Moving a rubber hand : the sense of ownership and agency in bodily self-recognition

Most of us take for granted that our body is our body. One typically experiences one’s
body as something belonging just to oneself, as something that can only be “me”.
However, this poses a fundamental problem in philosophy and psychology: how do
we know that the body is our own? It has been suggested that two distinct experiences
of our own body help us recognize it as such: the sense of ownership, that is the
experience that a limb is part of one’s body, and the sense of agency, that is the
experience of being able to voluntarily control limb movement. In the present thesis we
introduce a new version of the classical rubber hand illusion that is based on finger
movements instead of stroking and systematically investigate how ownership and
agency contributes to bodily self-recognition. 



To induce “the moving rubber hand illusion” participants control the movements of
the index finger of a right wooden model hand in full view by moving their own right
index finger, which is hidden from view. The illusion is quantified subjectively with
visual analogue rating scales and behaviourally as changes in manually indicated
sensed hand position (“proprioceptive drift”). In 9 separate experiments involving a
total 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 in
delusion proneness (using Peter’s Delusion Inventory). 



Our results show that synchronized movements of the model’s index finger and the
participant’s index can trigger a strong illusory feeling of ownership of the model hand
and robust experience of agency. The moving rubber hand illusion is similarly strong as
the classical version, and follows similar temporal, spatial and anatomical rules.
Asynchronous seen and felt finger movements, a too great distance between the real
and model hands (≥27 cm), or the model placed in an anatomically implausible position
abolishes 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 an
anatomically implausible position. And ownership can be experienced irrespective of
the hand moving actively or passively, so with or without agency. Furthermore only
ownership, but not agency ratings correlate with the proprioceptive drift. Finally, we
observed that delusion prone-individuals tend to give generally higher overall ratings
on agency, when they experience the hand moved passively. 



Collectively, these observations advance our understanding of how ownership and
agency contribute to bodily self-recognition. Ownership and agency constitute different
processes: Integration of spatio-temporally congruent signals from moving limbs
determine the sense of ownership and a match of movement intentions and feedback
determines the sense of agency. These results offer new ways to study bodily selfrecognition
both at the behavioural and neural level