To do voodoo or not to do

Voodoo dolls are a form of sympathetic magic used to cast spells on certain people – supposedly, they’re usually for good luck rather than to hurt the person involved.

But this is “Lost in Science”, not “Lost in Magic”, so instead we’re going to look at the scientific equivalent, where Swedish researchers were able to get people to identify with doll-sized, or even giant-sized, artificial bodies.

Experimental set-up showing the artificial bodies and how experimental subjects were first made to identify with them and then to gain distorted perception of object sizes and distance
(A) The main experimental set-up for the body-swap test, (B) the four artificial bodies, (C) the image seen by participants during visuo-tactile stimulation, (D) the Barbie doll experiment, (E) object size estimation and (F) distance estimation.

In this experiment, participants lying on a bed wore head-mounted displays through which they saw an artificial body instead of their own. By touching both the doll’s and the human’s legs at the same time, after 4 minutes they’d gotten the person to identify with the doll body as their own (this was confirmed by cutting the doll with a knife and measuring signs of anxiety in the subject’s skin conductance).

The result was that, when the person thought they had a doll-sized body, they saw objects and distances as being much bigger than they really are; and of course they experienced the opposite with the giant body. These effects even continued after the people were “disconnected” from the doll, and asked to walk a given distance blindfolded.

This experiment not only demonstrates how easy it is to swap identity with an artificial body, but also how much our perceptions of size depend on what we’re comparing it to.

van der Hoort B, Guterstam A & Ehrsson HH 2011, “Being Barbie: the size of one’s own body determines the perceived size of the world”, PLoS ONE 6(5): e20195, doi:10.1371/journal.pone.0020195

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