Conditioning is a broad term to describe techniques used by psychologists to study the process of learning.

Psychology has often been defined as the study of behavior. In behavioral psychology, conditioning is the process that states a response (what is known as a reaction) to an object or event (a stimulus or reward) by a person or animal in a given environment, which can be modified (or conditioned) by learning. The theories based on conditioning are generally called stimulus-response (S-R) theories. Thus, behaviorists, those who study behaviorism, believe that behaviors are the result of conditioning.

Beginning in the early twentieth century, American, British, and Russian physiologists, and then later psychologists, began to develop definitions, observations, and procedures about conditioning. As such, physiologists and psychologists have developed a diverse array of methods for studying both human and nonhuman animal activity.

Classical and operant conditioning

Two of the most commonly used techniques are classical conditioning and operant conditioning. They have been used to study the process of learning, one of the key areas of interest to psychologists in the nineteenth-century early days of psychology. Psychologists also attach considerable significance to conditioning because it has been effective in changing human and nonhuman animal behavior in predictable and desirable ways.

Classical conditioning

The Russian physiologist Ivan P. Pavlov (1849– 1936) developed the principles of classical conditioning. In his Nobel Prize–winning research on the digestive processes, he placed meat powder in the mouths of his research animals and recorded their levels of salivation. At one point, he noticed that some of his research animals began to salivate in the absence of food. He reasoned that the presence of the animal caretakers led the animals to anticipate the meat powder, so they began to salivate even without the food.

When classical conditioning occurs, an animal or person initially responds to a naturally occurring stimulus with a natural response (e.g., the food leads to salivation). Then the food is systematically paired with a previously neutral stimulus (e.g., a bell or metronome), one that does not lead to any particular response. With repeated pairings, the natural response occurs when the neutral stimulus appears. The original salivation when food is introduced to the animal (such as a dog) is called the unconditioned response (UR) whereas the food itself is the unconditioned stimulus (US). However, the bell, for example, eventually becomes the conditioned stimulus (CS) and the salivation by the animal upon hearing the bell is the conditioned response (CR).

Pavlovian (i.e., classical) conditioning influenced psychologists greatly, even though Pavlov himself was skeptical of the work psychologists performed. In the United States, John B. Watson (1878–1958), the first widely known behaviorist, used the principles of classical conditioning in his research. For example, in a widely cited study, Watson tried to develop a classically conditioned phobia in an infant.

Operant conditioning

Although classical conditioning became the dominant Russian model for the study of behaviorism, another form of conditioning took hold in the United States. This version, which became known as operant or instrumental conditioning, initially developed from the ideas of the psychologist Edward L. Thorndike (1874– 1949). Thorndike began his psychological research by studying learning in chickens then in cats. Based on the problem solving of these animals, he developed the law of effect, which in simple form states that a behavior that has a positive outcome is likely to be repeated.

Similarly, Thorndike's law of exercise states that the more a response occurs in a given situation, the more strongly it is linked with that situation, and the more likely it is to be repeated in the future. Thorndike's behavioral theories of stimulus (S), organism/ individual (O), and response (R), often abbreviated as S-O-R theories, helped to explain social interactions between individuals and groups of individuals.

Operant conditioning was popularized by the American psychologist Burrhus Frederic Skinner (1904–1990), who is more commonly known as B. F. Skinner. His research and writings influenced not only psychologists but also the public, in general. Operant conditioning differs from classical conditioning in that, whereas classical conditioning relies on an organism's response to some stimulus in the environment, operant conditioning relies on the organism's initiating an action that is followed by some consequence.

For example, when hungry individuals put money into a vending machine, they are rewarded with some product. In psychologists’ terms, the behavior is reinforced; in everyday language, the individuals are satisfied with the outcome. As a result, the next time they are hungry, they are likely to repeat the behavior of putting money into the machine. However, if the machine malfunctions and the individuals get no food, then they are less likely to repeat the behavior in the future. This outcome is called punishment.

Child toilet training.

Child toilet training.
© Maurizio Milanesio/


In 1920, psychologist John B. Watson and his graduate assistant Rosalie Rayner at Johns Hopkins University conducted a series of studies on a baby boy known as Little Albert to study classical conditioning in humans. They published their findings in a paper entitled “Conditioned Emotional Reactions” in the Journal of Experimental Psychology.

The theory of conditioning asserts that all human development and behavior can be boiled down to stimulus and response. Classical conditioning was first used on dogs in the famous experiments of Ivan Pavlov. Watson sought to replicate these experiments in humans to create a fear response of the sort that Watson saw as the root of all phobias in humans. Testing on Little Albert began when he was nine months old.

To start, Watson and Rayner presented Little Albert with various stimuli including burning newspaper, cotton wool, a monkey, a dog, a rabbit, and a white rat. Albert seemed particularly drawn to the white rat. To test the theory of conditioning, Watson struck a metal bar with a hammer next to Albert's head whenever he would touch the white rat. This startled and frightened Little Albert and caused him to cry. Lab notes read as follows: “One of the two experimenters caused the child to turn its head and fixate her moving hand; the other stationed back of the child, struck the steel bar a sharp blow. The child started violently, his breathing was checked and the arms were raised in a characteristic manner. On the second stimulation the same thing occurred, and in addition the lips began to pucker and tremble. On the third stimulation the child broke into a sudden crying fit. This is the first time an emotional situation in the laboratory has produced any fear or even crying in Albert.”

