Concurrent adaptation to force fields and visual rotations

An important issue in sensorimotor adaptation is what drives adaptation, and whether different types of perturbations are mediated by different adaptation mechanisms. Here we assess whether any interference is observed among the joint adaptation to visual (i.e. kinematic) and force (i.e. dynamic) perturbations. Subjects adapted their reaching movements to rotations of the display. During adaptation, we perturbed their movements with a rotational force field, whose direction was either the same or the opposite of the visual perturbation (R+F and R-F groups). In the two groups, we compared the outcomes of both adaptation modalities. In addition, we analyzed the dynamics of the adaptation processes in terms of a number of linear dynamical models, based on different assumptions. We conclude that the two adaptation processes occur largely in parallel, with little interaction, and exhibit similar time constants, which suggests common underlying memory mechanisms. In addition, we found that subjects in the R+F group exhibit a significantly smaller hand compliance, which suggests that the different combinations of disturbances affect the regulation of arm impedance.