Explaining Away the Body: Experiences of Supernaturally Caused Touch and Touch on Non-Hand Objects within the Rubber Hand Illusion

Jakob Hohwy,Bryan Paton,Antoni Rodriguez-Fornells

doi:10.1371/journal.pone.0009416

Abstract

BackgroundIn rubber hand illusions and full body illusions, touch sensations are projected to non-body objects such as rubber hands, dolls or virtual bodies. The robustness, limits and further perceptual consequences of such illusions are not yet fully explored or understood. A number of experiments are reported that test the limits of a variant of the rubber hand illusion.Methodology/Principal FindingsA variant of the rubber hand illusion is explored, in which the real and foreign hands are aligned in personal space. The presence of the illusion is ascertained with participants' scores and temperature changes of the real arm. This generates a basic illusion of touch projected to a foreign arm. Participants are presented with further, unusual visuotactile stimuli subsequent to onset of the basic illusion. Such further visuotactile stimulation is found to generate very unusual experiences of supernatural touch and touch on a non-hand object. The finding of touch on a non-hand object conflicts with prior findings, and to resolve this conflict a further hypothesis is successfully tested: that without prior onset of the basic illusion this unusual experience does not occur.Conclusions/SignificanceA rubber hand illusion is found that can arise when the real and the foreign arm are aligned in personal space. This illusion persists through periods of no tactile stimulation and is strong enough to allow very unusual experiences of touch felt on a cardboard box and experiences of touch produced at a distance, as if by supernatural causation. These findings suggest that one's visual body image is explained away during experience of the illusion and they may be of further importance to understanding the role of experience in delusion formation. The findings of touch on non-hand objects may help reconcile conflicting results in this area of research. In addition, new evidence is provided that relates to the recently discovered psychologically induced temperature changes that occur during the illusion.

Highlights

In an intriguing type of illusion, touch sensations can be felt as produced on objects, such as rubber hands, mannequins or virtual bodies, located away from participants’ real limbs or bodies [1,2,3,4,5,6]
We find that without prior onset of the basic illusion there is no significant difference between reports of a rubber hand illusion (RHI)-like illusion for the non-hand object during synchronous touch vs. asynchronous touch
There was support for the secondary hypothesis that the odd experience of feeling a touch as if on a cardboard box would not arise without prior onset of the basic illusion

Summary

Introduction

In an intriguing type of illusion, touch sensations can be felt as produced on objects, such as rubber hands, mannequins or virtual bodies, located away from participants’ real limbs or bodies [1,2,3,4,5,6] These illusions arise in an effort to integrate conflicting visuotactile stimuli, and this process can override prior knowledge of the visual body-image, proprioception or selflocation, as well as general background knowledge. To gain a better understanding of such phenomena is it desirable to investigate their robustness, limits and their consequences for further sensory processing It is investigated whether, subsequent to the onset of such an illusion, unusual visuotactile stimuli are incorporated into them, that is, whether there can be further visuotactile illusions within a version of the rubber hand illusion. A number of experiments are reported that test the limits of a variant of the rubber hand illusion

Methods

Results

Conclusion