Immediate Compensation for Variations in Self-generated Coriolis Torques 4

22 We have previously shown that the Coriolis torques that result when an arm movement is 23 performed during torso rotation do not affect movement trajectory. Our purpose here was to 24 examine whether torso motion induced Coriolis and other interaction torques are counteracted 25 during a turn and reach (T&R) movement when the effective mass of the hand is augmented, and 26 whether the dominant arm has an advantage in coordinating intersegmental dynamics as 27 predicted by the dynamic dominance hypothesis (Sainburg 2002). Subjects made slow and fast 28 T&R movements in the dark to just extinguished targets with either arm, while holding or not 29 holding a 454 g object. Movement endpoints were equally accurate at both speeds, with either 30 hand, and in both weight conditions, but subjects tended to angularly undershoot and produce 31 more variable endpoints for targets requiring greater torso rotation. There were no changes in 32 endpoint accuracy or trajectory deviation over repeated movements. The dominant right arm was 33 more stable in its control of trajectory direction across targets while the non-dominant left arm 34 had an improved ability to stop accurately on the target for higher levels of interaction torques. 35 The trajectories to more eccentric targets were straighter when performed at higher speeds but 36 slightly more deviated when subjects held the weight. Subjects did not slow their torso velocity 37 or change the timing of the arm and torso velocities when holding the weight, although there was 38 a slight decrease in their hand velocity relative to the torso. The delay between the onsets of torso 39 and finger movements was almost twice as large for the right arm than the left, suggesting the 40 right arm was better able to account for torso rotation in the arm movement. Holding the weight 41 increased the peak Coriolis torque by 40% at the shoulder and 45% at the elbow and, for the 42 most eccentric target, the peak net torque by 12% at the shoulder and 34% at the elbow. In 43 accordance with the dynamic dominance hypothesis (Sainburg 2002), the right arm exhibited an 44