Using Portable EEG Devices to Evaluate Emotional Regulation Strategies during Virtual Reality Exposure

[EN] As Virtual Reality (VR) is starting to be used to train emotional regulation strategies, it would be interesting to propose objective techniques to monitor the emotional reactions of participants during the virtual experience. In this work, the main goal is to analyze if portable EEG systems are adequate to monitor brain activity changes caused by the emotional regulation strategies applied by the participants. The EEG signals captured from subjects that navigate through a virtual environment designed to induce a negative mood will be compared between three experimental groups that will receive different instructions about the emotional regulation strategies to apply. The study will allow us to validate the possibilities of portable EEG devices to monitor emotional regulation strategies during VR exposure.This study was funded by Vicerrectorado de Investigación de la Universitat Politècnica de València, Spain, PAID-06-2011, R.N. 1984; by Ministerio de Educación y Ciencia, Spain, Project Game Teen (TIN2010-20187) and partially by projects Consolider-C (SEJ2006-14301/PSIC), “CIBER of Physiopathology of Obesity and Nutrition, an initiative of ISCIII” and Excellence Research Program PROMETEO (Generalitat Valenciana. Consellería de Educación, 2008-157). The work of A. Rodríguez was supported by the Spanish MEC under an FPI Grant BES-2011-043316.Rey, B.; Rodríguez Ortega, A.; Alcañiz Raya, ML. (2012). Using Portable EEG Devices to Evaluate Emotional Regulation Strategies during Virtual Reality Exposure. Studies in Health Technology and Informatics. 181:223-227. https://doi.org/10.3233/978-1-61499-121-2-223S22322718

Assessing brain activations associated with emotional regulation during virtual reality mood induction procedures

Emotional regulation strategies are used by people to influence their emotional responses to external or internal emotional stimuli. The aim of this study is to evaluate the brain activations that are associated with the application of two different emotional regulation strategies (cognitive reappraisal and expressive suppression) during virtual reality mood induction procedures. We used Emotiv EPOC to measure the brain electrical activity of participants while sadness is induced using a virtual reality environment. We monitored 24 participants, who were distributed among three experimental groups: a control group, a cognitive reappraisal group and an expressive suppression group. In the control group, we found significant activations in several right frontal regions that are related to the induction of negative emotions . We also found significant activations in the limbic, occipital, and parietal regions in the emotional regulation groups. These regions are related to the application of emotional regulation strategies. The results are consistent with those shown in the literature, which were obtained through clinical neuroimaging systems.The work of A. Rodriguez was funded by the Spanish MEC under an FPI Grant BES-2011-043316. The work of Miriam Clemente was funded by the Generalitat Valenciana under a VALi+d Grant.Rodríguez Ortega, A.; Rey, B.; Clemente Bellido, M.; Wrzesien, M.; Alcañiz Raya, ML. (2015). Assessing brain activations associated with emotional regulation during virtual reality mood induction procedures. Expert Systems with Applications. 42(3):1699-1709. https://doi.org/10.1016/j.eswa.2014.10.006S1699170942

Evaluating Virtual Reality Mood Induction Procedures with Portable EEG Devices

[EN] Virtual Environments (VEs) have been used as mood induction procedures. In this context, it is necessary to have instruments to analyze the emotional state during VE exposure. Objective techniques such as EEG should be evaluated for this purpose. The aim in this work was to study the changes in the brain activity with a portable EEG device during a negative mood induction based on a VE. A virtual park was used to induce a negative mood (sadness) in ten participants. Changes in the brain activity of subjects were compared between two moments (before and after emotional induction). Obtained results were in accordance with previous scientific literature regarding frontal EEG asymmetry, which supports the possibility of using the portable EEG as a reliable instrument to measure emotions in VE.This study was funded by Vicerrectorado de Investigación de la Universitat Politècnica de València, Spain, PAID-06-2011, R.N. 1984; by Ministerio de Educación y Ciencia, Spain, Project Game Teen (TIN2010-20187) and partially by projects Consolider-C (SEJ2006-14301/PSIC), “CIBER of Physiopathology of Obesity and Nutrition, an initiative of ISCIII” and Excellence Research Program PROMETEO (Generalitat Valenciana. Consellería de Educación, 2008-157). The work of Alejandro Rodríguez was supported by the Spanish MEC under an FPI Grant BES-2011-043316.Rodríguez Ortega, A.; Rey Solaz, B.; Alcañiz Raya, ML. (2013). Evaluating Virtual Reality Mood Induction Procedures with Portable EEG Devices. Annual Review of Cybertherapy and Telemedicine. 11:131-135. http://hdl.handle.net/10251/78725S1311351

