Study using hands made of rubber shows skin color is not important in sensations

Taking pointers from rubber hands, psychologists have shown that racial differences really are only skin deep.

It was already known that when a person sees a rubber hand being stroked while his own hand is hidden from view and stroked simultaneously, he can begin to “embody” the rubber hand, feeling it as his own and losing feeling in his own hand.

But can you embody a rubber hand whose color is different from your own? Manos Tsakiris and colleagues at Royal Holloway, a college that is part of the University of London, induced the illusion in 22 white participants, using both white and black rubber hands. Later, the subjects claimed, on average, to have identified more strongly with the white hand.

Objective measures suggested otherwise, though. For instance, researchers tested changes in skin conductance — a measure of stress — when the subjects saw a needle being stuck into the embodied rubber hand. In theory, the more the subject identifies with the rubber hand, the greater this stress response.

Yet subjects were just as stressed watching the needle puncture the black hand as the white one.

Another measure of the strength of the illusion is proprioceptive drift, a shift in the perceived location of the real hand. The volunteers showed the same amount of drift regardless of the color of the rubber hand.

“The processes that are involved in the illusion aren’t particularly sensitive to the skin color of the hand,” said Harry Farmer, member of the research team.

“The way that the brain defines who we are doesn’t care that much about the surface features; it cares about actual sensory experiences,” added Patrick Haggard of University College London, who was not involved in the work.

— This article was produced by New Scientist magazine, which can be read online at www.newscientist.com

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