Tool use can alter people's perception of the size and position of their body parts.
INSERM's Alessandro Farnè and Lucilla Cardinali at Claude Bernard University in Lyon, France, and their colleagues had volunteers use a mechanical grabbing arm (pictured right) that extends reach by 40 centimetres. Measuring arm movements with a high-resolution motion-tracking system, they showed that the volunteers reduced the velocity and acceleration of movements to grab or point at an object after a period of using the tool.
When blindfolded, the volunteers also estimated their arms to be slightly longer after tool use, confirming a long-held hypothesis that body schema — the sense of where one's body parts are in space — is plastic.
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For a longer story on this research, see http://tinyurl.com/mwjpow.