The Tower of London: a study of the effect of problem structure on planning.

Only recently has there been any consideration of the influence of the problem structure on Tower of London task (TOL) performance. Not surprisingly, these few studies that have investigated this issue have found significant differences in the cognitive demands of individual TOL problems. Based on these previous findings, the aim of the current study was to further explore the effects of two problem characteristics on the planning process - namely, goal hierarchy and the number of optimal solution paths. A number of performance measures when solving six-move problems were examined, including preplanning time, movement time, and accuracy. Analysis of the preplanning time revealed that it was significantly affected by goal hierarchy but not the number of solution paths. The individual movement times, however, revealed effects for both goal hierarchy and the number of optimal solution paths. The number of paths only affected movement times at specific moves: those corresponding to the initiation of a subgoal chunk. The results are discussed in terms of the influence of preplanning on subsequent performance. The present study also suggests that greater care be taken in the selection of TOL problems.