in pavlov's original experiment the conditioned stimulus (cs) was the

Classical Conditioning

Learning objectives.

• Explain how classical conditioning occurs
• Identify the NS, UCS, UCR, CS, and CR in classical conditioning situations

Does the name Ivan Pavlov ring a bell? Even if you are new to the study of psychology, chances are that you have heard of Pavlov and his famous dogs.

Pavlov (1849–1936), a Russian scientist, performed extensive research on dogs and is best known for his experiments in classical conditioning (Figure 1). As we discussed briefly in the previous section, classical conditioning is a process by which we learn to associate stimuli and, consequently, to anticipate events.

Figure 1 . Ivan Pavlov’s research on the digestive system of dogs unexpectedly led to his discovery of the learning process now known as classical conditioning.

Pavlov came to his conclusions about how learning occurs completely by accident. Pavlov was a physiologist, not a psychologist. Physiologists study the life processes of organisms, from the molecular level to the level of cells, organ systems, and entire organisms. Pavlov’s area of interest was the digestive system (Hunt, 2007). In his studies with dogs, Pavlov measured the amount of saliva produced in response to various foods. Over time, Pavlov (1927) observed that the dogs began to salivate not only at the taste of food, but also at the sight of food, at the sight of an empty food bowl, and even at the sound of the laboratory assistants’ footsteps. Salivating to food in the mouth is reflexive, so no learning is involved. However, dogs don’t naturally salivate at the sight of an empty bowl or the sound of footsteps.

These unusual responses intrigued Pavlov, and he wondered what accounted for what he called the dogs’ “psychic secretions” (Pavlov, 1927). To explore this phenomenon in an objective manner, Pavlov designed a series of carefully controlled experiments to see which stimuli would cause the dogs to salivate. He was able to train the dogs to salivate in response to stimuli that clearly had nothing to do with food, such as the sound of a bell, a light, and a touch on the leg. Through his experiments, Pavlov realized that an organism has two types of responses to its environment: (1) unconditioned (unlearned) responses, or reflexes, and (2) conditioned (learned) responses.

In Pavlov’s experiments, the dogs salivated each time meat powder was presented to them. The meat powder in this situation was an unconditioned stimulus (UCS) : a stimulus that elicits a reflexive response in an organism. The dogs’ salivation was an unconditioned response (UCR) : a natural (unlearned) reaction to a given stimulus. Before conditioning, think of the dogs’ stimulus and response like this:

In classical conditioning, a neutral stimulus is presented immediately before an unconditioned stimulus. Pavlov would sound a tone (like ringing a bell) and then give the dogs the meat powder (Figure 2). The tone was the neutral stimulus (NS), which is a stimulus that does not naturally elicit a response. Prior to conditioning, the dogs did not salivate when they just heard the tone because the tone had no association for the dogs. Quite simply this pairing means:

When Pavlov paired the tone with the meat powder over and over again, the previously neutral stimulus (the tone) also began to elicit salivation from the dogs. Thus, the neutral stimulus became the conditioned stimulus (CS) , which is a stimulus that elicits a response after repeatedly being paired with an unconditioned stimulus. Eventually, the dogs began to salivate to the tone alone, just as they previously had salivated at the sound of the assistants’ footsteps. The behavior caused by the conditioned stimulus is called the conditioned response (CR) . In the case of Pavlov’s dogs, they had learned to associate the tone (CS) with being fed, and they began to salivate (CR) in anticipation of food.

Figure 2 . Before conditioning, an unconditioned stimulus (food) produces an unconditioned response (salivation), and a neutral stimulus (bell) does not produce a response. During conditioning, the unconditioned stimulus (food) is presented repeatedly just after the presentation of the neutral stimulus (bell). After conditioning, the neutral stimulus alone produces a conditioned response (salivation), thus becoming a conditioned stimulus.

View the following video to learn more about Pavlov and his dogs:

You can view the transcript for “Classical Conditioning – Ivan Pavlov” here (opens in new window) .

