396 research outputs found

    A Multi-Modal, Modified-Feedback and Self-Paced Brain-Computer Interface (BCI) to Control an Embodied Avatar's Gait

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    Brain-computer interfaces (BCI) have been used to control the gait of a virtual self-avatar with the aim of being used in gait rehabilitation. A BCI decodes the brain signals representing a desire to do something and transforms them into a control command for controlling external devices. The feelings described by the participants when they control a self-avatar in an immersive virtual environment (VE) demonstrate that humans can be embodied in the surrogate body of an avatar (ownership illusion). It has recently been shown that inducing the ownership illusion and then manipulating the movements of one’s self-avatar can lead to compensatory motor control strategies. In order to maximize this effect, there is a need for a method that measures and monitors embodiment levels of participants immersed in virtual reality (VR) to induce and maintain a strong ownership illusion. This is particularly true given that reaching a high level of both BCI performance and embodiment are inter-connected. To reach one of them, the second must be reached as well. Some limitations of many existing systems hinder their adoption for neurorehabilitation: 1- some use motor imagery (MI) of movements other than gait; 2- most systems allow the user to take single steps or to walk but do not allow both, which prevents users from progressing from steps to gait; 3- most of them function in a single BCI mode (cue-paced or self-paced), which prevents users from progressing from machine-dependent to machine-independent walking. Overcoming the aforementioned limitations can be done by combining different control modes and options in one single system. However, this would have a negative impact on BCI performance, therefore diminishing its usefulness as a potential rehabilitation tool. In this case, there will be a need to enhance BCI performance. For such purpose, many techniques have been used in the literature, such as providing modified feedback (whereby the presented feedback is not consistent with the user’s MI), sequential training (recalibrating the classifier as more data becomes available). This thesis was developed over 3 studies. The objective in study 1 was to investigate the possibility of measuring the level of embodiment of an immersive self-avatar, during the performing, observing and imagining of gait, using electroencephalogram (EEG) techniques, by presenting visual feedback that conflicts with the desired movement of embodied participants. The objective of study 2 was to develop and validate a BCI to control single steps and forward walking of an immersive virtual reality (VR) self-avatar, using mental imagery of these actions, in cue-paced and self-paced modes. Different performance enhancement strategies were implemented to increase BCI performance. The data of these two studies were then used in study 3 to construct a generic classifier that could eliminate offline calibration for future users and shorten training time. Twenty different healthy participants took part in studies 1 and 2. In study 1, participants wore an EEG cap and motion capture markers, with an avatar displayed in a head-mounted display (HMD) from a first-person perspective (1PP). They were cued to either perform, watch or imagine a single step forward or to initiate walking on a treadmill. For some of the trials, the avatar took a step with the contralateral limb or stopped walking before the participant stopped (modified feedback). In study 2, participants completed a 4-day sequential training to control the gait of an avatar in both BCI modes. In cue-paced mode, they were cued to imagine a single step forward, using their right or left foot, or to walk forward. In the self-paced mode, they were instructed to reach a target using the MI of multiple steps (switch control mode) or maintaining the MI of forward walking (continuous control mode). The avatar moved as a response to two calibrated regularized linear discriminant analysis (RLDA) classifiers that used the μ power spectral density (PSD) over the foot area of the motor cortex as features. The classifiers were retrained after every session. During the training, and for some of the trials, positive modified feedback was presented to half of the participants, where the avatar moved correctly regardless of the participant’s real performance. In both studies, the participants’ subjective experience was analyzed using a questionnaire. Results of study 1 show that subjective levels of embodiment correlate strongly with the power differences of the event-related synchronization (ERS) within the μ frequency band, and over the motor and pre-motor cortices between the modified and regular feedback trials. Results of study 2 show that all participants were able to operate the cued-paced BCI and the selfpaced BCI in both modes. For the cue-paced BCI, the average offline performance (classification rate) on day 1 was 67±6.1% and 86±6.1% on day 3, showing that the recalibration of the classifiers enhanced the offline performance of the BCI (p < 0.01). The average online performance was 85.9±8.4% for the modified feedback group (77-97%) versus 75% for the non-modified feedback group. For self-paced BCI, the average performance was 83% at switch control and 92% at continuous control mode, with a maximum of 12 seconds of control. Modified feedback enhanced BCI performances (p =0.001). Finally, results of study 3 show that the constructed generic models performed as well as models obtained from participant-specific offline data. The results show that there it is possible to design a participant-independent zero-training BCI.Les interfaces cerveau-ordinateur (ICO) ont été utilisées pour contrôler la marche d'un égo-avatar virtuel dans le but d'être utilisées dans la réadaptation de la marche. Une ICO décode les signaux du cerveau représentant un désir de faire produire un mouvement et les