Supplemental vibrotactile feedback of real-time limb position enhances precision of goal-directed reaching
We examined vibrotactile stimulation as a form of supplemental limb state feedback to enhance on-going control goal-directed movements. Subjects wore a two-dimensional vibrotactile display on their non-dominant arm while performing horizontal planar reaching movements with their dominant arm. The vibrotactile display provided feedback of hand position such that small hand displacements were more easily discriminable using vibrotactile feedback than with intrinsic proprioceptive feedback. When subjects relied solely on proprioceptive feedback to capture visuospatial targets, target capture performance was degraded by proprioceptive drift and an expansion of task space. By contrast, reach accuracy was enhanced immediately when subjects were provided vibrotactile feedback, and further improved over two days of training. Improvements reflected a resolution of proprioceptive drift which occurred only when vibrotactile feedback was active, demonstrating that the benefits of vibrotactile feedback are due in part to its integration into the ongoing control of movement. A partial resolution of task space expansion that persisted even when the vibrotactile feedback was inactive demonstrated that training with vibrotactile feedback also induced changes in movement planning. However, the benefits of vibrotactile feedback come at a cognitive cost. All subjects adopted a stereotyped, movement decomposition strategy wherein they attempted to capture targets by moving first along one axis of the vibrotactile display and then the other. For most subjects, this inefficient movement approach did not resolve over two bouts of training performed on separate days, suggesting that additional training is needed to fully integrate vibrotactile feedback into the planning and online control of goal-directed reaching.