Real World Application of Classical Conditioning

How does classical conditioning work in the real world? Consider the case of Moisha, who was diagnosed with cancer. When she received her first chemotherapy treatment, she vomited shortly after the chemicals were injected. In fact, every trip to the doctor for chemotherapy treatment shortly after the drugs were injected, she vomited. Moisha’s treatment was a success and her cancer went into remission. Now, when she visits her oncologist’s office every 6 months for a check-up, she becomes nauseous. In this case, the chemotherapy drugs are the unconditioned stimulus (UCS), vomiting is the unconditioned response (UCR), the doctor’s office is the conditioned stimulus (CS) after being paired with the UCS, and nausea is the conditioned response (CR). Let’s assume that the chemotherapy drugs that Moisha takes are given through a syringe injection. After entering the doctor’s office, Moisha sees a syringe, and then gets her medication. In addition to the doctor’s office, Moisha will learn to associate the syringe with the medication and will respond to syringes with nausea. This is an example of higher-order (or second-order) conditioning, when the conditioned stimulus (the doctor’s office) serves to condition another stimulus (the syringe). It is hard to achieve anything above second-order conditioning. For example, if someone rang a bell every time Moisha received a syringe injection of chemotherapy drugs in the doctor’s office, Moisha likely will never get sick in response to the bell.

Consider another example of classical conditioning. Let’s say you have a cat named Tiger, who is quite spoiled. You keep her food in a separate cabinet, and you also have a special electric can opener that you use only to open cans of cat food. For every meal, Tiger hears the distinctive sound of the electric can opener (“zzhzhz”) and then gets her food. Tiger quickly learns that when she hears “zzhzhz” she is about to get fed. What do you think Tiger does when she hears the electric can opener? She will likely get excited and run to where you are preparing her food. This is an example of classical conditioning. In this case, what are the UCS, CS, UCR, and CR?

What if the cabinet holding Tiger’s food becomes squeaky? In that case, Tiger hears “squeak” (the cabinet), “zzhzhz” (the electric can opener), and then she gets her food. Tiger will learn to get excited when she hears the “squeak” of the cabinet. Pairing a new neutral stimulus (“squeak”) with the conditioned stimulus (“zzhzhz”) is called higher-order conditioning, or second-order conditioning. This means you are using the conditioned stimulus of the can opener to condition another stimulus: the squeaky cabinet (Figure 3). It is hard to achieve anything above second-order conditioning. For example, if you ring a bell, open the cabinet (“squeak”), use the can opener (“zzhzhz”), and then feed Tiger, Tiger will likely never get excited when hearing the bell alone.

Figure 3 . In higher-order conditioning, an established conditioned stimulus is paired with a new neutral stimulus (the second-order stimulus), so that eventually the new stimulus also elicits the conditioned response, without the initial conditioned stimulus being presented.

Everyday Connection: Classical Conditioning at Stingray City

Figure 4 . Kate holds a southern stingray at Stingray City in the Cayman Islands. These stingrays have been classically conditioned to associate the sound of a boat motor with food provided by tourists. (credit: Kathryn Dumper)

Kate and her husband Scott recently vacationed in the Cayman Islands, and booked a boat tour to Stingray City, where they could feed and swim with the southern stingrays. The boat captain explained how the normally solitary stingrays have become accustomed to interacting with humans. About 40 years ago, fishermen began to clean fish and conch (unconditioned stimulus) at a particular sandbar near a barrier reef, and large numbers of stingrays would swim in to eat (unconditioned response) what the fishermen threw into the water; this continued for years. By the late 1980s, word of the large group of stingrays spread among scuba divers, who then started feeding them by hand. Over time, the southern stingrays in the area were classically conditioned much like Pavlov’s dogs. When they hear the sound of a boat engine (neutral stimulus that becomes a conditioned stimulus), they know that they will get to eat (conditioned response).

As soon as Kate and Scott reached Stingray City, over two dozen stingrays surrounded their tour boat. The couple slipped into the water with bags of squid, the stingrays’ favorite treat. The swarm of stingrays bumped and rubbed up against their legs like hungry cats (Figure 4). Kate and Scott were able to feed, pet, and even kiss (for luck) these amazing creatures. Then all the squid was gone, and so were the stingrays.

Classical conditioning also applies to humans, even babies. For example, Sara buys formula in blue canisters for her six-month-old daughter, Angelina. Whenever Sara takes out a formula container, Angelina gets excited, tries to reach toward the food, and most likely salivates. Why does Angelina get excited when she sees the formula canister? What are the UCS, CS, UCR, and CR here?