Aportaciones de las nuevas tecnologías combinadas con monitorización fisiológica en el campo de la regulación emocional

Tesis por compendio[EN] Emotional regulation strategies determine the way in which people feel, express and regulate their emotions. These regulation strategies affect all aspects of life. Currently, numerous scientific studies indicate the role that these regulation strategies play in the development and maintenance of adaptive and healthy behavior. On the other hand, deficiencies or deficits in emotional regulation are considered to be relevant factors in the origin and maintenance of numerous behavioral and emotional disorders. There are different instruments that have been traditionally used to train and evaluate emotional regulation capabilities. They are usually based on subjective questionnaires. Although these questionnaires have proven to be useful, they present some limitations that make them little suitable for certain groups who are especially reluctant to be assessed, such as adolescents. Currently, new systems based on man-machine interfaces, such as virtual reality and physiological sensors, are starting to be used for training emotional regulation strategies. The purpose of the research reported in this thesis is to address the issues related to the instruments used to train and evaluate the emotional regulation strategies. Specifically, the aim of this work is to study the combined use of virtual reality and serious games with non-invasive physiological monitoring in the emotional regulation field in adolescent population. For this reason, this document shows the results obtained from three studies, with three different virtual environments where participant were able to train different emotional regulation strategies while their cardiac signal or brain activation were recorded. The aim of this thesis is to make a contribution to the emotional regulation field providing a new research framework through the use of new technologies, such as virtual reality, and through more objective assessment instruments such as physiological signals.[ES] Las estrategias de regulación emocional determinan la forma en que las personas sienten, expresan y regulan sus emociones. Estas estrategias influyen prácticamente en todos los aspectos de la vida. En la actualidad existen numerosas investigaciones que destacan el papel que juegan estas estrategias de regulación emocional en el desarrollo y el mantenimiento de una conducta sana y adaptativa. Por el contrario, carencias o déficits en dichas estrategias de regulación pueden ser consideradas como un factor relevante en el origen y mantenimiento de numerosos trastornos emocionales y de comportamiento. Existen diversos instrumentos que se han utilizado tradicionalmente para evaluar las capacidades de regulación emocional y que están basados en cuestionarios subjetivos. Estos cuestionarios, aunque son muy útiles y prácticos, presentan algunas limitaciones que los hacen poco apropiados, sobre todo para ciertos colectivos que son especialmente reacios a ser evaluados, como podrían ser los adolescentes. Actualmente están empezando a usarse nuevos sistemas basados en tecnologías hombre-máquina, como pueden ser la realidad virtual y los sensores fisiológicos, para el entrenamiento de las estrategias de regulación emocional. La investigación presentada en esta tesis tiene como propósito abordar los aspectos relacionados con los instrumentos utilizados en el entrenamiento y en la evaluación de las estrategias de regulación emocional. Concretamente, el objetivo del presente trabajo es estudiar el uso combinado de la realidad virtual y los juegos serios con la monitorización fisiológica no invasiva en el campo de la regulación emocional en población adolescente. Para ello se presentan y se detallan los resultados obtenidos de tres estudios realizados, con tres entornos virtuales diferentes, donde los participantes pudieron entrenar diferentes estrategias de regulación emocional mientras se les registraban la señal cardíaca o la activación cerebral. Con la presente Tesis Doctoral se pretende hacer una contribución al campo de la regulación emocional, proporcionando un nuevo marco de investigación a través del uso de nuevas tecnologías como la realidad virtual y a través de instrumentos de evaluación más objetivos, como son las señales fisiológicas.[CA] Les estratègies de regulació emocional determinen la manera en què les persones senten, expressen i regulen les seves emocions. Aquestes estratègies influeixen pràcticament en tots els aspectes de la vida. En l'actualitat existeixen nombroses recerques que destaquen el paper que juguen aquestes estratègies de regulació emocional en el desenvolupament i el manteniment d'una conducta sana i adaptativa. Per contra, mancances o dèficits en aquestes estratègies de regulació poden ser considerats com un factor rellevant en l'origen i manteniment de nombrosos trastorns emocionals i de comportament. Existeixen diversos instruments que s'han utilitzat tradicionalment per avaluar les capacitats de regulació emocional i que estan basats en qüestionaris subjectius. Aquests qüestionaris, encara que són molt útils i pràctics, presenten algunes limitacions que els fan poc apropiats, sobretot per a certs col¿lectius que són especialment poc inclinats a ser avaluats, com podrien ser els adolescents. Actualment, estan començant a usar-se nous sistemes basats en tecnologies home-màquina, com pot ser la realitat virtual i els sensors fisiològics, per a l'entrenament de les estratègies de regulació emocional. La investigació presentada en aquesta tesi té com a propòsit abordar els aspectes relacionats amb els instruments utilitzats en l'entrenament i en l'avaluació de les estratègies de regulació emocional. Concretament, l'objectiu del present treball és estudiar l'ús combinat de la realitat virtual i els jocs seriosos amb el monitoratge fisiològic no invasiu en el camp de la regulació emocional en població adolescent. Per a això, es presenten i es detallen els resultats obtinguts de tres estudis realitzats, amb tres entorns virtuals diferents, on els participants van poder entrenar diferents estratègies de regulació emocional mentre se'ls registraven el senyal cardíac o l'activació cerebral. Amb la present Tesi Doctoral es pretén fer una contribució al camp de la regulació emocional, proporcionant un nou marc de investigació a través de l'ús de noves tecnologies com la realitat virtual i a través d'instruments d'avaluació més objectius, com són els senyals fisiològics.Rodríguez Ortega, A. (2015). Aportaciones de las nuevas tecnologías combinadas con monitorización fisiológica en el campo de la regulación emocional [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/51588TESISCompendi

