Lasting reductions in illegal moves following an increase in their cost: evidence from river-crossing problems

The authors present 3 experiments demonstrating ways to reduce illegal moves in problem-solving tasks. They propose a 3-stage framework for the rejection of illegal moves. An illegal move must come to mind and be selected, checked for legality, and correctly rejected. Illegal move reduction can occur at any stage. Control group participants benefited from solving the same problem twice but failed to show transfer to an isomorph, replicating results from S. K. Reed, G. W. Ernst, and R. Banerji (1974). Participants who were penalized for making illegal moves showed reductions in illegal moves even when solving a novel isomorph without penalty. The authors propose that illegal move reduction occurs when solvers are cautious and check moves for legality frequently.