Cognitive Science: Definition, Status, and Questions

Abstract

conceptual structures. Finer grain sizes are appropriate if the task to be modeled is an elementary one. Just & Carpenter's ( 1985) production model of the rotation of mental images is a good example of this approach. The productions Just's & Carpenter's program contained primitive actions such as focusing attention on parts of a visual image and making slight movements of the fixated image in the mind's eye. There are three parts to a production-executing machine: a pattern recogni­ tion system that compares the pattern parts of productions to structures working memory, a set of primitive actions that can be associated with a pattern, and a conflict resolution rule that determines which production is to be executed when two or more productions match the working-memory structure. Production system modeling puts the burden of problem solving upon the pattern recognition system. It is fairly easy to assemble a list of symbol manipulating actions that are sufficient to solve a problem if they are done at the appropriate time. The difficulty is stating the rules that determine when an action will be taken. Production-executing machines mix serial and parallel operations. The machines are parallel the sense that all production patterns are sensed simultaneously, so that the number of production rules long-term memory does not slow down the conceptual machines' operation. 6 The machines operate series the sense that any communication from production to production that takes place via changes the working-memory structures must be a serial operation. Production Systems as Models of Psychological Processes Several different production system architectures have been proposed as psychological models (Anderson 1983; Holland et a1 1 986; Hunt & Lansman 1986). They differ largely the assumptions they make about (a) the number of working-memory subsystems that can operate parallel and (b) the notations used to code information within each subsystem. The syntactical structures of the systems' mentalese vary from Anderson's use of proposition­ al calculus notation to Hunt & Lansman's use of feature lists and the use of image-like codes by Holland et al and Kosslyn (1980). Since the 6If a production system is simulated on a conventional (serial) computer the number of productions the system does affect the program's speed. This is of no conceptual significance.