Creating the Illusion
You don't need laboratory resources to carry out the startling (and a wee bit disturbing) trick on the brain. What you do need is the following:
- A realistic-looking rubber hand (Stores selling costumes or magic supplies will have them.)
- A table and chair
- A towel
- A cardboard panel (a side cut from a cardboard box is fine) to use as a divider, attached to some sort of base that allows it to stand upright.
- A subject
- A helper
Sit your subject on the chair with one arm, let's say the right one, extended and resting on the table. Position your divider as close as possible to the subject's left shoulder, and then move the subject's left arm to the other side of it, so she can't see it, but with the hand still on the table. Drape a towel over her left shoulder and down onto the table in front of her. At the end of the towel, place the rubber hand approximately where her actual hand would be if it were her own arm under the towel.
This last part is important. The illusion works best when the position of the rubber hand is realistic.
Now, the trick: You and your helper simultaneously stroke a hand -- one of you the left, hidden hand, and the other the visible, rubber hand. The strokes should be as closely matched as possible. Your subject should be watching the rubber hand being stroked.
Within seconds (the average was 11 in a 2004 study at University College London), your subject will likely feel like the rubber hand is her own hand -- that it is part of her physical self, the body she owns [source: Science Daily]. Show knows, intellectually, it isn't; but her brain is telling her different. Her brain has determined that she owns the rubber hand.
In the lab, researchers do have the advantage of access to fMRI, or functional magnetic resonance imaging, which measures activity in various areas of the brain in real-time. In 2004, scientists discovered that when the illusion took hold, one specific area lit up, revealing excitingly concrete evidence of what, exactly, is going on here.