transforme en une commande de contrôle pour contrôler des appareils externes. Les sentiments décrits par les participants lorsqu'ils contrôlent un égo-avatar dans un environnement virtuel immersif démontrent que les humains peuvent être incarnés dans un corps d'un avatar (illusion de propriété). Il a été récemment démontré que provoquer l’illusion de propriété puis manipuler les mouvements de l’égo-avatar peut conduire à des stratégies de contrôle moteur compensatoire. Afin de maximiser cet effet, il existe un besoin d'une méthode qui mesure et surveille les niveaux d’incarnation des participants immergés dans la réalité virtuelle (RV) pour induire et maintenir une forte illusion de propriété. D'autre part, atteindre un niveau élevé de performances (taux de classification) ICO et d’incarnation est interconnecté. Pour atteindre l'un d'eux, le second doit également être atteint. Certaines limitations de plusieurs de ces systèmes entravent leur adoption pour la neuroréhabilitation: 1- certains utilisent l'imagerie motrice (IM) des mouvements autres que la marche; 2- la plupart des systèmes permettent à l'utilisateur de faire des pas simples ou de marcher mais pas les deux, ce qui ne permet pas à un utilisateur de passer des pas à la marche; 3- la plupart fonctionnent en un seul mode d’ICO, rythmé (cue-paced) ou auto-rythmé (self-paced). Surmonter les limitations susmentionnées peut être fait en combinant différents modes et options de commande dans un seul système. Cependant, cela aurait un impact négatif sur les performances de l’ICO, diminuant ainsi son utilité en tant qu'outil potentiel de réhabilitation. Dans ce cas, il sera nécessaire d'améliorer les performances des ICO. À cette fin, de nombreuses techniques ont été utilisées dans la littérature, telles que la rétroaction modifiée, le recalibrage du classificateur et l'utilisation d'un classificateur générique. Le projet de cette thèse a été réalisé en 3 études, avec objectif d'étudier dans l'étude 1, la possibilité de mesurer le niveau d'incarnation d'un égo-avatar immersif, lors de l'exécution, de l'observation et de l'imagination de la marche, à l'aide des techniques encéphalogramme (EEG), en présentant une rétroaction visuelle qui entre en conflit avec la commande du contrôle moteur des sujets incarnés. L'objectif de l'étude 2 était de développer un BCI pour contrôler les pas et la marche vers l’avant d'un égo-avatar dans la réalité virtuelle immersive, en utilisant l'imagerie motrice de ces actions, dans des modes rythmés et auto-rythmés. Différentes stratégies d'amélioration des performances ont été mises en œuvre pour augmenter la performance (taux de classification) de l’ICO. Les données de ces deux études ont ensuite été utilisées dans l'étude 3 pour construire des classificateurs génériques qui pourraient éliminer la calibration hors ligne pour les futurs utilisateurs et raccourcir le temps de formation. Vingt participants sains différents ont participé aux études 1 et 2. Dans l'étude 1, les participants portaient un casque EEG et des marqueurs de capture de mouvement, avec un avatar affiché dans un casque de RV du point de vue de la première personne (1PP). Ils ont été invités à performer, à regarder ou à imaginer un seul pas en avant ou la marche vers l’avant (pour quelques secondes) sur le tapis roulant. Pour certains essais, l'avatar a fait un pas avec le membre controlatéral ou a arrêté de marcher avant que le participant ne s'arrête (rétroaction modifiée). Dans l'étude 2, les participants ont participé à un entrainement séquentiel de 4 jours pour contrôler la marche d'un avatar dans les deux modes de l’ICO. En mode rythmé, ils ont imaginé un seul pas en avant, en utilisant leur pied droit ou gauche, ou la marche vers l’avant . En mode auto-rythmé, il leur a été demandé d'atteindre une cible en utilisant l'imagerie motrice (IM) de plusieurs pas (mode de contrôle intermittent) ou en maintenir l'IM de marche vers l’avant (mode de contrôle continu). L'avatar s'est déplacé en réponse à deux classificateurs ‘Regularized Linear Discriminant Analysis’ (RLDA) calibrés qui utilisaient comme caractéristiques la densité spectrale de puissance (Power Spectral Density; PSD) des bandes de fréquences µ (8-12 Hz) sur la zone du pied du cortex moteur. Les classificateurs ont été recalibrés après chaque session. Au cours de l’entrainement et pour certains des essais, une rétroaction modifiée positive a été présentée à la moitié des participants, où l'avatar s'est déplacé correctement quelle que soit la performance réelle du participant. Dans les deux études, l'expérience subjective des participants a été analysée à l'aide d'un questionnaire. Les résultats de l'étude 1 montrent que les niveaux subjectifs d’incarnation sont fortement corrélés à la différence de la puissance de la synchronisation liée à l’événement (Event-Related Synchronization; ERS) sur la bande de fréquence μ et sur le cortex moteur et prémoteur entre les essais de rétroaction modifiés et réguliers. L'étude 2 a montré que tous les participants étaient capables d’utiliser le BCI rythmé et auto-rythmé dans les deux modes. Pour le BCI rythmé, la performance hors ligne moyenne au jour 1 était de 67±6,1% et 86±6,1% au jour 3, ce qui montre que le recalibrage des classificateurs a amélioré la performance hors ligne du BCI (p <0,01). La performance en ligne moyenne était de 85,9±8,4% pour le groupe de rétroaction modifié (77-97%) contre 75% pour le groupe de rétroaction non modifié. Pour le BCI auto-rythmé, la performance moyenne était de 83% en commande de commutateur et de 92% en mode de commande continue, avec un maximum de 12 secondes de commande. Les performances de l’ICO ont été améliorées par la rétroaction modifiée (p = 0,001). Enfin, les résultats de l'étude 3 montrent que pour la classification des initialisations des pas et de la marche, il a été possible de construire des modèles génériques à partir de données hors ligne spécifiques aux participants. Les résultats montrent la possibilité de concevoir une ICO ne nécessitant aucun entraînement spécifique au participant

