 Wertheimer's long-awaited book on mathematical problem-solving, "Productive Thinking," was published posthumously in 1945, but Köhler was left to guide the movement without his two long-time colleagues.Gestalt psychology should not be confused with the Gestalt therapy, which is only peripherally linked to Gestalt psychology.The founders of Gestalt therapy, Fritz and Laura Perls, had worked with Kurt Goldstein, a neurologist who had applied principles of Gestalt psychology to the functioning of the organism.