Read about all the tactile and body illusions in our special feature
Under normal circumstances, your sense of self is firmly anchored inside your body. Sometimes, though, something goes awry, the connection between body and self breaks down and you have an out-of-body experience.
Such moments occur when brain function is disturbed, such as after a stroke or epileptic seizure, or while on drugs. In 2007, however, two research teams independently reported ways of inducing an out-of-body experience in the lab in normal healthy people.
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The techniques differ slightly, but both involve feeding volunteers video images of themselves from an unusual perspective while applying tactile stimulation, somewhat like the rubber hand illusion.
In the first set-up, a team led by at the Swiss Federal Institute of Technology in Lausanne got volunteers to stand about 2 metres in front of a video camera while wearing goggles, which displayed the video images, converted into a holographic-like 3D projection. This meant that the volunteers could see a version of their own backs. When they stoked the volunteers鈥� backs, many reported a weird feeling that they were somehow inside the virtual body in front of them ().
The volunteers also experienced 鈥減roprioceptive drift鈥� towards the virtual body: they felt as if they were standing in the position of their virtual self. When the researchers turned off the display, moved their volunteers backwards and asked them to return to their original position, many overshot towards where they felt their virtual body had stood.
Last year Blanke鈥檚 team also reported inducing a feeling of out-of-body levitation by repeating the experiment with volunteers who were lying down () Nevertheless, Blanke points out that they have not yet recreated the entire out-of-body experience: 鈥淚t remains an 鈥榓s-if鈥� feeling, but we鈥檙e trying to refine it.鈥�
Ehrsson鈥檚 team have , with seated volunteers filmed from behind while a researcher stands to the side of them stroking the volunteer鈥檚 chest and a space just in front of the camera (see illustration). The volunteers see their own backs, feel the stroking but also see somebody stroking a position just behind them. This strongly creates the illusion that they are outside their own bodies, says Ehrsson (Science, vol 317, p 1048).
What鈥檚 more, when Ehrsson tried swinging a hammer at the previously stroked airspace, it elicited a strong stress response in the volunteer.
Read about all the tactile and body illusions in our special feature
