Thursday, December 20, 2007

False hand trick

We've been trying to work out the best way of doing this for a while....
We finally hit on this arrangement with a cardigan or jacket to make it easier to trick your brain.

Peter had his real hand under the board, while a false arm was placed on top. Whatever was done to the false hand was done to his real hand underneath the board (with two paint brushes). After a short time the brain transfers the sensation to the fake hand making you believe that its your own hand. It is a very unusual experience - it can even make some people feel sick (the fake hand we used was a Halloween arm covered in blood). When Peter saw the fork hitting the fake hand he reacted as though his own hand had been stabbed.

This seems to work with about 2/3 of the people who do it and relies on the ability of your sight to overcome your proprioception. It illustrates the point that what we think of as our hand consists of a mental map which exists in the brain that is normally mapped to the real physical hand on the end of our arm (full of nerve endings, but with no brain to create the sensation). No-one really feels anything in their body - all the feeling is done in the brain.

Some people can get the same sensation with just a piece of wood in front of them. Imagine believing that the wood was your hand!

The same ideas can be illustrated with the phemomenon of phantom limbs. Brain Story from the BBC is a great series that has some good film of this.

This clip was filmed on a mobile hence the shakey video

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