Abstract
BackgroundAltering the normal association between touch and its visual correlate can result in the illusory perception of a fake limb as part of our own body. Thus, when touch is seen to be applied to a rubber hand while felt synchronously on the corresponding hidden real hand, an illusion of ownership of the rubber hand usually occurs. The illusion has also been demonstrated using visuomotor correlation between the movements of the hidden real hand and the seen fake hand. This type of paradigm has been used with respect to the whole body generating out-of-the-body and body substitution illusions. However, such studies have only ever manipulated a single factor and although they used a form of virtual reality have not exploited the power of immersive virtual reality (IVR) to produce radical transformations in body ownership.Principal FindingsHere we show that a first person perspective of a life-sized virtual human female body that appears to substitute the male subjects' own bodies was sufficient to generate a body transfer illusion. This was demonstrated subjectively by questionnaire and physiologically through heart-rate deceleration in response to a threat to the virtual body. This finding is in contrast to earlier experimental studies that assume visuotactile synchrony to be the critical contributory factor in ownership illusions. Our finding was possible because IVR allowed us to use a novel experimental design for this type of problem with three independent binary factors: (i) perspective position (first or third), (ii) synchronous or asynchronous mirror reflections and (iii) synchrony or asynchrony between felt and seen touch.ConclusionsThe results support the notion that bottom-up perceptual mechanisms can temporarily override top down knowledge resulting in a radical illusion of transfer of body ownership. The research also illustrates immersive virtual reality as a powerful tool in the study of body representation and experience, since it supports experimental manipulations that would otherwise be infeasible, with the technology being mature enough to represent human bodies and their motion.
Highlights
When something strikes our body we feel it at the same place that we see it
When normal correlation between two sensory streams is changed, for example, by seeing a plausibly located rubber hand touched while simultaneously feeling the touch on our out-ofsight real hand, the brain apparently engages in a re-evaluation of probabilities and assigns ownership to the visible rubber limb [1,2]
Touch refers to whether the subject felt synchronously (TS) or asynchronously (TS9) touched on his shoulder when the standing woman stroked the shoulder of the seated girl (Figure 2C, 2D, 2F)
Summary
When something strikes our body we feel it at the same place that we see it. When normal correlation between two sensory streams is changed, for example, by seeing a plausibly located rubber hand touched while simultaneously feeling the touch on our out-ofsight real hand, the brain apparently engages in a re-evaluation of probabilities and assigns ownership to the visible rubber limb [1,2]. These methods have been used to produce illusions of body morphing, adding supernumery limbs to the body [3,4,5,6], and outof-the-body experiences [7,8,9]. Such studies have only ever manipulated a single factor and they used a form of virtual reality have not exploited the power of immersive virtual reality (IVR) to produce radical transformations in body ownership
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