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Majed Samad, Ladan Shams; Visuotactile Synchrony is not a Necessary Condition for the Rubber Hand Illusion. Journal of Vision 2012;12(9):1324. doi: 10.1167/12.9.1324.
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The rubber hand illusion (RHI) (Botvinick & Cohen, 1998) refers to the illusory sense of ownership of a dummy hand that is viewed while being stroked in sync with stroking of one's hidden real hand. The RHI is considered to stem from interactions between vision, touch, and proprioception. We examined the claim that synchronous visuotactile stimulation is necessary for the induction of RHI. Proprioception of the left arm was measured on 40 trials before and after experimental manipulation, which varied across four conditions. In the main condition, a left rubber hand was presented in a position symmetrical to the right arm that was stationed on a table in front of the participant, and tactile stimulation was applied synchronously to the concealed left hand and the visible rubber hand. The second condition was identical except that stroking was asynchronous between the real hand and rubber hand. In the third condition, the rubber hand was present but no tactile stimulation was applied. In the fourth condition, no rubber hand and no tactile stimulation were presented. A significant proprioceptive shift towards the position of the rubber hand was observed in the synchronous stimulation group, whereas the asynchronous group showed no shift. However surprisingly, the majority of participants who were presented with a rubber hand (i.e., first three conditions) experienced a strong illusion of owning the rubber hand even prior to or in the absence of any tactile stimulation. This illusion was not as strong as that following synchronous tactile stimulation, however it was generally rated as vivid. This finding challenges the notion that tactile stimulation is required for the induction of the RHI. These results are discussed in the framework of a Bayesian inference model combining visual and proprioceptive information and involving a prior expectation for hand position consistent with a canonical posture.
Meeting abstract presented at VSS 2012
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