Mixed Reality in Stroke Rehabilitation

Mixed reality (MR) has evolved from an extension of virtual and augmented reality into a clinically meaningful rehabilitation modality with growing empirical support. This chapter traces the historical development of extended reality technologies—from early stereoscopic displays and head-mounted systems to contemporary spatial-computing platforms—to situate MR within a broader technological and cultural lineage. Building on this foundation, we propose an evidence-based distinction between broad MR, defined along the reality–virtuality continuum, and narrow MR, which is constrained by three essential properties: precise perceptual co-registration between real and virtual elements, preservation of haptic or proprioceptive realism, and adaptive reciprocity that continuously links user behavior to digital feedback. Within this narrow MR framework, we delineate two major clinical subtypes. Tangible mixed reality (tMR) integrates physical manipulable objects with virtual overlays, offering high sensorimotor fidelity that is particularly suited for upper-limb training and fine-motor rehabilitation. Immersive spatial mixed reality (iMR) employs optical see-through head-mounted displays to deliver depth-aware, spatially registered holographic cues applicable to gait, balance, and cognitive–motor tasks. Synthesizing evidence from systematic reviews and stroke rehabilitation trials, we describe consistent moderate improvements in motor impairment, functional independence, movement quality, and patient engagement, along with emerging neurophysiological findings indicating plasticity within sensorimotor and frontoparietal networks. The chapter further examines underlying technical architectures, spatial mapping approaches, feedback design principles, patient selection criteria, and strategies for integrating MR into clinical workflows. Finally, we outline key future directions—including robotics integration, AI-driven adaptive progression, and neuroadaptive sensing—and argue that narrow MR constitutes a distinct, embodied therapeutic medium rather than a midpoint between VR and AR, offering a mechanistically grounded framework for next-generation rehabilitation.