In one very striking illusion, you can become convinced that you can feel a rubber hand being touched just as if it were your own. To find out for yourself, ask a friend to sit across from you at a small table. Use blocks or coffee cups to prop up a vertical partition on the table, as shown in the illustration on the preceding page. A flat piece of cardboard will do. Rest your right hand behind the partition, so you cannot see it. Then, in view beside the partition, place a plastic right hand--the kind you can buy from a novelty shop or a party store around Halloween. Ask your assistant to repeatedly tap and stroke your concealed right hand in a random sequence. Tap, tap, tap, stroke, tap, stroke, stroke. At the same time, while you watch, he must also tap and stroke the visible dummy in perfect synchrony.

If he continues the procedure for about 20 or 30 seconds, something quite spooky will happen: you will have an uncanny feeling that you are actually being stroked on the fake hand. The sensations will seem to emerge directly from the plastic rather than from your actual hidden flesh.

This article was originally published with the title The Phantom Hand.

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