How the physical similarity of avatars can influence the learning of emotion regulation strategies in teenagers

The aim of this study is to evaluate the influence of the physical similarity of avatars with the user on emotion regulation strategy training. In this study twenty-four teenagers observed an avatar (either physically similar to the participant or neutral) that gets frustrated with his/her computer, after which he/she applies an emotion regulation strategy (slow breathing). The intensity of the emotional induction and regulation processes was measured using questionnaires and electroencephalogram data. The results show that observing an avatar that is physically similar to the participant has a significantly greater impact on emotional valence and arousal in participants and also induces emotional states that are significantly more intense than when observing a neutral avatar. The results seem to indicate significantly greater activation of specific brain regions that are related to these processes and greater identification with the avatar in terms of both subjective and objective measures in participants that observed an avatar that was physically similar to them. However, there were no significant differences in the sense of presence or the appeal (i.e., satisfaction) to participants regarding the virtual environment. The use of avatars in mental health applications is relatively new and its specific influence is still unknown. We consider this study to be a first step forward in better understanding the use of avatars in mental health applications for youth. This research brings new guidelines to the design of different types of applications in this field in order to achieve greater behavioral changes in youth.Wrzesien, M.; Rodriguez Ortega, A.; Rey, B.; Alcañiz Raya, ML.; Banos, R.; Vara, M. (2015). How the physical similarity of avatars can influence the learning of emotion regulation strategies in teenagers. Computers in Human Behavior. 43:101-111. doi:10.1016/j.chb.2014.09.024S1011114

Assessment of the influence of navigation control and screen size on the sense of presence in virtual reality using EEG

