ABSTRACT
Our society depends a great deal on information processing machines. These are communication and decision systems whose main purpose is to send descriptions of situations from one place to another. The idea can be illustrated by examining the difference between a telephone line and a railroad line. A telephone line is used to transmit messages while a railroad line transmits physical objects. One of the insights of the 1950-1960 decade was that the concepts used to describe external information processing systems, such as a telephone system, can also be applied to understanding human perception and cognition.
