Individual sensorimotor adaptation characteristics are independent across orofacial speech movements and limb reaching movements

Sensorimotor adaptation is critical for human motor control but shows considerable interindividual variability. Efforts are underway to identify factors accounting for individual differences in specific adaptation tasks. However, a fundamental question has remained unaddressed: Is an individual's capability for adaptation effector system specific or does it reflect a generalized adaptation ability? We therefore tested the same participants in analogous adaptation paradigms focusing on distinct sensorimotor systems: speaking with perturbed auditory feedback and reaching with perturbed visual feedback. Each task was completed once with the perturbation introduced gradually (ramped up over 60 trials) and, on a different day, once with the perturbation introduced suddenly. Consistent with studies of each system separately, visuomotor reach adaptation was more complete than auditory-motor speech adaptation (80% vs. 29% of the perturbation). Adaptation was not significantly correlated between the speech and reach tasks. Moreover, considered within tasks, 1) adaptation extent was correlated between the gradual and sudden conditions for reaching but not for speaking, 2) adaptation extent was correlated with additional measures of performance (e.g., trial duration, within-trial corrections) only for reaching and not for speaking, and 3) fitting individual participant adaptation profiles with exponential rather than linear functions offered a larger benefit [lower root mean square error (RMSE)] for the reach task than for the speech task. Combined, results suggest that the ability for sensorimotor adaptation relies on neural plasticity mechanisms that are effector system specific rather than generalized. This finding has important implications for ongoing efforts seeking to identify cognitive, behavioral, and neurochemical predictors of individual sensorimotor adaptation.