The Impact of Implicit and Explicit Feedback on Performance and Experience during VR-Supported Motor Rehabilitation

Top left: participants were exposed to the VR simulation while using the gait robot (lokomat). Top center: avatar embodiment. Virtual handles (in light blue) mimic the position and shape of the real physical handles to generate plausible hand actions during walking. Top right: explicit visual feedback signaled at the trainer’s feet. Bottom left: same explicit feedback signaled at the patient’s feet. Bottom center: alternative feedback example. Bottom right: emoticon feedback.

Abstract

This paper examines the impact of implicit and explicit feedback in Virtual Reality (VR) on performance and user experience during motor rehabilitation. In this work, explicit feedback consists of visual and auditory cues provided by a virtual trainer, compared to traditional feedback provided by a real physiotherapist. Implicit feedback was generated by the walking motion of the virtual trainer accompanying the patient during virtual walks. Here, the potential synchrony of movements between the trainer and trainee is intended to create an implicit visual affordance of motion adaption. We hypothesize that this will stimulate the activation of mirror neurons, thus fostering neuroadaptive processes. We conducted a clinical user study in a rehabilitation center employing a gait robot. We investigated the performance outcome and subjective experience of four resulting VR-supported rehabilitation conditions: with/without explicit feedback, and with/without implicit (synchronous motion) stimulation by a virtual trainer. We further included two baseline conditions reflecting the current NonVR procedure in the rehabilitation center. Our results show that additional feedback generally resulted in better patient performance, objectively assessed by the necessary applied support force of the robot. Additionally, our VR-supported rehabilitation procedure improved enjoyment and satisfaction, while no negative impacts could be observed. Implicit feedback and adapted motion synchrony by the virtual trainer led to higher mental demand, giving rise to hopes of increased neural activity and neuroadaptive stimulation.

Publication
IEEE Conference on Virtual Reality and 3D User Interfaces (IEEE VR) 2021
The authors give special thanks to the participants and therapy team of the NiB Rehabilitation Center (Cologne, Germany) for supporting this research. We wish to thank Julian Müller for his contributions to the development of the VR simulation. This work was supported in part by the XR-Hub Würzburg (XR-Hub Bavaria) funding from the Bavarian State Ministry for Digitalization.