The more time scientists spend designing computers, the more they marvel at the human brain. Tasks that stump the most advanced supercomputer--recognizing a face, reading a handwritten note--are child's play for the 3-lb. organ. Most important, unlike any conventional computer, the brain can learn from its mistakes. Researchers have tried for years to program computers to imitate the brain's abilities, but without success. Now a growing number of designers believe they have the answer: if a computer is to function more like a person and less like an over-grown calculator, it must be built more like a brain, which distributes information across a vast interconnected web of nerve cells, or neurons. Conventional computers function by following a chainlike sequence of detailed instructions. Although very fast, their processors can perform. only one task at a time. This approach works best in solving problems that can be broken down into simpler logical pieces. The processors in a neural-network computer, by contrast, form. a grid much like the nerve cells in the brain. Since these artificial neurons are interconnected, they can share information and perform. tasks at the same time. This two-dimensional approach works best at recognizing patterns. Instead of programming a neural-network computer to make decisions, its maker trains it to recognize the patterns in any solution to a problem by repeatedly feeding examples to the machine. This process is like a process that prepares all possible moves in a chess game and try to find a best approach to it. If the examples are not sufficient or complete, the computer will be in for trouble, after all, it can not respond to something it can not recognize as a pattern in its memory. Neural networks come in all shapes and size. The new networks will make things which were simply impossible completely feasible in the near future. What the users need to do is to wait and see. Developers are experimenting with new equipment and hopefully they will succeed. Until now most existed as software simulations because redesigning computer chips took a lot of time and money. By experimenting with different approaches through software rather than hardware, scientists have been able to avoid costly mistakes. What does the word 'stump' in paragraph 1, line 2, mean?