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[E]ach of the [robots] behaviors independently tries to find out (i) whether it is relevant (i. e. whether it is at all correlated to positive feedback) and (ii) what the conditions are under which it becomes reliable (i.e. the con- ditions under which it maximizes the probability of receiving positive feedback and minimizes the probability of receiving negative feedback).

Positiveand negativefeedback mean that the signals to the leg motors are modified to enhance or diminish the occurrence of spe- cific motions, depending on whether they contribute to the goal of walkinga process similar in spirit to biological evolution, which by trial and error weeds out whatever does not contribute to an organisms survival. Little by little, the six legs coordinated themselves and Genghis became a sophisticated walker.The result is a robot that behaves in a lifelike manner as it crawls on the floor and over ob- stacles, and follows a human around the room when its heat sensors detect one.

In a top-down approach, a robots actions are motivated by the expectations that are part of the symbolic model of the world that is built into it; but Genghis gained the intelligence to walk by respond- ing directly to stimuli, an approach often called bottom-up. Both the top-down and bottom-up methods are valuable in constructing arti- ficial minds even if they lack bodies, but it is easy to see that the latter approach is especially meaningful for a robot that physically interacts with the real world.An autonomous robot is not useful unless it deals intelligently with its physical environment, where it has to move with- out collisions, manipulate objects without breaking them, and so on. If the right learning mechanisms could be found, that interaction would constantly help the robotic brain develop on the basis of expe- rience, just as we humans learn to function in the world by doing things in it.

Brookss approach was one new thread in AI that began in the mid-1980s; it was not the only one. In 1986, Marvin Minsky pre- sented an alternate approach in his book The Society of Mind. Rather than consider the human mind as a single entity responsible for all thought and behavior, which could in principle be described once and for all, he proposed that different components of the brain all speakat the same time. From this babble, in which some voices are

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