Simulating a neural cross-talk model for between-hand interference during bimanual circle drawing

Studies on drawing circles with both hands in the horizontal plane have sho wn that this task is easy to perform across a wide range of movement freque ncies under the symmetrical mode of coordination, whereas under the asymmet rical mode (both limbs moving clockwise or counterclockwise) increases in m ovement frequency have a disruptive effect on trajectory control and hand c oordination. To account for these interference effects, we propose a simpli fied computer model for bimanual circle drawing based on the assumptions th at (1) circular trajectories are generated from two orthogonal oscillations coupled with a phase delay, (2) the trajectories are organized on two leve ls, "intention" and "motor execution", and (3) the motor systems controllin g each hand are prone to neural cross-talk. The neural cross-talk consists in dispatching some fraction of any force command sent to one limb as a mir ror image to the other limb, assuming predominating coupling influences fro m the dominant to the nondominant limb, the simulations successfully reprod uced the main characteristics of performance during asymmetrical bimanual c ircle drawing with increasing movement frequencies, including disruption of the circular form drawn with the nondominant hand, increasing dephasing of the hand movements, increasing variability of the phase difference, and oc casional reversals of the movement direction in the nondominant limb. The i mplications of these results for current theories of bimanual coordination are discussed.