So far, all of the examples have involved food, but classical conditioning extends beyond the basic need to be fed. Consider our earlier example of a dog whose owners install an invisible electric dog fence. A small electrical shock (unconditioned stimulus) elicits discomfort (unconditioned response). When the unconditioned stimulus (shock) is paired with a neutral stimulus (the edge of a yard), the dog associates the discomfort (unconditioned response) with the edge of the yard (conditioned stimulus) and stays within the set boundaries.

For a humorous look at conditioning, you can watch an example from the television show  The Office . Jim conducts an experiment in which he offers Dwight a breath mint every time Jim’s computer makes a specific sound. After repeating this several times, he eventually conditions Dwight to automatically expect a breath mint upon hearing that sound.   See if you can identify the NS, UCS, UCR, CS, and CR.

Review the classical conditioning concepts yet again by walking through Pavlov’s research in the following interactive:

Think It Over

Can you think of an example in your life of how classical conditioning has produced a positive emotional response, such as happiness or excitement? How about a negative emotional response, such as fear, anxiety, or anger?

• Modification and adaptation, addition of tutorial. Provided by : Lumen Learning. License : CC BY: Attribution
• Classical conditioning interactive. Authored by : Jessica Traylor for Lumen Learning. Provided by : Lumen Learning. License : CC BY: Attribution
• Classical Conditioning. Authored by : OpenStax College. Located at : https://openstax.org/books/psychology-2e/pages/6-2-classical-conditioning . License : CC BY: Attribution . License Terms : Download for free at https://openstax.org/books/psychology-2e/pages/1-introduction
• Classical Conditioning - Ivan Pavlov. Authored by : BullyingNewsVideos. Located at : https://www.youtube.com/watch?v=hhqumfpxuzI . License : Other . License Terms : Standard YouTube License
• The Office Classical Conditioning. Authored by : Susann Stanley. Provided by : Vimeo. Located at : https://vimeo.com/35754924 . License : All Rights Reserved

6.2 Classical Conditioning

Learning objectives.

By the end of this section, you will be able to:

• Explain how classical conditioning occurs
• Summarize the processes of acquisition, extinction, spontaneous recovery, generalization, and discrimination

Does the name Ivan Pavlov ring a bell? Even if you are new to the study of psychology, chances are that you have heard of Pavlov and his famous dogs.

Pavlov (1849–1936), a Russian scientist, performed extensive research on dogs and is best known for his experiments in classical conditioning ( Figure 6.3 ). As we discussed briefly in the previous section, classical conditioning is a process by which we learn to associate stimuli and, consequently, to anticipate events.

Pavlov came to his conclusions about how learning occurs completely by accident. Pavlov was a physiologist, not a psychologist. Physiologists study the life processes of organisms, from the molecular level to the level of cells, organ systems, and entire organisms. Pavlov’s area of interest was the digestive system (Hunt, 2007). In his studies with dogs, Pavlov measured the amount of saliva produced in response to various foods. Over time, Pavlov (1927) observed that the dogs began to salivate not only at the taste of food, but also at the sight of food, at the sight of an empty food bowl, and even at the sound of the laboratory assistants' footsteps. Salivating to food in the mouth is reflexive, so no learning is involved. However, dogs don’t naturally salivate at the sight of an empty bowl or the sound of footsteps.

These unusual responses intrigued Pavlov, and he wondered what accounted for what he called the dogs' “psychic secretions” (Pavlov, 1927). To explore this phenomenon in an objective manner, Pavlov designed a series of carefully controlled experiments to see which stimuli would cause the dogs to salivate. He was able to train the dogs to salivate in response to stimuli that clearly had nothing to do with food, such as the sound of a bell, a light, and a touch on the leg. Through his experiments, Pavlov realized that an organism has two types of responses to its environment: (1) unconditioned (unlearned) responses, or reflexes, and (2) conditioned (learned) responses.

