Body representation and pain relay on complex, multisensory factors. Looking at one's own body induces analgesia, we hypothesize that this effect is due to an interaction between ongoing information from body representation and pain experience, thus manipulations of the former, should affect the latter.
We measured either physiological responses to pain (SCR) and subjective experience (pain ratings) in three studies.
In the first study we investigated whether changes in illusory self-identification with an avatar, induced during the Full Body Illusion by congruent visuo-tactile stroking of the participant and an avatar, reduces the response to pain compatibly with the feeling of the participants to be looking to their own biological bodies.
In the second study we introduced visual manipulations of body representation, namely the magnification or the shrinking of the participant's hand, while this was targeted by noxious stimuli.
In the third study we combined the first two experiments, testing whether the size manipulation applied to an embodied avatar, induces similar effects to those induced by the visual manipulation of the real hand.
We found a reduction of SCR to painful stimuli which was related to the level of avatar embodiment. Moreover, the visual size manipulation showed congruent results when applied either to the biological and the embodied virtual body: decreased SCR was found for body visual magnification , while no effect followed body shrinking. Interestingly pain ratings showed a significant reduction only for the manipulation of the real body.
The present results witness for the idea that body representation and pain experience are strictly related, so that manipulations of body representation can affect the physiological processing of painful stimuli. On the other hand, the subjective pain rating was modulated only by the visual manipulation of a real body, suggesting that the modulation of explicit painful experience is harder to achieve by means of bodily illusions. This might be truth considering that the ownership felt under illusory conditions is heterogeneous and less strong than those felt towards one's own biological body.