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loud and others soft, some agree and some oppose each other, a con- sensus emerges that defines behavior.

The idea of distributed and even contending voiceswithin the human mind might seem strange. Minskys model is only one among many proposed since the time of Descartes, as we consider how the physical brain and conscious mind are linked to each other, and is far from being accepted as a definitive explanation of how the mind works.But used as an AI technique, the concept of multiple voices has imparted convincingly lifelike behavior to various robotic toys.

Along with such changes in the design of artificial brains, en- hancements in computer speed and capacity offered new possibilities for AI. One advance was the technique of parallel processing, which some observers considered a fifth generation in computing (the fourth generation consisting of computers using VLSI and ULSI technol- ogy). In a parallel processor, many computer chips are interconnected so that each one handles a different part of a problem at the same time, which can give impressive results. In 1987, for instance, a parallel processor called the Connection Machine operated 64,000 micropro- cessors simultaneously to perform two billion computer operations per secondan impressively high speed that could hardly be matched by conventional computers at the time. But programming a parallel machine so that the parts of the problem are properly parceled out is difficult, and it is unclear whether parallel processing can offer enor- mous advantages.

However, the idea of carrying out many thoughtoperations at the same time is promising for AI because thats how the human brain works. Each of its many billions of neurons is intricately connected with others through upward of a thousand connecting points, called synapses. The neural signals that define the brains operations travel through the network. Many neural events are going on at the same time, a huge benefit for processing speed. The multiply connected neural architecture also protects a brain that is partly damaged from necessarily losing an entire function such as memory, and allows re- placement neural connections to be forged so that new areas can take over from damaged ones. In fact, the process of learning seems to

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