Embodiment and the Self: using Virtual Reality and Full Body Illusion to change bodily self-representation, perception and behaviour

Virtual Reality (VR) is an important tool for researchers of many different fields, from cognitive neuroscience to social psychology. The present work will explore the use of VR, and in particular of immersive virtual reality (IVR), in the study of some key aspects of our bodily self and bodily related behaviour and perception. In the first part of the present work we will discuss the combined used of IVR and full body illusion (FBI) in the study of body image distortion (BID) in anorexia nervosa (AN). The first chapter will serve as a general introduction to AN and its most prominent clinical characteristics, as well as introducing some key concepts like the malleability of the bodily-self through multisensory bodily illusions and a brief overview of a series of studies that applied both IVR and embodiment illusions to manipulate participants’ body representation. The second chapter will present a study in which we used the embodiment illusion of different sized avatars to characterize and reduce both the perceptual (body overestimation) and cognitive-emotional (body dissatisfaction) components of BID in AN. For this study we built personalized avatars for each participants (healthy controls (HC) and AN patients) and applied synchronous and asynchronous interpersonal multisensory stimulation (IMS) to three different virtual bodies (the perceived one, a +15% fatter one and a -15% thinner one). The different components of BID were measured by asking participants to choose the body that best resembled their real and ideal body before and after the embodiment illusion was induced. The results of this study showed a higher body dissatisfaction in AN patients, who also reported stronger negative emotions after being exposed to the largest avatar. However, the embodiment procedure did not affect BID in AN patients. Based on the results of the previous study, in the study presented in the third chapter we decided to shift our focus from somatorepresentation, i.e. the explicit representation of the body which comprise both cognitive and emotional components of body image, to somatoperception, i.e. the implicit representation of the body which comprise both body perception and body schema. In this study we applied a FBI over an underweight (BMI = 15) and normal weight (BMI = 19) avatar and measured the effect of the embodiment illusion on participants’ (AN and HC) body perception and body schema estimations. To measure body perception, we asked participants to estimate the width of their hips while their vision was blocked, whereas for the body schema estimation participants had to estimate the minimum door’s aperture width in order to pass through it inside an IVR scenario. The results showed that AN patients reported an overestimation in both body perception and body schema estimations. Furthermore, in AN patients we saw a change in the body schema estimation accordingly to the size of the embodied avatar, thus showing a higher bodily self-plasticity compared to HC. In the fourth chapter of the present work we will go over the results of the two aforementioned studies and will briefly discuss some possible future directions. Finally, the last two chapters of the thesis will present two research projects that will respectively utilize IVR and the embodiment illusion for the study of individual dishonest behaviour in digital interactions (chapter 5) and for the modulation of acute and chronic pain (chapter 6). As the COVID-19 pandemic deeply affected the work on both these studies, these two final chapters will only present a general introduction and the methods/technical implementation for both research projects.