    ”Mine works better” - Examining the influence of embodiment in virtual reality on the sense of agency during a binary motor imagery task with a brain-computer interface

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    Motor imagery-based brain-computer interfaces (MI-BCI) have been proposed as a means for stroke rehabilitation, which combined with virtual reality allows for introducing game-based interactions into rehabilitation. However, the control of the MI-BCI may be difficult to obtain and users may face poor performance which frustrates them and potentially affects their motivation to use the technology. Decreases in motivation could be reduced by increasing the users' sense of agency over the system. The aim of this study was to understand whether embodiment (ownership) of a hand depicted in virtual reality can enhance the sense of agency to reduce frustration in an MI-BCI task. Twenty-two healthy participants participated in a within-subject study where their sense of agency was compared in two different embodiment experiences: 1) avatar hand (with body), or 2) abstract blocks. Both representations closed with a similar motion for spatial congruency and popped a balloon as a result. The hand/blocks were controlled through an online MI-BCI. Each condition consisted of 30 trials of MI-activation of the avatar hand/blocks. After each condition a questionnaire probed the participants' sense of agency, ownership, and frustration. Afterwards, a semi-structured interview was performed where the participants elaborated on their ratings. Both conditions supported similar levels of MI-BCI performance. A significant correlation between ownership and agency was observed (r = 0.47, p = 0.001). As intended, the avatar hand yielded much higher ownership than the blocks. When controlling for performance, ownership increased sense of agency. In conclusion, designers of BCI-based rehabilitation applications can draw on anthropomorphic avatars for the visual mapping of the trained limb to improve ownership. While not While not reducing frustration ownership can improve perceived agency given sufficient BCI performance. In future studies the findings should be validated in stroke patients since they may perceive agency and ownership differently than able-bodied users

