A task-dependent effect of memory and hand-target on proprioceptive localization.

We examine whether the task goal affects the accuracy and precision with which participants can localize an unseen hand. Proprioceptive localization was measured using three different tasks: two goal-directed movement tasks (reaching to and reproducing final hand-target location) and a perceptual estimation task in which participants judged the location of the hand-target relative to visual references. We also assessed whether proprioceptive localization in these different tasks is affected by localization from memory, the hand-target being localized (left or right) or the movement path of the proprioceptive target (9 paths, derived from combinations of starting and final hand-target positions). We found that participants were less precise when reaching from memory, but not when reproducing or estimating remembered final hand-target location. Participants also misperceived the felt location of their hands, judging their left hand to be more leftward and their right hand to be more rightward when reaching to and when estimating final hand-target location, but not when reproducing hand-target location. The movement path of the proprioceptive target did not affect localization, regardless of the task goal. Overall, localization seems poorer when proprioception is used to guide a reach with the opposite hand, particularly from memory, and best when merely reproducing the proprioceptive target site. This may have an important application in neuro-rehabilitation, whereby one task may better establish or re-establish important or failing sensory connections.