Реферат: Computer History Essay Research Paper ABSTRACTCurrent neural

The First Steps

The study of the brain was once limited to the study of living tissue. Any attempts at an

electronic simulation were brushed aside by the neurobiologist community as abstract conceptions

that bore little relationship to reality. This was partially due to the over-excitement in

the 1950?s and 1960?s for networks that could recognize some patterns, but were limited in

their learning abilities because of hardware limitations. In the 1990’s computer simulations

of brain functions are gaining respect as the simulations increase their abilities to predict

the behavior of the nervous system. This respect is illustrated by the fact that many

neurobiologists are increasingly moving toward neural network type simulations. One such

neurobiologist, Sejnowski, introduced a three-layer net which has made some excellent predictions

about how biological systems behave. Figure 2 illustrates this network consisting of three

layers, in which a middle layer of units connects the input and output layers. When the network

is given an input, it sends signals through the middle layer which checks for correct output.

An algorithm used in the middle layer reduces errors by strengthening or weakening connections

in the network. This system, in which the system learns to adapt to the changing conditions,

is called back-propagation. The value of Sejnowski’s network is illustrated by an experiment

by Richard Andersen at the Massachusetts Institute of Technology. Andersen?s team spent years

researching the neurons monkeys use to locate an object in space (Dreyfus and Dreyfus 42-61).

Anderson decided to use a neural network to replicate the findings from their research. They

“trained” the neural network to locate objects by retina and eye position, then observed

the middle layer to see how it responded to the input. The result was nearly identical to what

they found in their experiments with monkeys.

Computer-Synthesized Senses

? Visual Recognition

The ability of a computer to distinguish one customer from another is not yet a reality. But, recent breakthroughs in neural network visual technology are

bringing us closer to the time when computers will positively identify a person.

? Current Research

Studying the retina of the eye is the focus of research by two professors at the California

Institute of Technology, Misha A. Mahowald and Carver Mead. Their objective is to electronically