Body ownership affects visual perception of object size by rescaling the visual representation of external space

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.     

How does evidence-based practice in psychology work? – As an ethical demarcation

Evidence-based practice in psychology (EBPP) is ordinarily understood to demarcate between legitimate and illegitimate psychotherapy practice, based upon the epistemic demarcation distinguishing scientific from non-scientific knowledge. EBPP emphasizes the value of effective and efficient interventions identified through randomized controlled trials and cost-benefit analyses. Basing the template for choice of action or strategy on randomized controlled trials and cost-benefit analyses create a deceptive appearance of ethical neutrality. However, there is an implicit ethical demarcation at work in EBPP, which favors a non-articulated specific position in normative ethics. More particularly, evidence-based practice in psychology is structured according to a utilitarian framework, severely limiting the kinds of ethical perspectives available to assess psychotherapy practice. The latter point is illustrated through a new mode of delivering psychotherapy services called “Internet-based guided self-help” (IBGSH). In EBPP the only relevant ethical question is to what extent any intervention, such as IBGSH, is effective and efficient. Some of the limiting effects of the ethical, utilitarian, demarcation are showcased by presenting three alternative ethical perspectives by which psychotherapy practice in general and IBGSH in particular can be analyzed. The analysis concludes that EBPP is not suited to ethically regulate the practice of psychotherapy.