    The sense of embodiment in Virtual Reality and its assessment methods

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    The sense of embodiment refers to the sensations of being inside, having, and controlling a body. In virtual reality, it is possible to substitute a person’s body with a virtual body, referred to as an avatar. Modulations of the sense of embodiment through modifications of this avatar have perceptual and behavioural consequences on users that can influence the way users interact with the virtual environment. Therefore, it is essential to define metrics that enable a reliable assessment of the sense of embodiment in virtual reality to better understand its dimensions, the way they interact, and their influence on the quality of interaction in the virtual environment. In this review, we first introduce the current knowledge on the sense of embodiment, its dimensions (senses of agency, body ownership, and self-location), and how they relate the ones with the others. Then, we dive into the different methods currently used to assess the sense of embodiment, ranging from questionnaires to neurophysiological measures. We provide a critical analysis of the existing metrics, discussing their advantages and drawbacks in the context of virtual reality. Notably, we argue that real-time measures of embodiment, which are also specific and do not require double tasking, are the most relevant in the context of virtual reality. Electroencephalography seems a good candidate for the future if its drawbacks (such as its sensitivity to movement and practicality) are improved. While the perfect metric has yet to be identified if it exists, this work provides clues on which metric to choose depending on the context, which should hopefully contribute to better assessing and understanding the sense of embodiment in virtual reality

    Neurophysiological signatures of the body representation in the brain using Immersive Virtual Reality