In Pavlov’s experiments, the dogs salivated each time meat powder was presented to them. The meat powder in this situation was an unconditioned stimulus (UCS) : a stimulus that elicits a reflexive response in an organism. The dogs’ salivation was an unconditioned response (UCR) : a natural (unlearned) reaction to a given stimulus. Before conditioning, think of the dogs’ stimulus and response like this:

In classical conditioning, a neutral stimulus is presented immediately before an unconditioned stimulus. Pavlov would sound a tone (like ringing a bell) and then give the dogs the meat powder ( Figure 6.4 ). The tone was the neutral stimulus (NS) , which is a stimulus that does not naturally elicit a response. Prior to conditioning, the dogs did not salivate when they just heard the tone because the tone had no association for the dogs.

When Pavlov paired the tone with the meat powder over and over again, the previously neutral stimulus (the tone) also began to elicit salivation from the dogs. Thus, the neutral stimulus became the conditioned stimulus (CS) , which is a stimulus that elicits a response after repeatedly being paired with an unconditioned stimulus. Eventually, the dogs began to salivate to the tone alone, just as they previously had salivated at the sound of the assistants’ footsteps. The behavior caused by the conditioned stimulus is called the conditioned response (CR) . In the case of Pavlov’s dogs, they had learned to associate the tone (CS) with being fed, and they began to salivate (CR) in anticipation of food.

Link to Learning

View this video about Pavlov and his dogs to learn more.

Real World Application of Classical Conditioning

How does classical conditioning work in the real world? Consider the case of Moisha, who was diagnosed with cancer. When she received her first chemotherapy treatment, she vomited shortly after the chemicals were injected. In fact, every trip to the doctor for chemotherapy treatment shortly after the drugs were injected, she vomited. Moisha’s treatment was a success and her cancer went into remission. Now, when she visits her oncologist's office every 6 months for a check-up, she becomes nauseous. In this case, the chemotherapy drugs are the unconditioned stimulus (UCS), vomiting is the unconditioned response (UCR), the doctor’s office is the conditioned stimulus (CS) after being paired with the UCS, and nausea is the conditioned response (CR). Let's assume that the chemotherapy drugs that Moisha takes are given through a syringe injection. After entering the doctor's office, Moisha sees a syringe, and then gets her medication. In addition to the doctor's office, Moisha will learn to associate the syringe with the medication and will respond to syringes with nausea. This is an example of higher-order (or second-order) conditioning, when the conditioned stimulus (the doctor's office) serves to condition another stimulus (the syringe). It is hard to achieve anything above second-order conditioning. For example, if someone rang a bell every time Moisha received a syringe injection of chemotherapy drugs in the doctor's office, Moisha likely will never get sick in response to the bell.

Consider another example of classical conditioning. Let’s say you have a cat named Tiger, who is quite spoiled. You keep her food in a separate cabinet, and you also have a special electric can opener that you use only to open cans of cat food. For every meal, Tiger hears the distinctive sound of the electric can opener (“zzhzhz”) and then gets her food. Tiger quickly learns that when she hears “zzhzhz” she is about to get fed. What do you think Tiger does when she hears the electric can opener? She will likely get excited and run to where you are preparing her food. This is an example of classical conditioning. In this case, what are the UCS, CS, UCR, and CR?

What if the cabinet holding Tiger’s food becomes squeaky? In that case, Tiger hears “squeak” (the cabinet), “zzhzhz” (the electric can opener), and then she gets her food. Tiger will learn to get excited when she hears the “squeak” of the cabinet. Pairing a new neutral stimulus (“squeak”) with the conditioned stimulus (“zzhzhz”) is called higher-order conditioning , or second-order conditioning . This means you are using the conditioned stimulus of the can opener to condition another stimulus: the squeaky cabinet ( Figure 6.5 ). It is hard to achieve anything above second-order conditioning. For example, if you ring a bell, open the cabinet (“squeak”), use the can opener (“zzhzhz”), and then feed Tiger, Tiger will likely never get excited when hearing the bell alone.

Everyday Connection

Classical conditioning at stingray city.

Kate and her spouse recently vacationed in the Cayman Islands, and booked a boat tour to Stingray City, where they could feed and swim with the southern stingrays. The boat captain explained how the normally solitary stingrays have become accustomed to interacting with humans. About 40 years ago, people began to clean fish and conch (unconditioned stimulus) at a particular sandbar near a barrier reef, and large numbers of stingrays would swim in to eat (unconditioned response) what the people threw into the water; this continued for years. By the late 1980s, word of the large group of stingrays spread among scuba divers, who then started feeding them by hand. Over time, the southern stingrays in the area were classically conditioned much like Pavlov’s dogs. When they hear the sound of a boat engine (neutral stimulus that becomes a conditioned stimulus), they know that they will get to eat (conditioned response).

