Vibrotactile feedback improves performance in 3-coupled trimanual tasks

Human Movement Augmentation (HMA) provides users with the means (e.g., supernumerary robotic limbs) to enhance their motor abilities with additional degrees of freedom, enabling trimanual tasks among other feats. While recently researchers have shown that humans may be capable of performing trimanual activities, the studies conducted so far on augmented tasks neglected a fundamental aspect of the sensorimotor loop, i.e., the sensory feedback related to supernumerary limbs. Hence, we investigated how supplementary vibrotactile feedback can impact on the performance while completing a trimanual task. We engaged participants in trimanual reaching tasks that could be completed either alone or in collaborating dyads, by using virtual effectors that could be differently coupled together through virtual elastic links. Performance indexes (i.e., score, fails, smoothness and effectors' coupling) demonstrated that vibrotactile feedback significantly improves participants' performance when the three effectors were virtually coupled together, and especially when participants were acting alone. This result is particularly relevant in the augmentation scenario, as it suggests that supplementary feedback can significantly aid the user who single-handedly controls a supernumerary limb.