How tools become part of the body

When admiring a brilliant sportsman or woman, commentators often describe a wielded tennis racquet, cricket bat or other sporting appendage, as having become like an extension of the athlete's own body, so fluid and deft is their control of the lump of metal or wood. It's a metaphor we should be able to relate to, since all of us, champion athlete or not, absorb tools into our inner representation of our own bodies - what cognitive psychologists call our "body schema".

That's according to Lucilla Cardinali and colleagues who demonstrated this graphically in a new study in which participants reached with their hand for a small block, both before and after using a 40-cm long grasping device (similar to those used for picking up rubbish) to reach for the same block.

After several minutes using the grasping tool, the participants subsequent reaching movements with their hand were slower to start and stop, making them longer-lasting overall, compared with before the tool use - as if their own arm was now perceived as longer. Moreover, when the participants were subsequently blindfolded and asked to point to where they'd just been touched by the researchers, on the tip of the middle finger and on the elbow, the places the participants pointed to were further apart, compared with before tool use, again suggesting that they now perceived their arm to be longer.

These effects lasted for at least 15 minutes after tool use, but the researchers haven't yet tested the duration of the effects systematically.

Psychologists have known for some time that our representation of our bodies must be dynamic. You can't get to where you want to go without knowing where you are to start with, so before moving the limbs, the brain and spinal cord need to know the limbs' current location. What's more, the force needed to perform an action appropriately depends on the length of the muscles, which is also affected by the position of the limbs. There are also changes to the body brought about by growing, ageing and injury that must be accommodated for accurate movement control. Given this adaptability it should perhaps come as no surprise that tools can be seamlessly and rapidly incorporated into the body schema.

Lead author Lucilla Cardinali told the Digest that her lab are currently exploring whether expertise affects the way tools are incorporated, such as when a tennis player wields a racquet.
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Cardinali, L., Frassinetti, F., Brozzoli, C., Urquizar, C., Roy, A., & Farnè, A. (2009). Tool-use induces morphological updating of the body schema. Current Biology, 19 (12) DOI: 10.1016/j.cub.2009.05.009

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