When right feels left: referral of touch and ownership between the hands

Valeria Ivanova Petkova, Henrik Ehrsson
Poster
Time: 2009-07-02  09:00 AM – 10:30 AM
Last modified: 2009-06-04

Abstract


Feeling touch on a body part is paradigmatically considered to require stimulation of tactile afferents from the body part in question, at least in healthy non-synaesthetic individuals. In contrast to this view, we report a perceptual illusion where people experience “phantom touches� on a right rubber hand when they see it brushed simultaneously with their left hand. Such illusory duplication and transfer of touch from the left to the right hand was only elicited when a homologous pair of hands was brushed in synchrony for an extended period of time. This stimulation caused 16 out of 30 participants to perceive the right rubber hand as their own and to sense two distinct touches – one located on the right rubber hand and the other on their left (stimulated) hand. We found a significant correlation between experiencing the duplication of touch and the feeling ownership of the rubber hand (N = 30, p = 0.021, two-tailed Pearson correlation; r = .418). This effect was supported by behavioral data associated with misreaching in a pointing task when asked to localize the position of the participant’s own right hand. There was a significant reaching error towards the right rubber hand when it was brushed in synchrony with the left real hand as compared to the asynchronous mode of brushing which was the control condition (N = 14, p = .012, two-tailed t-test). Physiological evidence obtained by skin conductance responses when threatening the model hand revealed that people displayed greater emotional responses when we stabbed the rubber hand with the needle after the illusion condition than they did under two appropriate control conditions (N = 14, p = 0.028, F = 4.138, df = 2, one-way repeated measures ANOVA). Our findings suggest that visual information augments subthreshold somatosensory responses in the ipsilateral hemisphere, thus producing a tactile experience from the non-stimulated body part. These findings are of fundamental importance because they reveal how multisensory interactions between the hands cause qualitative changes in unimodal tactile perception, and that this has a direct consequence for how we come to experience limbs as part of our own body. Our finding could have a bearing on applied neuroscience, as tactile stimulation to an intact hand in amputees might support the ownership and usage of prosthetic limbs. Similarly, research on stroke rehabilitation should examine the possibility that physiotherapy of a hemiplegic limb might be facilitated by concurrent tactile stimulation of the contralateral limb.

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