The functional architecture of cognition

This view is often expressed by saying that the the neurophysiological hardware of the brain implements a ``cognitive processor'', a simple symbol-manipulating machine, and that this is a production system. For a statement of this view, see Foundations of Cognitive Science edited by Posner (Springer-Verlag 1989; PSY BH:P 084), Chapter 3. For what Newell and Simon believed to be the eight main architectural features of the mind, see Computer Models of Mind by Boden (CUP 1988; PSY KD:B 063), page 164.

But there can be many different types of production system. Here's a list of some of the ways they could differ:

1. The symbols allowed - what, and how many?
2. The resolution methods.
3. The capacity of STM. Is there a maximum size, and if so, what happens when more symbols are added? Do old ones drop out? If so, how does this depend on the time they were added? Is there any kind of ``chunking'' mechanism, so that symbols can be grouped into a single slot?
4. The rules' conditions. Can these test perceptual data directly, or must they go via STM? What is the maximum size of pattern you can have? Can you have ``wild card'' patterns - so that _ for example, might match any set of symbols starting with and ending in . Can the conditions check how many of some symbol there are?
5. The rule's actions. Can these generate actions directly, or must these go via STM? How many symbols can they add? Can they delete symbols?

Different theorists have proposed different types of cognitive processor. The ways in which one differs from another: the complexity of its rules, the capacity of STM and so on, these define its functional architecture. In the same way, a VAX, a PC, and an Apple Mac are all computers, with the same general design. But the details of their functional architecture - the maximum size of number that can be stored, the memory capacity, and so on - are all different.