# From Patient to Musician: A Multi-Sensory Virtual Reality Rehabilitation Tool for Spatial Neglect
## 2 Background
### VR for Rehabilitation  
In Virtual Reality, the user is placed in a completely computer-generated three-dimensional simulation, where they can look around and interact with their environment using devices such as a Head Mounted Display (HMD) and gloves or controllers, to create an immersive experience. VR has long since found its place in the world of gaming and entertainment. Nevertheless, VR is increasing in popularity in a clinical setting. A tool for the rehabilitation of children with dystonic cerebral palsy [59], limb pain alleviation [60] and VR exposure therapy for anxiety disorders [61] are just a few examples of the clinical applications of VR [62; 63; 64; 65; 66; 67]. Other mixed reality tools, such as Augmented Reality (AR), have also found their way into clinical applications, e.g., neurosurgery [68; 69]. VR has many advantages over traditional rehabilitation techniques. First, VR systems can augment and manipulate the interaction of the user with the environment and can quantitatively monitor it, promoting the functional recovery of the patient [70]. Second, opposed to traditional treatment options, VR is modular, enabling the tailoring of the treatment to the patient's needs and physical or cognitive capabilities. Third, there is no need for a clinician as the system can monitor the performance of the patient and quantify how well a task is being performed and give feedback accordingly. This consequently increases the potential for at-home rehabilitation. Lastly, the virtual environment is oftenmore immersive and enjoyable than conventional treatments, which leads to the patient more actively participating and an increased positive attitude towards the treatment, which increases the overall quality of life of the patient [71]. However, the use of VR introduces several disadvantages as well. First, the immersion aspect can provoke cyber sickness in some, leading to the incompletion of the treatment or an unenjoyable experience. Nevertheless, a large portion of these side effects can be managed by taking appropriate precautions, such as excluding patients prone to motion sickness and following post-immersion procedures [72]. Second, there are studies investigating the spatial perception of distance [73,74] and orientation [75] in VR environments. These studies have found that subjects perceive distances differently in VR than in real life, while the perception of orientation remains the same in VR. This should be carefully considered in therapy use cases where the perception of the user is important. Third, the design of a new VR tool for a clinical setting should always be based on an informed theoretical foundation [76]. Finally, although the cost of VR devices has decreased in recent years, the initial equipment cost is still far greater than traditional pen-and-paper tools, which can be a barrier to their adaption in a clinical setting, especially in lower-income countries [77,78]. As mentioned, VR is becoming more and more present in healthcare applications. On of these applications is the rehabilitation of spatial neglect [79, 80, 81, 82, 83]. As there is currently no gold standard for the rehabilitation of USN, new VR interventions can flourish. Moreover, VR provides the opportunity to address and support the multi-sensory characteristics of the syndrome as it incorporates not only visual but also other sensory stimuli. Tactile feedback can be provided using haptic feedback through controllers, and the headphones integrated in a HMD provide auditory stimuli. Moreover, three-dimensional sound can be simulated such that sound is linked to a certain location in space. The use of VR in rehabilitation for USN can hereby accommodate the demand for multi-sensory intervention techniques. Next, clear visual and auditory progress markers motivate the user and help the rehabilitation process. Furthermore, the use of VR provides more enjoyment of the therapy and increases overall motivation.