Why you can't tickle yourself: what your brain knows that your skin does not
Can a robot help you tickle yourself?
Your brain forecasts the touch of your own hand, and a forecast can be wrong. In 1999, a London lab built a robot to make it wrong on purpose, by small, exact amounts.
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Rono is not sure: "A forecast? Then show me a way to fool it." Miva knows a test that did just that. Sarah-Jayne Blakemore, a scientist in London, set up a test with robots. Your left hand moves a handle, and a robot arm copies the move with soft foam on your right palm.
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When the robot copies your move at once and in the same direction, the forecast fits. The touch is turned down, and it is only a touch.
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Then she makes the robot change the direction. Your hand moves forward and back, but the foam strokes your palm from side to side. The forecast no longer fits, and your own move tickles you.
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Waiting works too. When the robot waits a fifth of a second, the touch comes late, and it tickles more. Most people did not even notice the wait.
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The bigger the gap between the forecast and the touch, the more it tickles. So the question was never only whose hand it is. It is whether your brain saw the touch coming.
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Rono yawns: so what? His brain turns down his own touch, and that seems harmless. Miva holds up one finger. She says she can show him in two minutes where it is not harmless at all.
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Quick check
The same robot. Your left hand stays still, and a friend moves the handle.
Show the answer
Yes. Your brain gave no order, so it made no forecast, and nothing turns the touch down.
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Go further
Two surprising tests.