[EN] In the virtual reality field, presence refers to the sense of being there in the virtual world. Our aim in this work is to evaluate the usefulness of the Emotiv EPOC EEG device to measure brain activations due to the sense of presence in a virtual environment (VE), using for the analysis the sLORETA tool. We compare between three experimental conditions: photographs, video and free navigation through a VE. We also compare the differences in the sense of presence due to the visualization of the VE in different screens: a common desktop screen and a high-resolution power wall screen. We monitored 20 healthy subjects, obtaining significant differences between the navigation and video conditions in the activity of the right Insula for the Theta band. We also found a higher activation of the Insula for the Alpha and Theta bands while navigating, when comparing the two screen types. The Insula activation is related to stimulus attention and self-awareness processes, directly related with the sense of presence.This study was funded by Vicerrectorado de Investigacion de la Universitat Politecnica de Valencia, Spain, PAID-06-2011, R.N. 1984; by Ministerio de Educacion y Ciencia Spain, Project Game Teen (TIN2010-20187) and partially by projects Consolider-C (SEJ2006-14301/PSIC), "CIBER of Physiopathology of Obesity and Nutrition, an initiative of ISCIII", the Excellence Research Program PROMETEO (Generalitat Valenciana. Conselleria de Educacion, 2008-157) and the Consolider INGENIO program (CSD2007-00012). The work of Miriam Clemente was supported by the Generalitat Valenciana under a VALi+d Grant. The work of Alejandro Rodriguez was supported by the Spanish MEC under an FPI Grant BES-2011-043316.Clemente Bellido, M.; Rodríguez Ortega, A.; Rey, B.; Alcañiz Raya, ML. (2014). Assessment of the influence of navigation control and screen size on the sense of presence in virtual reality using EEG. Expert Systems with Applications. 41(4):1584-1592. https://doi.org/10.1016/j.eswa.2013.08.055S1584159241

Adaptive Model for Biofeedback Data Flows Management in the Design of Interactive Immersive Environments

[Abstract] The interactivity of an immersive environment comes up from the relationship that is established between the user and the system. This relationship results in a set of data exchanges between human and technological actors. The real-time biofeedback devices allow to collect in real time the biodata generated by the user during the exhibition. The analysis, processing and conversion of these biodata into multimodal data allows to relate the stimuli with the emotions they trigger. This work describes an adaptive model for biofeedback data flows management used in the design of interactive immersive systems. The use of an affective algorithm allows to identify the types of emotions felt by the user and the respective intensities. The mapping between stimuli and emotions creates a set of biodata that can be used as elements of interaction that will readjust the stimuli generated by the system. The real-time interaction generated by the evolution of the user’s emotional state and the stimuli generated by the system allows him to adapt attitudes and behaviors to the situations he faces

Modelling human emotions using immersive virtual reality, physiological signals and behavioural responses

