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robotic applications. An assembly-line robot that manipulates auto- mobile parts needs brute strength, not sensitivity, and works perfectly well with powerful arms terminating in pincers rather than fingers and thumb. Universally useful artificial beings, however, need func- tioning fingers-and-thumb hands that include appropriate sensory feedback. A differently shaped or unfeeling hand could not operate electrical switches and valves, or properly use screwdrivers and ham- mers, all of which are designed for the human hand.

A more profound issue is summarized in John Napiers comment a lively hand is the product of a lively mind. . . .When the brain is empty, the hands are still.The inverse might also be truelimited artificial hands might ensure a limited artificial mind because the hands extend the abstract power of the brain into the real world. Even if the brain is made of processed silicon rather than living neurons, the addi- tion of hands turns an isolated artificial intelligence into an interactive artificial being.Such a being could be designed to grow in knowledge and capacity as it explores the world with its questing fingers, just as the human brain has grown through a two-way feedback with the bodys own searching fingers.

Writing in the late 1970s, Napier expressed little hope that an artificial hand could be built. There is nothing comparable to the human hand outside nature,he said,for all our electronic and me- chanical wizardry, we cannot reproduce an artificial forefinger that can feel as well as beckon.Although the human hand is indeed diffi- cult to copy, since Napiers pessimistic statement, we have come a long way toward building robotic and prosthetic hands that work like natural ones. One leading example is under development at NASAs Johnson Space Flight Center in Houston, in conjunction with DARPA. NASA has considerable expertise in building wheeled ro- bots, like the Sojourner rover that explored the Martian surface dur- ing the 1997 Pathfinder mission, but the artificial hand is different. It is the critical part of Robonaut, a robotic astronaut designed to stand in for a human when work must be carried out in space on Earth satellites, or on the International Space Station now taking shape in orbit.

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