Ivan Pavlov (1849–1936) was a Russian physiologist who became famous for his experiments with dogs, in which the animals performed a specific behavior in response to a certain stimulus (see above)—an example of classical conditioning. Although he never thought much of the then fledgling science of psychology, Pavlov’s work on conditioned reflexes has been far reaching, from elementary education to adult training programs. Pavlov was awarded the Nobel Prize in Physiology or Medicine (1904) for his study of the physiology of digestion.

American psychologist B. F. Skinner (1904–1990) extensively studied trial and error learning in animals (later known as operant conditioning). A standard setup for his research involved the following: an animal is placed in a cage (known as a Skinner box; for example, Skinner often used a rat cage) that has a bar or pedal that yields a food reward when pressed. Once the animal has practiced the behavior, it will continue to press the bar repeatedly, having learned to associate this activity with food. By releasing food only when the animal completes some task, the observer can train the subject to perform complex behaviors on demand. These operant conditioning techniques have been used to teach behaviors to various animals, such as training pigeons to play table tennis with their beaks.