Knowledge Representation

The function of this chapter is to specify how knowledge is represented in ACT–R. However, to do this, we also need to specify something about how ACT–R processes this knowledge. The process assumptions in ACT–R can be organized according to the 2×2×2 system illustrated in Table 2.1. There are assumptions about how the system performs and how the system learns. Within each topic, one can distinguish between assumptions that are relevant to declarative memory and assumptions that are relevant to procedural memory. One can further divide the assumptions according to whether they apply to ACT–R at the symbolic level or at the subsymbolic level. This and the next two chapters discuss all aspects of the theory (i.e., all eight cells in Table 2.1). Table 2.1 indicates where each aspect of the theory is discussed. Table 2.1 also indicates the units in the ACT–R Web tutorial that correspond to these topics. This Web tutorial can be accessed by following the tutorial link from the ACT–R Web site https://act.psy.cmu.edu. In our ACT–R classes, we typically devote 1 week to each tutorial unit. There are nine tutorial units. Students appear to require all 9 weeks (at 5–10 hours per week) to come to mastery of the material. So a word to the wise: The material in these chapters is not to be taken lightly. Table 2.1 Process Assumptions of the ACT–R Theory

Performance
	Declarative	Procedural
Symbol	Chapter 2	Chapter 2
	Tutorial Units 1 & 2	Tutorial Units 1 & 2
Subsymbolic	Chapter 3	Chapter 3
	Tutorial Units 4 & 5	Tutorial Unit 3

Learning
	Declarative	Procedural
Symbol	Chapter 4–5	Chapter 4
	Throughout	Tutorial Unit 8
Subsymbolic	Chapter 4	Chapter 4
	Tutorial Unit 6	Tutorial Unit 7