Bearing Arms.

June 24, 2009

Merleau-Ponty would be pleased:

Lead researcher Alessandro Farnè first asked volunteers to point at and grab wooden blocks with their hands, then had them perform the same motions with a grabber tool, and finally returned to the hands-only gestures. The researchers recorded all of these tasks using a high-resolution three-dimensional motion-tracking system, so that they could compare in detail the movements performed in each task. They found that after using the grabber, the volunteers approached the blocks with slightly lower acceleration and velocity, although their accuracy was not affected. “They behave like their arm is longer,” says Farnè. “They aren’t clumsy, but they are slower and more determined”.

The effect is subtle, Farnè explains, and wouldn’t cause difficulty with manual tasks. But the experiment was the first to prove definitively that tool use alters a person’s mental representation of his body even after the task is completed. Another experiment on blindfolded volunteers corroborated the findings. After an experimenter touched the participants’ elbow and middle fingertip, they were asked to point using the other hand to those two locations. After a session of using the tool, the participants indicated locations further apart than before tool use: they seemed to perceive the tool-using arm as longer [BBC News].

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