Body-ownership and visual perception

Sammanfattning: The idea that our body plays an important role in visual perception has a long history in storytelling and philosophy. Some ideas are very intuitive. For example, few will disagree with the notion that smaller people perceive the world to be bigger, and vice versa, that larger people perceive the world to be smaller. In contrast, more controversial ideas regarding the role of our body in visual perception have been debated by philosophers. According to these philosophers, the very nature of visual perception lies in the fact that we have a body that moves in space. Since George Berkeley (1685 – 1753) first formalized such a fundamental role for our body in visual perception, different philosophical theories have branched out to account for the latest scientific findings. Although experimental psychologists and neuroscientists have long neglected these intriguing philosophical accounts, the recent development of body-ownership illusions allowed for a more rigorous investigation of the supposed link between our body and visual perception. In body-ownership illusions, research participants experience an artificial body (or body-part) to be their own. These illusions allow for the dissociation between the subjective experience that your body belongs to you (i.e. body-ownership) and the mere visual impression of your body from a first-person perspective. The studies that comprise this thesis use different ownership illusions to investigate the role of body-ownership in visual perception, and the role of visual perception in body-ownership, with visual perception being an umbrella-term for both visuospatial perception and visual awareness. In Study I and Study II we investigated the mechanisms by which body-size influences the perceived size of the world, by having participants experience ownership of different sized (and sometimes invisible) bodies. Our results show that this own-body-size effect does not rely on visual information per se, but instead, on the recalibration between visual and tactile information that updates the representation of external space. In Study III we combine the rubber hand illusion with binocular rivalry to show that body-ownership promotes visual awareness of a fake hand. And in Study IV we combine the rubber hand illusion with continuous flash suppression to show that ownership can be induced in the absence of visual awareness. Such unconscious ownership calls for a reevaluation of the standard definition of body-ownership. Taken together, these studies illuminate the intricate relationship between body-ownership and visual perception. In addition to the scientific research fields of visuospatial perception, visual awareness, and body-ownership, these results are valuable to the philosophical debate on the nature of visual perception and might provide future applications in clinical psychology.