Planning abilities and the Tower of London: is this task measuring a discrete cognitive function?

The Tower of London (ToL) test is widely used for measuring planning and aspects of problem solving. The primary focus of this study was to asses the relationship among different measures on the ToL. A secondary purpose was to examine the putative relationship between intelligence and working memory with that of ToL performance. Analyses of the interrelation of several ToL parameters indicated that better ToL performance was associated with longer preplanning time and shorter movement execution time. Good performers showed a stronger increase in preplanning duration with task difficulty then intermediate or poor planners. Stepwise multiple regression analysis yield fluid intelligence as the only significant predictor of ToL performance. These result suggest that the Tower of London assesses predominantly planning and problem solving and could not be explained by other cognitive domains.