51动漫

By deliberately scrambling a person鈥檚 visual and tactile senses, it is now possible to give them an 鈥渙ut-of-body鈥� experience.

Two procedures 鈥� which are the first to imitate an out-of-body experience artificially 鈥� use cameras to fool people into thinking they are standing or sitting somewhere else in a room. They provide the strongest proof yet that people only imagine floating out of their bodies during surgery or near-death experiences.

鈥淭he brain can trick itself, and when it is trying to interpret sensory information, the image it produces doesn鈥檛 have to be a real representation,鈥� says Henrik Ehrsson, of the Institute of Neurology, University College London, UK, who designed the first experiment.

To trick his subjects, Ehrsson had them wear a head-mounted display that showed them footage of themselves filmed from behind, while preventing them from seeing anything else. He then used a plastic rod to prod the subject in the chest and simultaneously held a second rod in front of the camera behind them, to make it seem that the illusory 鈥減erson鈥� viewed from behind was being prodded in the chest too.

Subjects physically felt themselves being prodded, but also had the weird sensation that it was their alter ego in the film footage being prodded. 鈥淚t gives you a very strong sensation you鈥檙e sitting somewhere else,鈥� Ehrsson said at a press conference held in London.

Not madness

His conclusion is that our perception of self within the body is tightly bound to how our brains process information from our senses. 鈥淚鈥檓 not interested in out-of-body experiences,鈥� says Ehrrson. 鈥淚鈥檓 interested in why I, as myself, am located in my body 鈥� why we have 鈥榠n-body鈥� experiences, if you like.鈥�

He says the work is important because it de-stigmatises reports of out-of-body experiences by people who are on drugs, or ill with conditions such as migraine or epilepsy. 鈥淭hey don鈥檛 have to be mad to experience these things,鈥� he says.

Ehrrson鈥檚 results are echoed by a second out-of-body experiment, conducted by Olaf Blanke and colleagues at the Federal Polytechnic of Lausanne (EPFL) in Switzerland. This group also deliberately scrambled the visual and tactile experiences of subjects to create a sense of disembodiment.

In Blanke鈥檚 set-up, people were fitted with 3D headsets and forced to watch virtual 鈥渇igures鈥� standing two metres ahead being stroked on the back.

They either saw live footage of themselves, of a dummy, or of an inanimate black board being stroked. Sometimes the subjects themselves were stroked at the same time, and sometimes not.

After watching the images for a minute, the subjects were blindfolded, move directly backwards and asked to walk forward to where they had been originally standing.

Relocated self

Blanke found that those who had seen either themselves or the dummy being stroked while also being stroked, overshot their original position by 25 centimetres on average, suggesting they were drawn towards the 鈥減erson鈥� they had watched, thinking it was actually them. But the trick did not work if they watched the blackboard being stroked, or if they had not simultaneously been stroked.

Blanke says the experiment demonstrates that the sight of a human-like figure combined with stroking can trick a person into subconsciously relocating their sense of self away from where it should have been. 鈥淭he self was no longer within the body borders,鈥� he said at the same press conference. But he admits that the illusion did not create a full 鈥渙ut-of-body鈥� experience like Ehrsson鈥檚.

Both researchers say their experiments reinforce the idea that the 鈥渟elf鈥� is closely tied to a 鈥渨ithin-body鈥� position, which is dependent on information from the senses. 鈥淲e look at 鈥榮elf鈥� with regard to spatial characteristics, and maybe they form the basis upon which self-consciousness has evolved,鈥� says Blanke.

The researchers add that the procedures could perhaps be used to create more realistic avatars in virtual reality computer games. The same technology might also be used to enable tasks such as surgery to be carried out remotely, linking distant surgeons more realistically to remotely-operated surgical tools.

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