As soon as they reached Stingray City, over two dozen stingrays surrounded their tour boat. The couple slipped into the water with bags of squid, the stingrays’ favorite treat. The swarm of stingrays bumped and rubbed up against their legs like hungry cats ( Figure 6.6 ). Kate was able to feed, pet, and even kiss (for luck) these amazing creatures. Then all the squid was gone, and so were the stingrays.

Classical conditioning also applies to humans, even babies. For example, Elan buys formula in blue canisters for their six-month-old daughter, Angelina. Whenever Elan takes out a formula container, Angelina gets excited, tries to reach toward the food, and most likely salivates. Why does Angelina get excited when she sees the formula canister? What are the UCS, CS, UCR, and CR here?

So far, all of the examples have involved food, but classical conditioning extends beyond the basic need to be fed. Consider our earlier example of a dog whose owners install an invisible electric dog fence. A small electrical shock (unconditioned stimulus) elicits discomfort (unconditioned response). When the unconditioned stimulus (shock) is paired with a neutral stimulus (the edge of a yard), the dog associates the discomfort (unconditioned response) with the edge of the yard (conditioned stimulus) and stays within the set boundaries. In this example, the edge of the yard elicits fear and anxiety in the dog. Fear and anxiety are the conditioned response.

Watch this video clip from the television show, The Office , for a humorous look at conditioning in which Jim conditions Dwight to expect a breath mint every time Jim’s computer makes a specific sound.

General Processes in Classical Conditioning

Now that you know how classical conditioning works and have seen several examples, let’s take a look at some of the general processes involved. In classical conditioning, the initial period of learning is known as acquisition , when an organism learns to connect a neutral stimulus and an unconditioned stimulus. During acquisition, the neutral stimulus begins to elicit the conditioned response, and eventually the neutral stimulus becomes a conditioned stimulus capable of eliciting the conditioned response by itself. Timing is important for conditioning to occur. Typically, there should only be a brief interval between presentation of the conditioned stimulus and the unconditioned stimulus. Depending on what is being conditioned, sometimes this interval is as little as five seconds (Chance, 2009). However, with other types of conditioning, the interval can be up to several hours.

Taste aversion is a type of conditioning in which an interval of several hours may pass between the conditioned stimulus (something ingested) and the unconditioned stimulus (nausea or illness). Here’s an example. Harry went to the carnival. He ate a lot of cotton candy and later that night was very sick and threw up. The next day, his friend offered him a piece of candy. He put it into his mouth and started to feel sick and had to spit it out. The unconditioned stimulus is eating too much cotton candy. The unconditioned response is getting sick and throwing up. The conditioned stimulus is the sugary flavor and the conditioned response is Harry feeling nauseous at the taste of sugar.

How does this occur—conditioning based on a single instance and involving an extended time lapse between the event and the negative stimulus? Research into taste aversion suggests that this response may be an evolutionary adaptation designed to help organisms quickly learn to avoid harmful foods (Garcia & Rusiniak, 1980; Garcia & Koelling, 1966). Not only may this contribute to species survival via natural selection, but it may also help us develop strategies for challenges such as helping cancer patients through the nausea induced by certain treatments (Holmes, 1993; Jacobsen et al., 1993; Hutton, Baracos, & Wismer, 2007; Skolin et al., 2006). Garcia and Koelling (1966) showed not only that taste aversions could be conditioned, but also that there were biological constraints to learning. In their study, separate groups of rats were conditioned to associate either a flavor with illness, or lights and sounds with illness. Results showed that all rats exposed to flavor-illness pairings learned to avoid the flavor, but none of the rats exposed to lights and sounds with illness learned to avoid lights or sounds. This added evidence to the idea that classical conditioning could contribute to species survival by helping organisms learn to avoid stimuli that posed real dangers to health and welfare.

