete motion for both unimanual and bimanual aiming tasks. However, the transition in control processes (i.e., the transition between cyclical and more discrete motions) tended to occur at a lower ID for the bimanual than the unimanual aiming tasks. Results also indicated that at ID6, bimanual aiming tasks were performed slower, more variable, and right limb dwelled at the targets longer than in the unimanual aiming task. No differences in performance were detected between the unimanual (left and right) and bimanual conditions at IDs 3–5. In terms of bimanual coordination, increasing the accuracy requirement resulted in decreased relative phase bias, but not more stable coupling between the two limbs.