Allen Newell:

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Newell divides cognition into several levels. The program level represents and manipulates the world in the form of symbols. The knowledge level is built on top of the symbolic level and is the level of rational agents: an agent has a body of knowledge, some goals to achieve and some actions that it can perform. An agent's behavior is determined by the "principle of rationality": the agent performs those actions that, on the basis of the knowledge it has, bring it closer to the goals.
General intelligent behavior requires symbol-level systems and knowledge-level systems.
Newell then broadens his division of cognitive levels by including physical and biological states. The whole band can be divided into four bands: neural, cognitive, rational and social. The cognitive band can be divided based on the response times: at the memory level the response time (the time required to retrieve the referent of a symbol) is about ten milliseconds; at the decision level the response time is 100 milliseconds (the time required to manipulate knowledge), at the compositional level is one second (time required to build actions), a tthe execution level ten seconds (time required to perform the action).
In the rational band the system appears as a goal-driven organism, capable of processing knowledge and of exhibiting adaptive behavior.
Newell surveys a number of cognitive theories and cognitive architectures, particularly SOAR, which is offered as a candidate for a unified theory of cognition.

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