The Impact of Virtual Embodiment on Perception, Attitudes, and Behaviour

[eng] Over the past two decades extensive research in experimental psychology, cognitive neuroscience, and virtual reality has provided evidence for the malleability of our brain's body representation. It has been shown that a person's body can be substituted by a life-sized artificial one, resulting in a perceptual illusion of body ownership over the fake body. Interestingly, several studies have shown that when people are virtually represented with a body different to their own, they exhibit behaviours associated with attributes pertaining to that body. In the research described here we exploited Immersive Virtual Reality to induce body ownership illusions over distinct virtual bodies. We examined how an altered self-representation can influence one's self-perception, perception of the environment, and implicit biases. To this end, we carried out two experimental studies to investigate embodiment of adults in a child virtual body, and a different race virtual body. Moreover, we tested whether it is possible to induce illusory agency over specific actions that are not carried out by the participants themselves. In the Virtual Child Body study, we embodied adults both as a 4-year-old child, and as an adult scaled-down to the same height as the child. The results showed that embodiment in the child body led to a significant overestimation of object sizes, which was approximately double the overestimation of those embodied in the adult body. Moreover, embodiment in the child resulted in changes in implicit attitudes about the self towards being child-like. These findings were diminished under asynchronous visuomotor correlations, providing further proof for the importance of visuomotor contingencies in producing body ownership illusions. Our findings extend and enrich previous research, yielding additional evidence of the malleability of our body representation. In the Racial Bias study, we aimed to explore how the type of body can influence racial discrimination, by embodying white people in a black virtual body. Previous research has shown that this type of embodiment can lead to a reduction of implicit racial bias, but its long-term effects were unknown. Here we tested whether this reduction in implicit bias can (a) be replicated, (b) it can last for at least one week, and (c) it is enhanced by multiple exposures. Participants were immersed in a virtual scenario between one and three times, each separated by two days, and implicit bias was measured one week before their first exposure, and one week after their last. The results showed that implicit bias decreased more for those with the black virtual body than the white, even a week after their virtual exposure, and irrespective of the number of exposures. In the Illusory Speaking study, we explored the possibility of inducing illusory agency over an action that participants did not carry out themselves. We describe a set of experiments, where under appropriate sensorimotor contingencies, we induce a subjective illusion of agency over the participants' speaking virtual body, as if they had been themselves speaking. When participants were asked to speak after this exposure, they shifted the fundamental frequency of their utterances towards that of the stimulus voice of the virtual body. We argue that these findings can be reconciled with current theories of agency, provided that the critical role of both ownership and actual agency over the virtual body are taken into account. Overall, our studies expand previous evidence for the malleability of our body representation, demonstrating how it is possible to induce ownership illusions over a child body, a different race body, or even a speaking body. Notably, we provide evidence of how body ownership and agency over the virtual body result in powerful, lasting changes in perceptual and cognitive processing, having the potential of compelling applications in psychology and neuroscience.[spa] Durante las dos últimas décadas se ha llevado a cabo una amplia investigación que ha permitido descubrir la maleabilidad de la nuestra representación corporal. Se ha demostrado que nuestro cuerpo puede ser sustituido por uno artificial de tamaño real, dando lugar a una ilusión perceptual de posesión de un cuerpo falso (Body Ownership). En la investigación descrita en esta tesis hemos empleado Realidad Virtual Inmersiva con el fin de inducir ilusiones de Body Ownership sobre cuerpos muy diversos. En el estudio del Nino Virtual, ponemos adultos en el cuerpo de un niño, o bien en el de un adulto re-escalado para tener la misma altura que el niño. Los resultados evidencian que la ilusión en el cuerpo del niño conllevó una sobreestimación significativa del tamaño de objetos, la cual era aproximadamente el doble de la estimación dada en el caso del cuerpo del adulto. Además, en el caso del niño virtual la ilusión dio lugar a cambios en la actitud implícita propia hacia un carácter más infantil. En el estudio de la Discriminación Racial, exploramos el modo en que el tipo de cuerpo puede influir en la discriminación racial, poniendo a gente de piel de color blanca en un cuerpo de piel de color negra. En estudios anteriores se ha demostrado que este tipo de ilusión corporal puede conllevar una reducción del sesgo racial implícito. Aquí evaluamos si tal reducción en el sesgo implícito puede a) ser replicada, b) puede durar al menos una semana, y c) se ve incrementada después de múltiples exposiciones. Los resultados muestran que el sesgo implícito disminuyó más en el caso de aquellos participantes que tengan el cuerpo virtual de piel negra incluso una semana después de la exposición virtual. En el estudio de la Ilusión de Hablar exploramos la posibilidad de inducir en los participantes una ilusión de agencia sobre una acción que ellos no llevaron a cabo. Describimos una serie de experimentos donde logramos una ilusión subjetiva de agencia sobre el habla del cuerpo virtual del participante, tal y como si ellos hubieran estado hablando. Cuando pedimos a los participantes que hablaran después de la exposición, modularon la frecuencia fundamental de su tono de voz en la dirección de la voz del cuerpo virtual