Tesis por compendio[ES] El uso de la realidad virtual (RV) se ha incrementado notablemente en la comunidad científica para la investigación del comportamiento humano. En particular, la RV inmersiva ha crecido debido a la democratización de las gafas de realidad virtual o head mounted displays (HMD), que ofrecen un alto rendimiento con una inversión económica. Uno de los campos que ha emergido con fuerza en la última década es el Affective Computing, que combina psicofisiología, informática, ingeniería biomédica e inteligencia artificial, desarrollando sistemas que puedan reconocer emociones automáticamente. Su progreso es especialmente importante en el campo de la investigación del comportamiento humano, debido al papel fundamental que las emociones juegan en muchos procesos psicológicos como la percepción, la toma de decisiones, la creatividad, la memoria y la interacción social. Muchos estudios se han centrado en intentar obtener una metodología fiable para evocar y automáticamente identificar estados emocionales, usando medidas fisiológicas objetivas y métodos de aprendizaje automático. Sin embargo, la mayoría de los estudios previos utilizan imágenes, audios o vídeos para generar los estados emocionales y, hasta donde llega nuestro conocimiento, ninguno de ellos ha desarrollado un sistema de reconocimiento emocional usando RV inmersiva. Aunque algunos trabajos anteriores sí analizan las respuestas fisiológicas en RV inmersivas, estos no presentan modelos de aprendizaje automático para procesamiento y clasificación automática de bioseñales. Además, un concepto crucial cuando se usa la RV en investigación del comportamiento humano es la validez: la capacidad de evocar respuestas similares en un entorno virtual a las evocadas por el espacio físico. Aunque algunos estudios previos han usado dimensiones psicológicas y cognitivas para comparar respuestas entre entornos reales y virtuales, las investigaciones que analizan respuestas fisiológicas o comportamentales están mucho menos extendidas. Según nuestros conocimientos, este es el primer trabajo que compara entornos físicos con su réplica en RV, empleando respuestas fisiológicas y algoritmos de aprendizaje automático y analizando la capacidad de la RV de transferir y extrapolar las conclusiones obtenidas al entorno real que se está simulando. El objetivo principal de la tesis es validar el uso de la RV inmersiva como una herramienta de estimulación emocional usando respuestas psicofisiológicas y comportamentales en combinación con algoritmos de aprendizaje automático, así como realizar una comparación directa entre un entorno real y virtual. Para ello, se ha desarrollado un protocolo experimental que incluye entornos emocionales 360º, un museo real y una virtualización 3D altamente realista del mismo museo. La tesis presenta novedosas contribuciones del uso de la RV inmersiva en la investigación del comportamiento humano, en particular en lo relativo al estudio de las emociones. Esta ayudará a aplicar metodologías a estímulos más realistas para evaluar entornos y situaciones de la vida diaria, superando las actuales limitaciones de la estimulación emocional que clásicamente ha incluido imágenes, audios o vídeos. Además, en ella se analiza la validez de la RV realizando una comparación directa usando una simulación altamente realista. Creemos que la RV inmersiva va a revolucionar los métodos de estimulación emocional en entornos de laboratorio. Además, su sinergia junto a las medidas fisiológicas y las técnicas de aprendizaje automático, impactarán transversalmente en muchas áreas de investigación como la arquitectura, la salud, la evaluación psicológica, el entrenamiento, la educación, la conducción o el marketing, abriendo un nuevo horizonte de oportunidades para la comunidad científica. La presente tesis espera contribuir a caminar en esa senda.[EN] In recent years the scientific community has significantly increased its use of virtual reality (VR) technologies in human behaviour research. In particular, the use of immersive VR has grown due to the introduction of affordable, high performance head mounted displays (HMDs). Among the fields that has strongly emerged in the last decade is affective computing, which combines psychophysiology, computer science, biomedical engineering and artificial intelligence in the development of systems that can automatically recognize emotions. The progress of affective computing is especially important in human behaviour research due to the central role that emotions play in many background processes, such as perception, decision-making, creativity, memory and social interaction. Several studies have tried to develop a reliable methodology to evoke and automatically identify emotional states using objective physiological measures and machine learning methods. However, the majority of previous studies used images, audio or video to elicit emotional statements; to the best of our knowledge, no previous research has developed an emotion recognition system using immersive VR. Although some previous studies analysed physiological responses in immersive VR, they did not use machine learning techniques for biosignal processing and classification. Moreover, a crucial concept when using VR for human behaviour research is validity: the capacity to evoke a response from the user in a simulated environment similar to the response that might be evoked in a physical environment. Although some previous studies have used psychological and cognitive dimensions to compare responses in real and virtual environments, few have extended this research to analyse physiological or behavioural responses. Moreover, to our knowledge, this is the first study to compare VR scenarios with their real-world equivalents using physiological measures coupled with machine learning algorithms, and to analyse the ability of VR to transfer and extrapolate insights obtained from VR environments to real environments. The main objective of this thesis is, using psycho-physiological and behavioural responses in combination with machine learning methods, and by performing a direct comparison between a real and virtual environment, to validate immersive VR as an emotion elicitation tool. To do so we develop an experimental protocol involving emotional 360º environments, an art exhibition in a real museum, and a highly-realistic 3D virtualization of the same art exhibition. This thesis provides novel contributions to the use of immersive VR in human behaviour research, particularly in relation to emotions. VR can help in the application of methodologies designed to present more realistic stimuli in the assessment of daily-life environments and situations, thus overcoming the current limitations of affective elicitation, which classically uses images, audio and video. Moreover, it analyses the validity of VR by performing a direct comparison using highly-realistic simulation. We believe that immersive VR will revolutionize laboratory-based emotion elicitation methods. Moreover, its synergy with physiological measurement and machine learning techniques will impact transversely in many other research areas, such as architecture, health, assessment, training, education, driving and marketing, and thus open new opportunities for the scientific community. The present dissertation aims to contribute to this progress.