Investigating the Benefits of Multivariable Proprioceptive Feedback for Upper-Limb Prostheses

Restoration of somatosensory feedback can improve prosthesis control and user experience. Although modern prosthesis allows movement in multiple degrees of freedom, few studies have attempted to restore multiple proprioceptive feedback variables to give the user awareness of the prosthesis state without excessive visual attention. This study presents and evaluates a feedback system containing four vibration motors embedded in the prosthesis socket to convey hand aperture or wrist rotation angle during sequential prosthesis control. Ten able-bodied and two amputee subjects performed a functional task that involved manipulating fragile objects with varying compliance (with vibrotactile and/or visual or neither). The results indicated that with vibrotactile feedback alone, able-bodied subjects performed the grasping and rotation phases of the task with almost the same quality as with visual feedback (no statistically significant difference). In addition, vibrotactile feedback significantly outperformed incidental feedback during wrist rotation control. Similar findings were observed for the amputee subjects. All subjects rated vibrotactile feedback as useful, reliable, and easy to perceive and exploit. Exploiting the vibrotactile feedback, however, required more time than for visual feedback. In conclusion, the proposed feedback system represents an efficient and practical solution to facilitate object manipulation in multiple degrees of freedom, even when visual feedback is not fully available.