Next they had to test whether this had created a conditioned response in Little Albert. When presented with a rabbit and a dog, Little Albert immediately cried and moved away. This demonstrated that the conditioned fear response indeed persisted. Next the researchers presented the baby with a seal fur coat. This also caused him to cry and attempt to crawl away, and a Santa mask with a white cotton beard also frightened him. He did not show fear or withdrawal, however, when presented with blocks, which he picked up and played with in a normal fashion. Watson concluded from this thatthe conditioned response resulted in Little Albert fearing objects that shared traits with the white rat. This phenomenon is known as generalization. To test whether the conditioned responses would hold or die out in time, they repeated the experiment on Little Albert a month later. They found that he exhibited the same negative responses and withdrawal.

Although Watson asserted that Little Albert was a normal, healthy baby, this has been called into question by numerous experts in recent years. Little Albert died at age six due to causes related to hydrocephalism, and early medical records show that he had received various treatments prior to the Watson studies, including lumbar and cranial punctures to drain some of the cerebrospinal fluid buildup in his brain. Some say this is proof that Albert had some neurological impairment prior to the study, and furthermore that Watson knew about this impairment.

The experiment raised important ethical questions in regards to human experimentation. It was common practice at the time to use poor, ill individuals in experiments, and many have suggested that Little Albert's poor single mother may have felt she had little choice in offering him up for the studies. It is now required to obtain informed consent from all experimental subjects, or from parents or guardians in the case of children. Modern guidelines would not permit a study in which researchers deliberately set out to terrify an infant. Following this experiment and other ethically questionable studies, guidelines were put in place to protect human subjects of clinical studies. Despite their controversial nature, the Little Albert studies are cited widely as important proof of the effects of conditioning and the nature of conditioned responses in humans.

Any time a behavior leads to a positive outcome that is likely to be repeated, psychologists say that behavior has been reinforced. When the behavior leads to a negative outcome, psychologists refer to it as punishment. Two types of reinforcement and punishment have been described: positive and negative.

Positive reinforcement is generally regarded as synonymous with reward: When a behavior appears, something positive results. This leads to a greater likelihood that the behavior will recur. Negative reinforcement involves the termination of an unpleasant situation. Thus, if individuals have a headache, taking some kind of effective pain reliever leads to a satisfying outcome. In the future, when they have a headache, they are likely to take that pain reliever again. In positive and negative reinforcement, some behavior is likely to recur either because something positive results or something unpleasant stops.


—A psychological theory of human development that posits that humans can be trained, or conditioned, to respond in specific ways to specific stimuli and that given the correct stimuli, personalities and behaviors of individuals, and even entire civilizations, can be codified and controlled.
—A type of anxiety disorder most likely characterized by a distinct and persistent fear of a situation or object such as the fear of heights (acrophobia) or enclosed spaces (claustrophobia).
—A medical professional who studies the biological functions of living organisms and their individual parts.

Just as reinforcement comes in two versions, punishment takes two forms. Psychologists have identified positive punishment as the presentation of an unpleasant result when an undesired behavior occurs. By contrast, negative punishment occurs when something positive is removed. In both forms of punishment, an undesired behavior results in a negative consequence. As a result, the undesired behavior is less likely to recur in the future.

Many people mistakenly equate negative reinforcement with punishment because the word negative conveys the idea of punishment. In reality, a situation involving negative reinforcement involves the removal of a negative stimulus, leading to a more satisfying situation. A situation involving punishment always leads to an unwanted outcome.

Nonhuman animals and humans

Beginning with Watson and Skinner, psychology in the United States adopted a behavioral framework in which researchers began to study animals and people through conditioning. From the 1920s through the 1960s, many psychologists performed conditioning experiments with animals with the idea that what was true for nonhuman animals would also be true for humans. Psychologists assumed that the principles of conditioning are universal. Although many of the principles of learning and conditioning developed in nonhuman animal research pertain to human learning and conditioning, psychologists later realized that each species has distinct behavioral characteristics. Consequently, although the principles of conditioning may generalize from nonhuman animals to humans, researchers must consider the differences between species as well.

See also Aversive conditioning ; Classical conditioning ; Operant conditioning .



Nye, Robert D. Three Psychologies: Perspectivesfrom Freud, Skinner, and Rogers, 6th ed. Belmont, CA: Wadsworth, 2000.

Schachtman, Todd, and Steve Reilly, eds. Associative Learning and Conditioning Theory: Human and Nonhuman Applications. London: Oxford University Press, 2011.

Staddon, John E. R. Behaviorism: Mind, Mechanism, and Society. Philadelphia: Psychology Press, 2001.


Psychology Today. “Explaining Behaviorism: Operant & Classical Conditioning.” (accessed July 23, 2015).

University of Washington. “Three Major Types of Learning.” (accessed July 23, 2015).


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