title: Body ownership affects visual perception of object size by rescaling the visual representation of external space.
abstract: Size perception is most often explained by a combination of cues derived from the visual system. However, this traditional cue approach neglects the role of the observer's body beyond mere visual comparison. In a previous study, we used a full-body illusion to show that objects appear larger and farther away when participants experience a small artificial body as their own and that objects appear smaller and closer when they assume ownership of a large artificial body ("Barbie-doll illusion"; van der Hoort, Guterstam, & Ehrsson, PLoS ONE, 6(5), e20195, 2011). The first aim of the present study was to test the hypothesis that this own-body-size effect is distinct from the role of the seen body as a direct familiar-size cue. To this end, we developed a novel setup that allowed for occlusion of the artificial body during the presentation of test objects. Our results demonstrate that the feeling of ownership of an artificial body can alter the perceived sizes of objects without the need for a visible body. Second, we demonstrate that fixation shifts do not contribute to the own-body-size effect. Third, we show that the effect exists in both peri-personal space and distant extra-personal space. Finally, through a meta-analysis, we demonstrate that the own-body-size effect is independent of and adds to the classical visual familiar-size cue effect. Our results suggest that, by changing body size, the entire spatial layout rescales and new objects are now perceived according to this rescaling, without the need to see the body.
authors.affiliation: Department of Neuroscience, Karolinska Institutet, Retziusväg 8, 17177, Stockholm, Sweden, bjorn.van.der.hoort@ki.se.
authors.forename: Björn
authors.initials: B
authors.lastname: van der Hoort
authors.forename: H Henrik
authors.initials: HH
authors.lastname: Ehrsson
mesh_terms: D000328:Adult; D003463:Cues; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D008297:Male; D009903:Optical Illusions / Q000502:physiology*; D010067:Ownership; D010550:Personal Space; D012858:Size Perception / Q000502:physiology*