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    [spa] Múltiples estudios han demostrado que es posible sustituir el cuerpo de una persona por uno virtual produciendo ilusiones de posesión y agencia sobre este nuevo cuerpo. Los efectos y trazas de esta sustitución de cuerpos se pueden medir de manera subjetiva, a través del comportamiento del participante o a través de medidas fisiológicas objetivas. Sin embargo, restan por descubrir muchos de los mecanismos neurológicos subyacentes que provocan dichos efectos. Esta tesis pretende medir correlaciones neurofisiológicas de las ilusiones de posesión y agencia, y de esta manera contribuir al mayor conocimiento del funcionamiento de la representación corporal en el cerebro. Para ello realizamos una serie de estudios donde la representación del cuerpo humano y su actividad son externamente manipuladas de diversas maneras mediante estimulación multisensorial mientras se registra la correspondiente actividad cerebral mediante electroencefalografía (EEG). La estimulación multisensorial permite que humanos sanos puedan tener ilusiones de posesión y agencia sobre avatares (como si sus cuerpos hubieran sido perceptualmente sustituidos por cuerpos virtuales). Más en concreto, mediante el uso de Realidad Virtual (RV) los participantes tienen una perspectiva egocéntrica de un cuerpo yuxtapuesto al suyo (a través de cascos de realidad virtual estereoscópicos). A la vez que pueden mover este cuerpo mediante sistemas de rastreo del movimiento en tiempo real produciendo una estimulación visuo-motora síncrona. La combinación de la perspectiva en primera persona con la estimulación visuo-motora da como resultado una ilusión de posesión y control total del cuerpo virtual, a la que nos referimos como encarnación virtual. En este escenario exploramos las implicaciones de estas manipulaciones perceptuales en el cerebro mediante EEG. Planteamos un primer experimento con intención de validar si el cuerpo virtual se puede efectivamente reconocer como un sustituto viable del propio cuerpo a nivel del subconsciente. Tras exponer el cuerpo virtual a estímulos nocivos se halla una activación en la corteza motora de los participantes equivalente a la que sería de esperar en un escenario real. Este resultado-como-real hace indicar que los participantes ciertamente aceptan sus cuerpos virtuales dados como su propio cuerpo. En un segundo experimento se estudian las consecuencias de los mecanismos de agencia que nos proporcionan la consciencia de nuestras acciones corporales y motoras, a través de tecnologías de substitución virtual del cuerpo. Los participantes se someten a disrupciones esporádicas de sus acciones mientras realizan movimientos rápidos con su brazo. En algunas ocasiones, la mano virtual del participante se mueve autónomamente y en dirección contraria a la mano real del participante. Los resultados proporcionan evidencias de procesos neuronales específicos responsables de detectar disrupciones de agencia inducidas externamente. Asimismo, estos procesos neuronales se correlacionan con la ilusión de posesión del cuerpo medida a través de cuestionarios. Este estudio profundiza en las perspectivas actuales de los esquemas de agencia, proponiendo y demostrando la teoría existente de mecanismos de errores re-aferentes y de retro-alimentación que funcionan concurrentemente en el cerebro para detectar disrupciones de agencia. Se propone un tercer experimento para explorar las implicaciones de la apariencia externa del cuerpo virtual a la hora de auto-reconocerse. Diseñamos un experimento en el que los participantes se exponen a caras de avatares que se parecen a ellos, a un familiar o a una persona que no conocen. Los resultados muestran mecanismos subyacentes compartidos de auto-identificación de caras reales y virtuales en la corteza visual. En particular, las trazas neurofisiológicas muestran que las caras virtuales se clasifican igual que las reales (en contraste con lo que ocurre durante la clasificación de otros objetos como coches o flores). Además, la corteza visual diferencia niveles de familiaridad entre las caras virtuales. Contribuyendo así de manera novedosa a entender porque avatares con diferente apariencia tienen un impacto en el comportamiento de los participantes, y por ello siendo útil tanto para el campo de la realidad virtual como para el de la auto-identificación. Globalmente, la investigación de esta tesis explora las trazas cerebrales mediante EEG de la experiencia inmediata de poseer y controlar un cuerpo. Se presentan evidencias empíricas para validar el uso de realidad virtual en la investigación de la representación del cuerpo en el cerebro. Asimismo, a través de varios estudios mostramos novedosas trazas neurofisiológicas relacionadas con las manipulaciones corporales y perceptuales. Los resultados y experimentos se contextualizan mediante una revisión en profundidad de la literatura existente en consciencia, percepción corporal y teorías de posesión y agencia del propio cuerpo.[eng] Several studies have shown that it is possible to substitute a person’s body by a virtual one giving rise to illusions of ownership and agency with respect to the virtual body. The effects and traces of such body substitution can be measured using subjective reporting, behavioural and objective physiological measures. However, considerable work remains for uncovering the underlying neurological mechanisms that trigger those effects. In this thesis we aim to measure neurophysiological correlates of ownership and agency, and by doing so to contribute to a greater understanding of the functioning of the body representation in the brain. In order to address this question we carried out a series of studies where the representation of the human body and activity in which it was engaged were externally manipulated in various ways through multisensory stimulation, while measuring the corresponding electroencephalography (EEG) responses. Through this multisensory stimulation, healthy humans experienced full body ownership and agency illusions over virtual bodies – as if their real bodies were perceptually substituted by these bodies. Specifically, Virtual Reality (VR) was used to give participants an egocentric view of a co-located virtual body, using a Head-Mounted Display. They could move this body through real-time motion tracking thus providing synchronous visuo-motor stimulation. The combination of the first person perspective and synchronous visuo-motor stimulation resulted in full body ownership and agency illusions over the virtual body, which we refer to as virtual embodiment. Under these circumstances we then explored the implications of such bodily perceptual manipulations in the brain with EEG. A first study was intended to validate whether a virtual body can be effectively recognized as a feasible substitute to the self-body at the unconscious level. A motor cortex activation equivalent to what would be expected in a real scenario was found after exposing participants’ virtual body to harmful stimuli. This particular result provides a measure of response-as-if-real indicating that participants tended to accept their given virtual bodies as their own. In a second study, the consequences of the agency mechanisms that provide the sensation of control over our own body actions were explored through virtual embodiment. In this study participants underwent sporadic agency disruptions while performing rapid arm movements. In certain conditions, the virtual hand of participants moved autonomously in the opposite direction to the participants’ real hand. Results provide evidence of specific neural processes responsible for detecting externally induced agency disruptions. Moreover, these neural processes were correlated with the strength of the subjective embodiment illusion. This study was also aimed at widening current perspectives on agency schemas, proposing and demonstrating the existing theory of re-afferent and feedback error mechanisms that are concurrently functioning in the brain to detect agency disruptions. In a third study the implications of the external appearance of the substitute virtual body for self-recognition were explored. We designed an experiment in which healthy participants were exposed to self, familiar and unknown faces of look-alike avatars. Results showed shared underlying mechanisms for self-identification in real and virtual faces in the visual cortex. In particular, neurophysiological traces showed that virtual faces are classified as real faces – in contrast to what happens with the classification of other objects (cars, flowers, etc.). Furthermore, the visual cortex differentiated familiarity levels among virtual faces. These are novel insights contributing to the better understanding of why different looking avatars can have an impact on participants’ performance or behaviour, thus being useful both for the fields of virtual embodiment and of self-recognition. Overall the research in this thesis explores brain activity through EEG of the immediate experience of having and controlling a body. Empirical evidence is presented to validate the use of virtual reality for the research of the body representation in the brain. Additionally, novel neural signatures of the bodily perceptual manipulations are presented through a set of studies. Results are put into context with an in-depth review of literature on self-awareness, body perception, body ownership and agency theories at the beginning of this thesis

