That arm is mine...
As well as creating a sensation that a missing limb is present, the human brain can be fooled into thinking that an inanimate object is part of the body.
If a subject’s hand is hidden and a rubber hand placed in view, simultaneously stroking the hidden hand and the rubber hand conjures up a sense that the rubber hand is part of the body. What’s more, threatening the rubber hand – with a sharp implement – elicits a feeling of anxiety and a desire to move the hand away from the threat.
These results suggest that artificial limbs could be made to feel as if they are a genuine part of the body, providing input beyond simple proprioceptor-like positional information or a sense of touch. This feeling of ownership is also linked to activity in the interoceptive areas of the brain, which focus on the detection of internal states. (For more on interoception, see our Inside story article.)
Researchers have also managed to take this a step further and create an illusion that a subject’s entire body is located elsewhere – a true ‘out of body’ experience.
In one experiment subjects were given a video headset so that they could see a view of themselves from behind. An experimenter rubbed their chests with a rod, but subjects could only see a rod situated behind them, ‘rubbing’ an area just below the camera lens feeding into their headset (see the images in the ‘Nature’ article referenced below for details of the set-up). This created the illusion that they were situated behind their own body having their chest rubbed – they could see themselves yet had no sense that their body was actually ‘them’.