Impact of Visual Feedback Configurations in a Task-Oriented Immersive Virtual Reality Mirror Therapy

Mirror Therapy is a form of upper limb therapy in stroke, which consists on showing the mirrored symmetric movement of the unimpaired side using a mirror placed in the medial sagittal plane. The illusion of movement corresponding to the impaired extremity could facilitate neuroplasticity, and assists patients in regaining certain lost motor functions. Recent studies have shown the potential and benefit of translating this effective therapy in an immersive virtual reality (VR) environment, using head mounted display and hand tracking systems. This work investigates the feasibility to use myoelectric control in an immersive VR environment for the mirror therapy to accomplish a funtional task. Surface electromyography sensors were used to measure muscle activation and detect user intention to perform grasping actions in two visual feedback configurations: unimanual and bimanual. Even though in both conditions the virtual mirrored hand is controlled by the healthy hand, the latter creates the illusion that two functional hands cooperate for grasping. A total of 18 healthy subjects participated in the evaluation of the environment, control method and a comparison between the two configurations. This includes self-rating surveys and performance metrics. Results from the Simulator Sickness Questionnaire showed negligible adverse symptoms related to the use of the VR-application proposed. Positive outcomes from the System Usability Scale and Presence Questionnaire affirmed its feasible as a form of therapy for the rehabilitation of hemiparetic stroke patients. Although the adapted Box and Blocks Test proved immediate training-induced learning, performance measures revealed no significant distinctions between visual feedback configurations.