    Neurophysiological signatures of the body representation in the brain using Immersive Virtual Reality

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    Several studies have shown that it is possible to substitute a person’s body by a virtual one giving rise to illusions of ownership and agency with respect to the virtual body. The effects and traces of such body substitution can be measured using subjective reporting, behavioural and objective physiological measures. However, considerable work remains for uncovering the underlying neurological mechanisms that trigger those effects. In this thesis we aim to measure neurophysiological correlates of ownership and agency, and by doing so to contribute to a greater understanding of the functioning of the body representation in the brain. In order to address this question we carried out a series of studies where the representation of the human body and activity in which it was engaged were externally manipulated in various ways through multisensory stimulation, while measuring the corresponding electroencephalography (EEG) responses. Through this multisensory stimulation, healthy humans experienced full body ownership and agency illusions over virtual bodies – as if their real bodies were perceptually substituted by these bodies. Specifically, Virtual Reality (VR) was used to give participants an egocentric view of a co-located virtual body, using a Head-Mounted Display. They could move this body through real-time motion tracking thus providing synchronous visuo-motor stimulation. The combination of the first person perspective and synchronous visuo-motor stimulation resulted in full body ownership and agency illusions over the virtual body, which we refer to as virtual embodiment. Under these circumstances we then explored the implications of such bodily perceptual manipulations in the brain with EEG. A first study was intended to validate whether a virtual body can be effectively recognized as a feasible substitute to the self-body at the unconscious level. A motor cortex activation equivalent to what would be expected in a real scenario was found after exposing participants’ virtual body to harmful stimuli. This particular result provides a measure of response-as-if-real indicating that participants tended to accept their given virtual bodies as their own. In a second study, the consequences of the agency mechanisms that provide the sensation of control over our own body actions were explored through virtual embodiment. In this study participants underwent sporadic agency disruptions while performing rapid arm movements. In certain conditions, the virtual hand of participants moved autonomously in the opposite direction to the participants’ real hand. Results provide evidence of specific neural processes responsible for detecting externally induced agency disruptions. Moreover, these neural processes were correlated with the strength of the subjective embodiment illusion. This study was also aimed at widening current perspectives on agency schemas, proposing and demonstrating the existing theory of re-afferent and feedback error mechanisms that are concurrently functioning in the brain to detect agency disruptions. In a third study the implications of the external appearance of the substitute virtual body for self-recognition were explored. We designed an experiment in which healthy participants were exposed to self, familiar and unknown faces of look-alike avatars. Results showed shared underlying mechanisms for self-identification in real and virtual faces in the visual cortex. In particular, neurophysiological traces showed that virtual faces are classified as real faces – in contrast to what happens with the classification of other objects (cars, flowers, etc.). Furthermore, the visual cortex differentiated familiarity levels among virtual faces. These are novel insights contributing to the better understanding of why different looking avatars can have an impact on participants’ performance or behaviour, thus being useful both for the fields of virtual embodiment and of self-recognition. Overall the research in this thesis explores brain activity through EEG of the immediate experience of having and controlling a body. Empirical evidence is presented to validate the use of virtual reality for the research of the body representation in the brain. Additionally, novel neural signatures of the bodily perceptual manipulations are presented through a set of studies. Results are put into context with an in-depth review of literature on self-awareness, body perception, body ownership and agency theories at the beginning of this thesis.Múltiples estudios han demostrado que es posible sustituir el cuerpo de una persona por uno virtual produciendo ilusiones de posesión y agencia