The fascinating new study “If I Were You: Perceptual Illusion of Body Swapping” published this week by the Swedish researchers Henrik Ehrsson and Valeria Petkova has been making the rounds and drawing some press – see Neurophilosophy and Neuroanthropology for background and explanation - but what seems to have been lost in all the excitement over the body’s proven ability to perceive another body as its own are the largely unexplored limitations to that illusion.
After having elicited a body-swap illusion in the test subjects, Ehrsson and Petrova conducted a variation thereof using a “dark green rectangular box of the same height and width” as a human body, to show that the subject can’t simply swap bodies with anything.
“We also conducted an experiment to examine our prediction that the body would need to look like a human to be experienced as one’s own. Pilot experiments suggested that the illusion did not work with objects that do not resemble a human body, such as boxes, chairs and tables. Thus we conducted an experiment where we applied threats to the mannequin or to a rectangular object of the same size, after a period of synchronous or asynchronous visuo-tactile stimulation to the respondent and the object.”
While these results suggest that a nearly exact correlation between forms is necessary for a truly immersive illusion to follow, the choice of a box, as counter-model, passes over a vast terrain of possible human-like, if still non-human, surrogate forms. Elicited out-of-body experiences like Jaron Lanier’s VR jaunt as a lobster, which I briefly went over here, is one example of the many extra-human immersive possibilities obscured by the box counter-example.
The study concludes however with a ‘common sense’ remark that the body-swap illusion is only possible with bodies that “resemble” one’s own, but, again, it is simply not clear what constitutes resemblance. We already know from experiments with immersion that non-human appendages can localize sensory experiences and that sensory-motor adaptation can radically exceed its original configuration. To what extent, then, can these kinds of limits be pushed or rearranged? Is it possible, for instance, to design a sophisticated training regimen that could progressively coach adaptation to surrogate forms that would otherwise not be immediately psychically acceptable? Perhaps in the coming years experiments will take a greater interest in manipulating the seemingly permanent forms of body identification.
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