REVAM: a virtual reality application for inducing body size perception modifications

In this paper, we present a 3D virtual environment for inducing body ownership illusion. The key idea is to take advantage of virtual reality potential regarding body size perception. The application, called REVAM, links two main aspects of body size perception: the first one focuses on its modification and the second one concerns its assessment. Based on some previous evidence that it is possible to modify body-size perception through an illusion of ownership over a virtual body, the application proposes to couple a tactile stimulation when viewing an avatar from a third person perspective (a condition known to produce this kind of illusion). In addition, the application offers the possibility to choose between avatars of different builds, and to perform morphing to reduce the avatars body. Moreover, the application allows to implicitly measure how people perceive their body size from an affordance estimation task in which people have to appreciate if they can pass through doors of different sizes without twisting their shoulders. To test the application we carried out an experiment on 16 female participants who performed the affordance estimation task five times: the first time before being exposed to their chosen avatar to get a baseline measure, and the four other times after being exposed to their avatar in different situations. These different situations are defined by the crossing of two experimental factors: morphing (presence or absence) and simultaneous visuotactile stimulation (presence or absence). A two-way repeated-measures Anova showed a main effect of the morphing: mean door width through which the participants estimate they can fit was significantly reduced (p<.05) when morphing was present. However, this effect did not interact with the presence of a simultaneous tactile stimulation. This indicates that exposing people to a virtual body reduced in size, as proposed in the present application, could be an effective way to modify body size perception, at least temporarily. The final goal would be to help patients with body image disorders, such as anorexia nervosa.