Conditioning

Conditioning

Conditioning occurs when an animal's behavior changes as a patterned response to a certain stimulus. The founder of classical conditioning was Ivan Petrovich Pavlov, who devoted more than 30 years to its study. Pavlov began his research career investigating digestion, winning a Nobel prize in 1904 for his work. Pavlov began his signature work on dogs in 1902. He restrained a hungry dog on a stand, and then rang a bell before giving it food. The hungry animal salivated freely in the presence of the food, as would be expected, however Pavlov's dog learned to associate the ringing of the bell with the imminent arrival of the meal and soon could be induced to salivate on hearing the sound alone. Pavlov called the food an unconditional stimulus, because the animal would salivate without fail, or unconditionally, when exposed to it. The ringing of the bell was thus a conditional stimulus, and the animal's learning process was called conditioning.

Pavlov repeated and refined such experiments for many years, using different stimuli and discovering, for example, how the conditioning could be reversed. His work was refined and extended by two American psychologists, Edward L. Thorndike and B.F. Skinner. Thorndike worked with cats, and did many conditioning experiments using a puzzle box. The cat was placed in a wooden box from which it could escape to its waiting food by doing a trick such as pressing a lever or pulling a loop of string. Thorndike observed that the cats would at first wander around the box purposelessly, finally letting themselves out by accident.

After a few trials, the animals learned to do the trick and let themselves out of the box in only a few seconds. B.F. Skinner used a similar idea with his boxes. He placed laboratory rats in boxes that were rigged with a small lever. When the rat pressed the lever, the animal received a food pellet. Skinner also conditioned pigeons to peck at a light in order to receive food. Such conditioning is known as operant conditioning because the animal is rewarded (or punished) for performing a behavior. Once learned, the frequency of the behavior increases (or decreases) with the expectancy of the reward (or punishment).

Conditioning seems to explain more about how laboratory animals learn during laboratory experiments than how animals might act in the wild. Yet more sophisticated experiments in the 1990s have led to tantalizing insights into how the brain works in response to conditioning. So-called expectancy theory tries to explain what the brain believes about the immediate future. Medical researchers in the United States in the late 1980s studied such theories as the helpful effects of placebo drugs, and posited that the brain is organized to work in response to what it assumes will come next, as well as in response to what it actually senses. In the case of placebos, humans are conditioned by the sight of a doctor in a white coat, the prick of a needle, or the smell of antiseptic, for example, to expect to get relief from pain or illness. In many cases, a patient given a placebo improves just as dramatically as a patient given a proven drug because the patient is in some way conditioned to get well. Expectancy theory gained ground in the late 1990s, supported by fascinating research from around the world. Whereas the earliest conditioning experiments studied relatively simple and observable responses to stimuli, researchers in the late 1990s were able to study the brain's chemical reactions and related responses in the immune, endocrine, and hormonal systems.