Figure 1.

Illustration of the ToL disc‐transfer task. The tower configuration consists of three balls placed on three rods of different heights. The start configuration of the balls has to be transformed into a given goal configuration while considering several rules. The major rules for transformation are identical for the two tasks: Only one ball can be moved at once, a ball must not be placed beside a rod, and only the topmost ball of each rod can be moved. The three balls differ in their color and the rods in their length and capacity for holding balls. The left rod can hold up to three balls, the middle rod up to two balls, and the right rod only one ball. Subjects are commonly instructed to solve a given problem in the minimum number of moves. Planning ahead is hence required for efficient problem solving in terms of attaining the optimal solution.