Forefeel the Move: Investigating Proprioceptive Feedback for Communicating Imminent Motions of Body-actuating Systems

Systems actuating the body can proactively assist users in diverse tasks. However, unexpected body actuation may pose safety risks. We propose proprioceptive feedback to inform users about an imminent actuation before the system takes control. In a user study, we compare different proprioceptive cues that either interrupt or augment user motion to convey (1) solely that a body actuation is imminent, (2) its direction, or (3) its target. To enable a controlled investigation, we confined the cues to one degree-of-freedom joints and implemented them in an elbow exoskeleton. The results show that all cues are highly noticeable, offering an integrated feedback channel; yet, their effectiveness in communicating direction and target differed: While cues that augmented user motion were more accurate and preferred, disruptive cues enabled faster but less accurate interpretations. Furthermore, our analysis revealed that proprioceptive feedback enhanced the expressiveness of the conveyed information and user’s aspirations for adaptive feedback.