Robert Rescorla demonstrated how powerfully an organism can learn to predict the UCS from the CS. Take, for example, the following two situations. Ari’s dad always has dinner on the table every day at 6:00. Soraya’s mom switches it up so that some days they eat dinner at 6:00, some days they eat at 5:00, and other days they eat at 7:00. For Ari, 6:00 reliably and consistently predicts dinner, so Ari will likely start feeling hungry every day right before 6:00, even if he's had a late snack. Soraya, on the other hand, will be less likely to associate 6:00 with dinner, since 6:00 does not always predict that dinner is coming. Rescorla, along with his colleague at Yale University, Allan Wagner, developed a mathematical formula that could be used to calculate the probability that an association would be learned given the ability of a conditioned stimulus to predict the occurrence of an unconditioned stimulus and other factors; today this is known as the Rescorla-Wagner model (Rescorla & Wagner, 1972)

Once we have established the connection between the unconditioned stimulus and the conditioned stimulus, how do we break that connection and get the dog, cat, or child to stop responding? In Tiger’s case, imagine what would happen if you stopped using the electric can opener for her food and began to use it only for human food. Now, Tiger would hear the can opener, but she would not get food. In classical conditioning terms, you would be giving the conditioned stimulus, but not the unconditioned stimulus. Pavlov explored this scenario in his experiments with dogs: sounding the tone without giving the dogs the meat powder. Soon the dogs stopped responding to the tone. Extinction is the decrease in the conditioned response when the unconditioned stimulus is no longer presented with the conditioned stimulus. When presented with the conditioned stimulus alone, the dog, cat, or other organism would show a weaker and weaker response, and finally no response. In classical conditioning terms, there is a gradual weakening and disappearance of the conditioned response.

What happens when learning is not used for a while—when what was learned lies dormant? As we just discussed, Pavlov found that when he repeatedly presented the bell (conditioned stimulus) without the meat powder (unconditioned stimulus), extinction occurred; the dogs stopped salivating to the bell. However, after a couple of hours of resting from this extinction training, the dogs again began to salivate when Pavlov rang the bell. What do you think would happen with Tiger’s behavior if your electric can opener broke, and you did not use it for several months? When you finally got it fixed and started using it to open Tiger’s food again, Tiger would remember the association between the can opener and her food—she would get excited and run to the kitchen when she heard the sound. The behavior of Pavlov’s dogs and Tiger illustrates a concept Pavlov called spontaneous recovery : the return of a previously extinguished conditioned response following a rest period ( Figure 6.7 ).

Of course, these processes also apply in humans. For example, let’s say that every day when you walk to campus, an ice cream truck passes your route. Day after day, you hear the truck’s music (neutral stimulus), so you finally stop and purchase a chocolate ice cream bar. You take a bite (unconditioned stimulus) and then your mouth waters (unconditioned response). This initial period of learning is known as acquisition, when you begin to connect the neutral stimulus (the sound of the truck) and the unconditioned stimulus (the taste of the chocolate ice cream in your mouth). During acquisition, the conditioned response gets stronger and stronger through repeated pairings of the conditioned stimulus and unconditioned stimulus. Several days (and ice cream bars) later, you notice that your mouth begins to water (conditioned response) as soon as you hear the truck’s musical jingle—even before you bite into the ice cream bar. Then one day you head down the street. You hear the truck’s music (conditioned stimulus), and your mouth waters (conditioned response). However, when you get to the truck, you discover that they are all out of ice cream. You leave disappointed. The next few days you pass by the truck and hear the music, but don’t stop to get an ice cream bar because you’re running late for class. You begin to salivate less and less when you hear the music, until by the end of the week, your mouth no longer waters when you hear the tune. This illustrates extinction. The conditioned response weakens when only the conditioned stimulus (the sound of the truck) is presented, without being followed by the unconditioned stimulus (chocolate ice cream in the mouth). Then the weekend comes. You don’t have to go to class, so you don’t pass the truck. Monday morning arrives and you take your usual route to campus. You round the corner and hear the truck again. What do you think happens? Your mouth begins to water again. Why? After a break from conditioning, the conditioned response reappears, which indicates spontaneous recovery.

