Biologists studying animal behavior, on the other hand, lacked introspective data and developed an objective methodology, as described by H. S. Jennings (1906)l in his influential work Behavior of the Lower Organisms. Applying this viewpoint to humans, the behaviourism movement, led by John Watson (1878-1958), rejected any theory involving mental processes on the grounds that introspection could not provide reliable evidence. Behaviorist's insisted on studying only objective measures of the percepts (or stiwzulus) given to an1 animal and its resulting actions (or response). Mental constructs such as knowledge, beliefs, goals, and reasoning steps were dismissed as unscientific " folk psychology. " Behaviourism discovered a lot about rats and pigeons, but had less success at understanding humans. Nevertheless, it exerted a strong hold on psychology (especially in the United States) from about I1920 to 1960.
The view of the brain as an information - processing device, which is a principal characteristic of cognitive psychology,
can be traced back at least to the works of William James" (1 842 - 19 10). Helmholtz also insisted that perception involved a form of unconscious logical inference. The cognitive viewpoint was largely eclipsed by behaviourism in the United States, but at Cambridge's Applied Psychology Unit, directed by Frederic Bartlett (1886-1969), cognitive modeling was able to flourish. The Nature of Explanation, by Bartlett's student and successor Kenneth Craik (1943), forcefully reestablished the legitimacy of such " mental " terms as beliefs and goals, arguing that they are just as scientific as, say, using pressure and temperature to talk about gases, despite their being made of molecules that have neither. Craik specified the three key steps of a knowledge - based agent:
(1) the stimulus must be translated into an internal representation.
(2) the representation is manipulated by cognitive processes to derive new internal representations.
(3) these are in turn retranslated.
back into action. He clearly explained why this was a good design for an agent:
If the organism carries a " small - scale model " of external reality and of its own possible actions within its head, it is able to try out various alternatives, conclude which is the best of them, react to future situations before they arise, utilize the knowledge of past events in dealing with the present and future, and in every way to react in a much fuller, safer, and more competent manner to the emergencies which face it. (Craik, 1943) After Craik's death in a bicycle accident in 194.5, his work was continued by Donald Broadbent, whose book Perception and Communication (1958) included some of the first information - processing models of psychological phenomena. Meanwhile, in the United States, the development of computer modeling led to the creation of the field of cognitive science. The field can be said to have started at a workshop in September 1956 at MIT. (We shall see that this is just two months after the conference at which A1 itself was " born. " ) At the workshop, George Miller presented The Magic Number Seven, Noam Chomsky presented Three Models of Language, and Allen Newel1 and Herbert Simon presented The Logic Theory Machine. These three influential papers showed how computer models could be used to address the psychology of memory, language, and logical thinlung, respectively.
It is now a common view among psychologists that " a cognitive theory should be like a computer program " (Anderson, 1980), that is, it should describe a detailed information - processing mecha -
nism whereby some cognitive function might be implemented.
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