[CA] L'ús de la realitat virtual (RV) s'ha incrementat notablement en la comunitat científica per a la recerca del comportament humà. En particular, la RV immersiva ha crescut a causa de la democratització de les ulleres de realitat virtual o head mounted displays (HMD), que ofereixen un alt rendiment amb una reduïda inversió econòmica. Un dels camps que ha emergit amb força en l'última dècada és el Affective Computing, que combina psicofisiologia, informàtica, enginyeria biomèdica i intel·ligència artificial, desenvolupant sistemes que puguen reconéixer emocions automàticament. El seu progrés és especialment important en el camp de la recerca del comportament humà, a causa del paper fonamental que les emocions juguen en molts processos psicològics com la percepció, la presa de decisions, la creativitat, la memòria i la interacció social. Molts estudis s'han centrat en intentar obtenir una metodologia fiable per a evocar i automàticament identificar estats emocionals, utilitzant mesures fisiològiques objectives i mètodes d'aprenentatge automàtic. No obstant això, la major part dels estudis previs utilitzen imatges, àudios o vídeos per a generar els estats emocionals i, fins on arriba el nostre coneixement, cap d'ells ha desenvolupat un sistema de reconeixement emocional mitjançant l'ús de la RV immersiva. Encara que alguns treballs anteriors sí que analitzen les respostes fisiològiques en RV immersives, aquests no presenten models d'aprenentatge automàtic per a processament i classificació automàtica de biosenyals. A més, un concepte crucial quan s'utilitza la RV en la recerca del comportament humà és la validesa: la capacitat d'evocar respostes similars en un entorn virtual a les evocades per l'espai físic. Encara que alguns estudis previs han utilitzat dimensions psicològiques i cognitives per a comparar respostes entre entorns reals i virtuals, les recerques que analitzen respostes fisiològiques o comportamentals estan molt menys esteses. Segons els nostres coneixements, aquest és el primer treball que compara entorns físics amb la seua rèplica en RV, emprant respostes fisiològiques i algorismes d'aprenentatge automàtic i analitzant la capacitat de la RV de transferir i extrapolar les conclusions obtingudes a l'entorn real que s'està simulant. L'objectiu principal de la tesi és validar l'ús de la RV immersiva com una eina d'estimulació emocional usant respostes psicofisiològiques i comportamentals en combinació amb algorismes d'aprenentatge automàtic, així com realitzar una comparació directa entre un entorn real i virtual. Per a això, s'ha desenvolupat un protocol experimental que inclou entorns emocionals 360º, un museu real i una virtualització 3D altament realista del mateix museu. La tesi presenta noves contribucions de l'ús de la RV immersiva en la recerca del comportament humà, en particular quant a l'estudi de les emocions. Aquesta ajudarà a aplicar metodologies a estímuls més realistes per a avaluar entorns i situacions de la vida diària, superant les actuals limitacions de l'estimulació emocional que clàssicament ha inclòs imatges, àudios o vídeos. A més, en ella s'analitza la validesa de la RV realitzant una comparació directa usant una simulació altament realista. Creiem que la RV immersiva revolucionarà els mètodes d'estimulació emocional en entorns de laboratori. A més, la seua sinergia al costat de les mesures fisiològiques i les tècniques d'aprenentatge automàtic, impactaran transversalment en moltes àrees de recerca com l'arquitectura, la salut, l'avaluació psicològica, l'entrenament, l'educació, la conducció o el màrqueting, obrint un nou horitzó d'oportunitats per a la comunitat científica. La present tesi espera contribuir a caminar en aquesta senda.Marín Morales, J. (2020). Modelling human emotions using immersive virtual reality, physiological signals and behavioural responses [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/148717TESISCompendi

Serious Games and Mixed Reality Applications for Healthcare

Virtual reality (VR) and augmented reality (AR) have long histories in the healthcare sector, offering the opportunity to develop a wide range of tools and applications aimed at improving the quality of care and efficiency of services for professionals and patients alike. The best-known examples of VR–AR applications in the healthcare domain include surgical planning and medical training by means of simulation technologies. Techniques used in surgical simulation have also been applied to cognitive and motor rehabilitation, pain management, and patient and professional education. Serious games are ones in which the main goal is not entertainment, but a crucial purpose, ranging from the acquisition of knowledge to interactive training.These games are attracting growing attention in healthcare because of their several benefits: motivation, interactivity, adaptation to user competence level, flexibility in time, repeatability, and continuous feedback. Recently, healthcare has also become one of the biggest adopters of mixed reality (MR), which merges real and virtual content to generate novel environments, where physical and digital objects not only coexist, but are also capable of interacting with each other in real time, encompassing both VR and AR applications.This Special Issue aims to gather and publish original scientific contributions exploring opportunities and addressing challenges in both the theoretical and applied aspects of VR–AR and MR applications in healthcare