Casadio, M. | bioRxiv Science

bioRxiv2018

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.

neuroscience↗

bioRxiv2017

High variability impairs motor learning regardless of whether it affects task performance

Motor variability plays an important role in motor learning, although the exact mechanisms of how variability affects learning is not well understood. Recent evidence suggests that motor variability may have different effects on learning in redundant tasks, depending on whether it is present in the task space (where it affects task performance), or in the null space (where it has no effect on task performance). Here we examined the effect of directly introducing null and task space variability using a manipulandum during the learning of a motor task. Participants learned a bimanual shuffleboard task for 2 days, where their goal was to slide a virtual puck as close as possible towards a target. Critically, the distance traveled by the puck was determined by the sum of the left and right hand velocities, which meant that there was redundancy in the task. Participants were divided into five groups - based on both the dimension in which the variability was introduced and the amount of variability that was introduced during training. Results showed that although all groups were able to reduce error with practice, learning was affected more by the amount of variability introduced rather than the dimension in which variability was introduced. Specifically, groups with higher movement variability during practice showed larger errors at the end of practice compared to groups that had low variability during learning. These results suggest that although introducing variability can increase exploration of new solutions, this may come at a cost of decreased stability of the learned solution.

neuroscience↗