Psychologist Edward L. Thorndike (1874–1949) was the first scientist to systematically study operant conditioning. In his research Thorndike (1898) 1 observed cats who had been placed in a “puzzle box” from which they tried to escape (Note Video Clip: Thorndike’s Puzzle Box). At first the cats scratched, bit, and swatted haphazardly, without any idea of how to get out. But eventually, and accidentally, they pressed the lever that opened the door and exited to their prize, a scrap of fish. The next time the cat was constrained within the box it attempted fewer of the ineffective responses before carrying out the successful escape, and after several trials the cat learned to almost immediately make the correct response.
Observing these changes in the cats’ behavior led Thorndike to develop hislaw of effect, the principlethat responses that createa typicallypleasant outcomein a particular situation are more likely to occur again in a similar situation,whereas responses that produce a typically unpleasant outcome are less likely to occur again in the situation (Thorndike, 1911). 2 The essence of the law of effect is that successful responses, because they are pleasurable, are “stamped in” by experience and thus occur more frequently. Unsuccessful responses, which produce unpleasant experiences, are “stamped out” and subsequently occur less frequently.