Abstract
Body ownership can be experimentally investigated with the rubber hand illusion (RHI), in which watching a rubber hand stroked synchronously with one’s own hidden hand induces a feeling of ownership over the rubber hand. The aim of this study was to investigate response to the RHI in high (N = 21) and low (N = 19) hypnotizable individuals in normal waking state and in hypnosis. Response to the RHI was measured via a question on the illusory feeling of ownership and with proprioceptive drift. The Highs expressed an overall feeling of more ownership over the rubber hand in both the normal waking state and hypnosis, although both groups gave higher ownership scores after synchronous than after asynchronous stroking and the difference between conditions was similar across groups. Conversely, the proprioceptive drift appeared to be differentially modulated by hypnosis and hypnotic suggestibility: it was increased in the Highs and decreased in the Lows after hypnosis induction. These findings hint at an interplay between hypnotic suggestibility and hypnosis in modulating response to the RHI. The selective breakdown of proprioceptive drift among the Lows suggests resistance to recalibrate one’s own limb in hypnosis.
Highlights
Body ownership can be experimentally investigated with the rubber hand illusion (RHI), in which watching a rubber hand stroked synchronously with one’s own hidden hand induces a feeling of ownership over the rubber hand
After comparing the two mental states within each group, we found a difference between hypnosis and normal waking state with regards to the asynchronous condition, selectively for the Lows (Z = −2.55, p = 0.011, r = −0.414), whereas no statistically significant difference between normal waking and hypnosis was found for the Highs (Fig. 3A)
We found a dissociated pattern between the two components of the illusion: for the illusory feeling of ownership the very same pattern could be observed for the two groups, with higher scores recorded after synchronous than after asynchronous stroking in normal waking state and in hypnosis, whereas the proprioceptive drift appeared to be differentially modulated by hypnosis and hypnotic suggestibility and was increased in the Highs and decreased in the Lows after hypnosis induction
Summary
Body ownership can be experimentally investigated with the rubber hand illusion (RHI), in which watching a rubber hand stroked synchronously with one’s own hidden hand induces a feeling of ownership over the rubber hand. Hypnosis offers a good opportunity to experimentally investigate alterations of bodily self-consciousness in healthy participants safely With this explorative study we wanted to investigate whether the sense of body ownership is influenced by hypnotic induction and suggestibility. While Highs present deactivation of the anterior default mode network during hypnosis[18] and increased activity with increasing depth of hypnosis in some prefrontal regions[20], Lows present decreased activity in the insula[18], which is involved in the RHI, and especially in proprioceptive drift[22] Based on this evidence we hypothesized that response to the RHI may vary according to an individual’s level of hypnotic suggestibility and to the actual mental state. The current study is an explorative investigation into the role of normal waking state and hypnosis in influencing susceptibility to the two components of the RHI (illusory feeling and proprioceptive drift) in Highs and Lows. Our prediction is that higher sensory suggestibility scores will be associated with stronger illusory feeling of ownership, as found in our previous study[12]
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