Different But Complementary Motor Functions Reveal an Asymmetric Recalibration of Upper Limb Bimanual Coordination

Bimanual coordination, fundamental to human motor control, typically involves the execution of different functions by the two limbs (e.g., opening a jar). Previous research has largely investigated bimanual control through simple coordination tasks in which the limbs perform similar movements (e.g., finger tapping); however, few studies have specifically examined coordination when the two limbs perform different yet complementary functions. In the current study, participants performed point-to-point movements of a rectangular cursor, where one limb controlled cursor trajectory and the other rotated a knob to match a target orientation. Participants (N = 116, 76 female, 1 nonbinary; 92% right-handed) were divided into four groups and completed the task with a visual feedback gain perturbation (an increase or decrease) applied either to the cursor trajectory or orientation. Our results showed rapid adaptation to perturbations of visual feedback of the movement trajectory, affecting both the perturbed limb controlling the trajectory and the unperturbed limb controlling the orientation. Conversely, perturbation to the visual orientation feedback primarily only influenced the perturbed limb controlling orientation, with minimal impact on movement trajectory metrics. Importantly, these results were independent of reaching amplitude, duration, and limb dominance. In addition, we assessed the temporal coordination between the two limbs and found that perturbations in visual trajectory feedback led to significant changes in limb coordination, whereas no notable difference was observed for perturbations of orientation. These findings indicate asymmetries in bimanual motor recalibration dependent on the perturbed aspect of visual feedback (orientation vs trajectory), suggesting differences in underlying neural mechanisms and interhemispheric communication.