The Magnetic Touch Illusion: Perceiving a “Force field” in an Alien Limb

fake-rubber-hand


A new study demonstrates an illusion where participants experience a strange sensation of illusory ‘magnetic’ interaction between a tool and their hand. However it’s not actually their hand.

Ownership of your limbs is something generally not questioned. If our time were consumed by uncertainty of our limbs, it would be highly debilitating. However, one can be ‘tricked’ into adopting a rubber hand for their own – a feat that multisensory researchers have been investigating since the dawn of the ‘rubber hand illusion.’ For those not familiar, this illusion can occur when one views a rubber hand while their actual hand is placed out of view. When an experimenter brushes both the rubber hand and the participant’s hand simultaneously with a paintbrush, the participant ‘feels’ the tactile sensation as though it’s coming from the rubber hand and not their own hand. The participant ‘feels’ ownership of the rubber hand in the very same way as their own hand. The illusion has been studied extensively, revealing insight primarily regarding multisensory integration and embodiment.

In the October issue of Cognition, Arvid Guterstam (Erhsson Lab) and colleagues have published an intriguing examination of an extension of the rubber hand illusion; The Magnetic Touch Illusion. This arrangement, originally conceived of by Jakob Hohwy and Brian Paton, procures a qualitatively different sensation involving the feeling of a “force field” around an alien limb, for which ownership is similarly claimed.

Although the study involves eight experiments, the illusion results from a simple manipulation of the basic rubber hand illusion setup. While the experimenter brushes the participant’s hidden fingers, s/he brushes the space around the rubber hand (instead of brushing the rubber hand itself), clearly making it visible that s/he is not actually making contact with the rubber hand. According to the study, this variation is unique because it produces a sensation of multisensory visual-tactile integration within peripersonal space. Participants described this feeling as a ‘‘repelling magnetic force”, a ‘‘force field”, or ‘‘invisible rays of touch.”

From the series of experiments the authors were able to demonstrate that the illusion persisted with brush strokes around the rubber hand up to a distance of about 40 cm and that the illusion was spatially anchored to the rubber hand – it followed the rubber hand when the hand was moved. It was also concluded that the integration of visual and tactile information was crucial – simply moving the brush closer to the rubber hand in a manner that implies an expected contact did not elicit the effect. In addition, they showed visible solid barrier around the rubber hand similarly prevents the illusion from occurring.

From an experiential perspective, one can imagine the magnetic touch illusion severely blurs the boundary between self and other that’s normally perceived very clearly and effortlessly. However, from a knowledge-based perspective, the authors state “The present findings offer an important advancement in understanding of the relationship between the representation of peripersonal space and the sense of body ownership—two processes related to the construction of a multisensory boundary separating the body from the external environment.”

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