Gestalt psychology
Gestalt psychologists were the first to study problem solving in humans and apes. Wolfgang Kohler showed that chimpanzees could solve problems by thought alone; Max Wertheimer studied how diagrams helped students solve geometry problems, and Karl Duncker studied general problem-solving. Generally, both Wertheimer and Duncker preferred the broader term 'productive thinking' to 'problem solving', but it is not used much now.