Most of us take for granted that our body is our body. One typically experiences one’sbody as something belonging just to oneself, as something that can only be “me”.However, this poses a fundamental problem in philosophy and psychology: how dowe know that the body is our own? It has been suggested that two distinct experiencesof our own body help us recognize it as such: the sense of ownership, that is theexperience that a limb is part of one’s body, and the sense of agency, that is theexperience of being able to voluntarily control limb movement. In the present thesis weintroduce a new version of the classical rubber hand illusion that is based on fingermovements instead of stroking and systematically investigate how ownership andagency contributes to bodily self-recognition. To induce “the moving rubber hand illusion” participants control the movements ofthe index finger of a right wooden model hand in full view by moving their own rightindex finger, which is hidden from view. The illusion is quantified subjectively withvisual analogue rating scales and behaviourally as changes in manually indicatedsensed hand position (“proprioceptive drift”). In 9 separate experiments involving atotal of 352 healthy volunteers we first characterized the basic constrains of the illusion.Secondly, we examined the relationship of ownership and agency. And finally,investigate a possible relationship between the illusion and individual differences indelusion proneness (using Peter’s Delusion Inventory). Our results show that synchronized movements of the model’s index finger and theparticipant’s index can trigger a strong illusory feeling of ownership of the model handand robust experience of agency. The moving rubber hand illusion is similarly strong asthe classical version, and follows similar temporal, spatial and anatomical rules.Asynchronous seen and felt finger movements, a too great distance between the realand model hands (≥27 cm), or the model placed in an anatomically implausible positionabolishes the ownership-illusion. We also found that ownership and agency can be dissociated. Unlike ownership,agency can be experienced for the model hand when it is when placed in ananatomically implausible position. And ownership can be experienced irrespective ofthe hand moving actively or passively, so with or without agency. Furthermore onlyownership, but not agency ratings correlate with the proprioceptive drift. Finally, weobserved that delusion prone-individuals tend to give generally higher overall ratingson agency, when they experience the hand moved passively. Collectively, these observations advance our understanding of how ownership andagency contribute to bodily self-recognition. Ownership and agency constitute differentprocesses: Integration of spatio-temporally congruent signals from moving limbsdetermine the sense of ownership and a match of movement intentions and feedbackdetermines the sense of agency. These results offer new ways to study bodily selfrecognitionboth at the behavioural and neural level.
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