Abstract
The formation of internal models is one mechanism through which motor learning takes place. Internal models can be formed either of the inertial properties of one’s own arm or of inertial properties of external objects. But do internalized models modify movements only in the context in which they were learned or do they generalize across contexts? There exists some disagreement in the literature over this idea, possibly due to the different paradigms used in these experiments. To examine the effects different testing contexts exert on motor learning, participants performed a point-to-point reaching task while grasping a robot manipulandum that applies a force perturbation of 4.0 N•m/s. Single null field catch trials were interspersed throughout the task, during which participants moved the handle of a grasped manipulandum to a visual target, moved the detached handle of the manipulandum, or reached in free space. Participants who reached in free space exhibited minimal aftereffects, while participants who reached with the attached handle experienced the maximum aftereffects. Those who reached with the detached handle experienced intermediate aftereffects, although not significantly different from free space reaching. Upon return to the manipulandum, participants who reached in free space did not retain memory of the force, while those who reached with the detached handle did. Reaching with the attached handle led to intermediate reduction in retention, although not significantly different than free or detached handle. These results show that subtle changes to the testing environment can have a dramatic effect on a learned motor adaptation, which suggests that motor learning results in temporary adaptations to object dynamics rather than the retention of finite models.