Mental planning and the Tower of London task

The Tower of London( TOL) task has been used extensively as a test of plann ing ability in neuropsychological patients and normal populations. Particip ants are asked to preplan mentally a sequence of moves to match a start set of discs to a goal, and then to execute the moves one by one. The mental p replanning stage has been identified as critical to efficient performance. The current experiments examined whether manipulations of mental preplannin g influence performance on the TOL. In Experiment 1, the effect of differen t planning instructions was examined. Those told to make full mental plans spent considerably longer in planning than participants given no specific p lanning instructions, yet there was no effect of instruction condition on t he efficiency of executing plans. Experiment 2 investigated whether people were able to plan mentally, by looking at their ability to identify interme diate states of an optimum mental plan. Results indicated that most individ uals could make accurate preplans up to two subgoals ahead, but not three. However, making an efficient preplan did not result in better subsequent ex ecution of moves to solve the TOL trial. It is concluded that people can ma ke effective mental plans for a limited number of moves. However, on the TO L task, mental preplanning does not offer benefits in terms of quicker perf ormance, or more accurate solution. The nature of planning in the TOL task is therefore questioned.