The classic ‘rubber hand illusion’ gives profound insight to our brain’s ability to confuse the real and living with the inanimate. Originally reported by Matthew Botvinick and Jonathan Cohen in 1998, when people have their hand hidden from view and watch a dummy hand being stroked with a paintbrush while their hidden hand is also stroked, they feel the stroke to be coming from the dummy hand rather than their real hand.
This illusion demonstrates that our perception of body-part ownership is malleable, complementing evidence I mentioned in a previous post suggesting that patients with amputated limbs can still feel pain in their missing limbs. Studies of the rubber-hand illusion have helped us understand how we recognize our body parts and how that might change if we were to lose or replace a body part. Moreover, they have helped us understand the relationships among vision, somatosensation (the sense of touch) and proprioception (the sense of body-part location).
However, it turns out that the illusion doesn’t only need to be studied with rubber hands – it can also be induced with a virtual representation of hands. In this ‘virtual arm illusion,’ people who view a 3D virtual arm instead of a rubber arm, under the same conditions as Botvinick and Cohen’s illusion, confuse their real arm with the arm displayed in virtual reality. Since it easier to experimentally manipulate virtual images and scenes than a rubber object, the virtual arm illusion could be used as an important tool to build on findings from rubber hand studies.
Indeed, in a new study by the researchers who originally reported the virtual arm illusion, they demonstrate that the illusion extends beyond the sense of touch. Subjects who had their hand blinded from view wore 3D goggles and watched a virtual hand move either in synchrony or asynchrony with their actual hand movement. The subjects felt a sense of ownership over the virtual hand when it was moving in synchrony with real hand movement, but they felt that they had significantly less control over the virtual hand with their real hand was moving differently.
The authors suggest that their findings could provide insight to the use of virtual bodies in therapies and rehabilitation. But what about this (slightly more commercially-driven) application: 3D movies where you feel like you are literally part of the film, moving around a scene, feeling yourself touching supposedly virtual objects, supposedly virtual people??
Toying with our sense of body ownership using virtual manipulations could further bridge the fading gap between science-fiction and reality. And help us understand the living electricity encased in our skulls along the way.
Sanchez-Vives MV, Spanlang B, Frisoli A, Bergamasco M, & Slater M (2010). Virtual hand illusion induced by visuomotor correlations. PloS one, 5 (4) PMID: 20454463