Different control strategies drive interlimb differences in performance and adaptation during reaching movements in novel dynamics

Abstract

Humans exhibit lateralization such that most individuals typically show a preference for using one arm over the other for a range of movement tasks. The computational aspects of movement control leading to these differences in skill are not yet understood. It has been hypothesized that the dominant and non-dominant arms differ in terms of the use of predictive or impedance control mechanisms. However, previous studies present confounding factors that prevented clear conclusions: either the performances were compared across two different groups, or in a design in which asymmetrical transfer between limbs could take place. To address these concerns, we studied a reach adaptation task during which healthy volunteers performed movements with their right and left arms in random order. We performed two experiments. Experiment 1 (18 participants) focused on adaptation to the presence of a perturbing force field and Experiment 2 (12 participants) focused on rapid adaptations in feedback responses. The randomization of the left and right arm led to simultaneous adaptation, allowing us to study lateralization in single individuals with symmetrical and minimal transfer between limbs. This design revealed that participants were able to adapt control of both arms, and that adaptation was greater in the dominant arm than in the non-dominant. We also observed that the non-dominant arm showed a different control strategy compatible with robust control when adapting to the force field perturbation. EMG data showed that these differences in control were not caused by differences in co-contraction across the arms. Thus, instead of assuming differences in predictive or reactive control schemes, our data show that in the context of optimal control, both arms can adapt, and that the non-dominant arm uses a more robust, model-free strategy likely to compensate for less accurate internal representations of movement dynamics.

Analysis of Differences in Single-Joint Movement of Dominant and Non-Dominant Hands for Human-like Robotic Control

“…This result is consistent with that of a previous study [44], with a tracer's initial peak speed and the corresponding initial peak time showing no difference in FF control of the dominant and non-dominant hands. Therefore, a difference in the performance of both arms in FF control [44,45] may not be attributable to the differences in muscle torque control for multi-joint movements.…”