This subsection is concerned with such a task--subjects solving the Tower of Hanoi problem who know a subgoaling strategy. The Tower of Hanoi problem is a useful illustration of the symbolic level also because it makes heavy use of ACT-R's goal structure. Figure 2.3 shows a typical 5-disk tower-of-Hanoi problem. The subject's task is to move the five disks from peg A to peg C. The constraints on the movement of disks are that only one disk can be moved at a time and that a larger disk cannot be placed on a smaller disk. A number of other researchers (e.g., Egan & Greeno, 1974; Karat, 1982) have found that subjects use hierarchical goal structures to solve the Tower of Hanoi problem. With appropriate instructions, one can more or less guarantee that subjects will use hierarchical goal structures to solve the Tower of Hanoi problem. For instance, Ruiz (1987) taught subjects a strategy that involves the following two principles:
(1) The overall goal of solving an n-disk pyramid problem can be accomplished by the subgoals of getting the nth (bottom) disk to the destination peg and then getting the (n-1)-disk pyramid into the destination peg.
(2) To get the nth disk to a peg, one tries to get the largest disk blocking its move out of the way. This second rule can recurse in that to move this blocking disk requires moving yet other disks.
ACT-R Model
Microsoft Excel Spreadsheet of Model