Limit-push training reduces motor variability.

Variability in human motor control has been a long observed phenomenon, which has come to be known by some as repetition without repetition. There are several explanations for this. One such explanation asserts that many equally optimal solutions exist for accomplishing the same task that naturally allows choices in how it can be successfully executed. The aim of this study was to determine whether variability could be conditioned within an invisible subspace, using visual and force feedback. We utilized a novel haptic-graphic boundary-oriented environment to condition motor variability. Subjects reduced the variability of their movements, such that action predominated within a subspace determined apriori; while the untreated group did not. These results show encouraging preliminary evidence that neural rehabilitative haptic-graphic interfaces can condition human motor variability. This type of training may benefit neurologically impaired individuals, who exhibit the commonly seen motor deficits of large trial to trial variability, such as victims of stroke and traumatic brain injury.