sobre este nuevo cuerpo. Los efectos y trazas de esta sustitución de cuerpos se pueden medir de manera subjetiva, a través del comportamiento del participante o a través de medidas fisiológicas objetivas. Sin embargo, restan por descubrir muchos de los mecanismos neurológicos subyacentes que provocan dichos efectos. Esta tesis pretende medir correlaciones neurofisiológicas de las ilusiones de posesión y agencia, y de esta manera contribuir al mayor conocimiento del funcionamiento de la representación corporal en el cerebro. Para ello realizamos una serie de estudios donde la representación del cuerpo humano y su actividad son externamente manipuladas de diversas maneras mediante estimulación multisensorial mientras se registra la correspondiente actividad cerebral mediante electroencefalografía (EEG). La estimulación multisensorial permite que humanos sanos puedan tener ilusiones de posesión y agencia sobre avatares (como si sus cuerpos hubieran sido perceptualmente sustituidos por cuerpos virtuales). Más en concreto, mediante el uso de Realidad Virtual (RV) los participantes tienen una perspectiva egocéntrica de un cuerpo yuxtapuesto al suyo (a través de cascos de realidad virtual estereoscópicos). A la vez que pueden mover este cuerpo mediante sistemas de rastreo del movimiento en tiempo real produciendo una estimulación visuo-motora síncrona. La combinación de la perspectiva en primera persona con la estimulación visuo-motora da como resultado una ilusión de posesión y control total del cuerpo virtual, a la que nos referimos como encarnación virtual. En este escenario exploramos las implicaciones de estas manipulaciones perceptuales en el cerebro mediante EEG. Planteamos un primer experimento con intención de validar si el cuerpo virtual se puede efectivamente reconocer como un sustituto viable del propio cuerpo a nivel del subconsciente. Tras exponer el cuerpo virtual a estímulos nocivos se halla una activación en la corteza motora de los participantes equivalente a la que sería de esperar en un escenario real. Este resultado-como-real hace indicar que los participantes ciertamente aceptan sus cuerpos virtuales dados como su propio cuerpo. En un segundo experimento se estudian las consecuencias de los mecanismos de agencia que nos proporcionan la consciencia de nuestras acciones corporales y motoras, a través de tecnologías de substitución virtual del cuerpo. Los participantes se someten a disrupciones esporádicas de sus acciones mientras realizan movimientos rápidos con su brazo. En algunas ocasiones, la mano virtual del participante se mueve autónomamente y en dirección contraria a la mano real del participante. Los resultados proporcionan evidencias de procesos neuronales específicos responsables de detectar disrupciones de agencia inducidas externamente. Asimismo, estos procesos neuronales se correlacionan con la ilusión de posesión del cuerpo medida a través de cuestionarios. Este estudio profundiza en las perspectivas actuales de los esquemas de agencia, proponiendo y demostrando la teoría existente de mecanismos de errores re-aferentes y de retro-alimentación que funcionan concurrentemente en el cerebro para detectar disrupciones de agencia. Se propone un tercer experimento para explorar las implicaciones de la apariencia externa del cuerpo virtual a la hora de auto-reconocerse. Diseñamos un experimento en el que los participantes se exponen a caras de avatares que se parecen a ellos, a un familiar o a una persona que no conocen. Los resultados muestran mecanismos subyacentes compartidos de auto-identificación de caras reales y virtuales en la corteza visual. En particular, las trazas neurofisiológicas muestran que las caras virtuales se clasifican igual que las reales (en contraste con lo que ocurre durante la clasificación de otros objetos como coches o flores). Además, la corteza visual diferencia niveles de familiaridad entre las caras virtuales. Contribuyendo así de manera novedosa a entender porque avatares con diferente apariencia tienen un impacto en el comportamiento de los participantes, y por ello siendo útil tanto para el campo de la realidad virtual como para el de la auto-identificación. Globalmente, la investigación de esta tesis explora las trazas cerebrales mediante EEG de la experiencia inmediata de poseer y controlar un cuerpo. Se presentan evidencias empíricas para validar el uso de realidad virtual en la investigación de la representación del cuerpo en el cerebro. Asimismo, a través de varios estudios mostramos novedosas trazas neurofisiológicas relacionadas con las manipulaciones corporales y perceptuales. Los resultados y experimentos se contextualizan mediante una revisión en profundidad de la literatura existente en consciencia, percepción corporal y teorías de posesión y agencia del propio cuerpo

