2168-2194 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JBHI.2018.2878846, IEEE Journal of Biomedical and Health Informatics JBHI-00629-2018 1 Abstract—Here we introduce the design and preliminary validation of a general-purpose architecture for affective-driven procedural content generation in Virtual Reality (VR) applications in mental health and wellbeing. The architecture supports seven commercial physiological sensing technologies and can be deployed in immersive and non-immersive VR systems. To demonstrate the concept, we developed the “The Emotional Labyrinth”, a non-linear scenario in which navigation in a procedurally-generated 3D maze is entirely decided by the user, and whose features are dynamically adapted according to a set of emotional states. During navigation, affective states are dynamically represented through pictures, music, and animated visual metaphors chosen to represent and induce affective states. The underlying hypothesis is that exposing users to multimodal representations of their affective states can create a feedback loop that supports emotional self-awareness and fosters more effective emotional regulation strategies. We carried out a first study to (i) assess the effectiveness of the selected metaphors in inducing target emotions, and (ii) identify relevant psycho-physiological markers of the emotional experience generated by the labyrinth. Results show that the Emotional Labyrinth is overall a pleasant experience in which the proposed procedural content generation can induce distinctive psycho-physiological patterns, generally coherent with the meaning of the metaphors used in the labyrinth design. Further, collected psycho-physiological responses such as electrocardiography, respiration, electrodermal activity, and electromyography are used to generate computational models of users’ reported experience. These models enable the future implementation of the closed loop mechanism to adapt the Labyrinth procedurally to the users’ affective state. Index Terms—Emotion regulation, physiological computing, physiology-driven VR, procedural content generation. I. INTRODUCTION uring the last two decades, Virtual Reality (VR) has been extensively applied to the treatment of mental health disorders [1], [2]. For instance, VR has been used in the treatment of anxiety disorders [3], [4], addictions [5], [6], and eating disorders [7]–[9], with very promising results. However, current VR-based treatments are mostly based on the use of pre- Manuscript received May 29, 2018. This work was supported by the Fundação para a Ciência e Tecnologia through UID/EEA/50009/2013, the European Commission through MACBIOIDI MAC/1.1.b/098, by Fondazione Cariplo within the project “Active Aging and Healthy Living”, and by the UCSC internal grant D1 “Tecnologie Trasformative”. Sergi Bermúdez i Badia is with the Madeira Interactive Technologies Institute and with the Faculdade de Ciências Exatas e da Engenharia, Universidade da Madeira, Funchal, Portugal (e-mail: sergi.bermudez@m- iti.org). Luis Velez Quintero was with the Madeira Interactive Technologies Institute, Funchal, Portugal (e-mail: levelezq@gmail.com). Mónica S. Cameirão is with the Madeira Interactive Technologies Institute and with the Faculdade de Ciências Exatas e da Engenharia, Universidade da Madeira, Funchal, Portugal (e-mail: monica.cameirao@m-iti.org). defined scenarios that are “fixed” for all patients, thus providing limited possibilities for personalizing treatment [10], [11]. In some cases, VR is combined with biofeedback strategies to inform the patient on his/her internal state. For instance, many virtual biofeedback approaches for mental health have in common the training of emotion regulation [12]–[18], as this is an essential feature in the treatment of several psychological conditions [19]. As an example, anxiety disorders and depression share impairments in emotion regulation. Namely, patients show a limited ability in suppressing negative emotions and/or re-evaluating emotional stimuli (reappraisal) to modify affective reactions [20]. Dysfunction in emotion regulation is also common in maladaptive and risky behaviors such as those related to eating (e.g., binge and fasting), as well as sexual disorders and substance abuse [21]–[23]. In the biofeedback approach, the patient is presented with information about changes in his/her physiological activity, i.e., in the form of virtual objects that dynamically change their shape typically according to variations in heart rate. The goal of this technique is to help patients gaining greater awareness about their bodily reactions and learn how to modify them voluntarily. In fact, changes in physiological signals such as heart rate, respiration, blood pressure, electromyogram, electroencephalogram, and electrodermal response have been related to specific emotional states [24]–[26]. For example, decreases in heart rate variability have been associated with fear, joy, and sadness [25], and higher skin conductance with negative anticipation and stress [27]. Hence, real-time analysis of physiological signals could be used to infer the emotional states experienced during VR interaction and to adapt the elements of the virtual scene in accordance [28]–[31]. In some applications, the biofeedback component has been combined with gaming features to enhance the patient's motivation in performing the task [14], [15], [17]. The body of research on VR and game-based applications for Andrea Gaggioli is with the Department of Psychology, Università Cattolica del Sacro Cuore, and with the Applied Technology for Neuro-Psychology Lab, I.R.C.C.S. Istituto Auxologico Italiano, Milan, Italy (e-mail: andrea.gaggioli@unicatt.it). Stefano Triberti is with the Department of Oncology and Hemato-Oncology, University of Milan, Milan, Italy (e-mail: stefano.triberti@unimi.it). Pietro Cipresso is with the Department of Psychology, Università Cattolica del Sacro Cuore, and with the Applied Technology for Neuro-Psychology Lab, I.R.C.C.S. Istituto Auxologico Italiano, Milan, Italy (e-mail: pietro.cipresso@unicatt.it). Alice Chirico is with the Department of Psychology, Università Cattolica del Sacro Cuore, Milan, Italy (e-mail: alice.chirico@unicatt.it). Sergi Bermúdez i Badia, Luis Velez Quintero, Mónica S Cameirão, Alice Chirico, Stefano Triberti, Pietro Cipresso, and Andrea Gaggioli Towards Emotionally-Adaptive Virtual Reality for Mental Health Applications D