# A Personalised Emotion-Based Model for Relaxation in Virtual Reality
###### Abstract  
One of the most frequent health problems is stress. It has been linked to negative effects on employee well-being in many occupations, and it is considered responsible for many physical and psychological problems. Traditional in-person relaxation therapy has proven to be effective in reducing stress. However, it has some drawbacks such as high cost, required infrastructure and the need for qualified trainers. Relaxation therapy in Virtual Reality (VR) tries to solve these problems. However, one aspect has received little attention, that is personalised therapy. Indeed, while many studies show the need for patient-tailored relaxation exercises, little existing work focuses on personalised VR content. One reason for this is the complexity of recognising emotions, which is required for emotion-based adaptive VR. In this work, a method for adapting VR content to the emotional state of the user is presented. This model has been applied in a VR relaxation therapy application, which adapts to the user's emotional state utilising a heuristic optimiser. Simulations have proven the performance and usability of the emotion model. Additionally, this paper explores the impact of the order in which adaptations are performed on the effectiveness of the relaxation experience.  
Keywords:relaxation therapy; virtual reality; personalisation; emotions modelling +
Footnote †: journal: Medical  
Virtual Reality (VR) can provide the required effectiveness for various kinds of therapy [9]. By fully immersing the user in a new environment, they can virtually teleport to a more suited location for relaxation. This immersion eliminates the many distracting factors of the real environment. Furthermore, it reduces costs, as the user only requires a Head Mounted Display (HMD) and an Internet connection, instead of the dedicated trainers and infrastructures of traditional relaxation therapy. Finally, where real-life relaxation therapy adopts a personally tailored approach, the VR counterpart should follow in this path. Indeed, given its individualistic essence, VR has the potential to provide personalised solutions to the users. However, due to the absence of a trainer or therapist, the personalisation needs to be automated by a computer system.  
In previous research, the potential of personalised VR for relaxation have been explored. For example, [PERSON] et al. [10] proposed a user-centered VR experience for general relaxation. However, current solutions are either too tailored for a very particular user-type or very generic thus decreasing their effectiveness. Furthermore, they tend to rely fully on sensor data and subjective user evaluations. While employing user data aids to tailor and adapt the applications, the variability makes it difficult to create models that could be utilised for a broad range of users. For such cases, there is a need for objectively driven models able to fit a broad range of users.  
This work proposes a personalised and adaptive VR model for relaxation therapy in VR. Employing a broad set of possible adaptations in a Virtual Environment (VE), our approach models relaxation as a function of three other emotions, namely stress, arousal and fear. We have evaluated our approach both for relaxation indoor and outdoor environments and for a wide range of users. Our results illustrate the potential of employing objective models for personalisation approaches in VR.  
The remainder of this paper is structured as follows. Section 2 describes the state of the art on VR for relaxation therapy. Section 3 introduces our method providing all the equations and theoretical reasoning behind the definition of the model. Sections 4 and 5 present the evaluation setup details and evaluation results. Finally, Section 6 concludes this paper.