    Learning empathy through virtual reality : Multiple strategies for training empathy-related abilities using body ownership Illusions in embodied virtual reality

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    Several disciplines have investigated the interconnected empathic abilities behind the proverb “to walk a mile in someone else’s shoes” to determine how the presence, and absence, of empathy-related phenomena affect prosocial behavior and intergroup relations. Empathy enables us to learn from others’ pain and to know when to offer support. Similarly, virtual reality (VR) appears to allow individuals to step into someone else’s shoes, through a perceptual illusion called embodiment, or the body ownership illusion. Considering these perspectives, we propose a theoretical analysis of different mechanisms of empathic practices in order to define a possible framework for the design of empathic training in VR. This is not intended to be an extensive review of all types of practices, but an exploration of empathy and empathy-related phenomena. Empathy-related training practices are analyzed and categorized. We also identify different variables used by pioneer studies in VR to promote empathy-related responses. Finally, we propose strategies for using embodied VR technology to train specific empathy-related abilities

    Goggles in the lab:Economic experiments in immersive virtual environments

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    This review outlines the potential of virtual reality for creating naturalistic and interactive high-immersive environments in experimental economics. After explanation of essential terminology and technical equipment, the advantages are discussed by describing the available high-immersive VR experiments concerning economic topics to give an idea of the possibilities of VR for economic experiments. Furthermore, possible drawbacks are examined, including simulator sickness, the costs of VR equipment and specialist skills. By carefully controlling a naturalistic experimental context, virtual reality brings some field into the lab. Besides, it allows for testing contexts that would otherwise be unethical or impossible. It is a promising new tool in the experimental economics toolkit

    Agency and responsibility over virtual movements controlled through different paradigms of brain−computer interface

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    Agency is the attribution of an action to the self and is a prerequisite for experiencing responsibility over its consequences. Here we investigated agency and responsibility by studying the control of movements of an embodied avatar, via brain computer interface (BCI) technology, in immersive virtual reality. After induction of virtual body ownership by visuomotor correlations, healthy participants performed a motor task with their virtual body. We compared the passive observation of the subject's ‘own’ virtual arm performing the task with (1) the control of the movement through activation of sensorimotor areas (motor imagery) and (2) the control of the movement through activation of visual areas (steady‐state visually evoked potentials). The latter two conditions were carried out using a brain–computer interface (BCI) and both shared the intention and the resulting action. We found that BCI‐control of movements engenders the sense of agency, which is strongest for sensorimotor areas activation. Furthermore, increased activity of sensorimotor areas, as measured using EEG, correlates with levels of agency and responsibility. We discuss the implications of these results for the neural basis of agency
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