Acquisition and extinction involve the strengthening and weakening, respectively, of a learned association. Two other learning processes—stimulus discrimination and stimulus generalization—are involved in determining which stimuli will trigger learned responses. Animals (including humans) need to distinguish between stimuli—for example, between sounds that predict a threatening event and sounds that do not—so that they can respond appropriately (such as running away if the sound is threatening). When an organism learns to respond differently to various stimuli that are similar, it is called stimulus discrimination . In classical conditioning terms, the organism demonstrates the conditioned response only to the conditioned stimulus. Pavlov’s dogs discriminated between the basic tone that sounded before they were fed and other tones (e.g., the doorbell), because the other sounds did not predict the arrival of food. Similarly, Tiger, the cat, discriminated between the sound of the can opener and the sound of the electric mixer. When the electric mixer is going, Tiger is not about to be fed, so she does not come running to the kitchen looking for food. In our other example, Moisha, the cancer patient, discriminated between oncologists and other types of doctors. She learned not to feel ill when visiting doctors for other types of appointments, such as her annual physical.

On the other hand, when an organism demonstrates the conditioned response to stimuli that are similar to the condition stimulus, it is called stimulus generalization , the opposite of stimulus discrimination. The more similar a stimulus is to the condition stimulus, the more likely the organism is to give the conditioned response. For instance, if the electric mixer sounds very similar to the electric can opener, Tiger may come running after hearing its sound. But if you do not feed her following the electric mixer sound, and you continue to feed her consistently after the electric can opener sound, she will quickly learn to discriminate between the two sounds (provided they are sufficiently dissimilar that she can tell them apart). In our other example, Moisha continued to feel ill whenever visiting other oncologists or other doctors in the same building as her oncologist.

Behaviorism

John B. Watson , shown in Figure 6.8 , is considered the founder of behaviorism. Behaviorism is a school of thought that arose during the first part of the 20th century, which incorporates elements of Pavlov’s classical conditioning (Hunt, 2007). In stark contrast with Freud, who considered the reasons for behavior to be hidden in the unconscious, Watson championed the idea that all behavior can be studied as a simple stimulus-response reaction, without regard for internal processes. Watson argued that in order for psychology to become a legitimate science, it must shift its concern away from internal mental processes because mental processes cannot be seen or measured. Instead, he asserted that psychology must focus on outward observable behavior that can be measured.

Watson’s ideas were influenced by Pavlov’s work. According to Watson, human behavior, just like animal behavior, is primarily the result of conditioned responses. Whereas Pavlov’s work with dogs involved the conditioning of reflexes, Watson believed the same principles could be extended to the conditioning of human emotions (Watson, 1919).

In 1920, while chair of the psychology department at Johns Hopkins University, Watson and his graduate student, Rosalie Rayner, conducted research on a baby nicknamed Little Albert. Rayner and Watson’s experiments with Little Albert demonstrated how fears can be conditioned using classical conditioning. Through these experiments, Little Albert was exposed to and conditioned to fear certain things. Initially he was presented with various neutral stimuli, including a rabbit, a dog, a monkey, masks, cotton wool, and a white rat. He was not afraid of any of these things. Then Watson, with the help of Rayner, conditioned Little Albert to associate these stimuli with an emotion—fear. For example, Watson handed Little Albert the white rat, and Little Albert enjoyed playing with it. Then Watson made a loud sound, by striking a hammer against a metal bar hanging behind Little Albert’s head, each time Little Albert touched the rat. Little Albert was frightened by the sound—demonstrating a reflexive fear of sudden loud noises—and began to cry. Watson repeatedly paired the loud sound with the white rat. Soon Little Albert became frightened by the white rat alone. In this case, what are the UCS, CS, UCR, and CR? Days later, Little Albert demonstrated stimulus generalization—he became afraid of other furry things: a rabbit, a furry coat, and even a Santa Claus mask ( Figure 6.9 ). Watson had succeeded in conditioning a fear response in Little Albert, thus demonstrating that emotions could become conditioned responses. It had been Watson’s intention to produce a phobia—a persistent, excessive fear of a specific object or situation— through conditioning alone, thus countering Freud’s view that phobias are caused by deep, hidden conflicts in the mind. However, there is no evidence that Little Albert experienced phobias in later years. While Watson’s research provided new insight into conditioning, it would be considered unethical by today’s standards.

View scenes from this video on John Watson’s experiment in which Little Albert was conditioned to respond in fear to furry objects to learn more.

As you watch the video, look closely at Little Albert’s reactions and the manner in which Watson and Rayner present the stimuli before and after conditioning. Based on what you see, would you come to the same conclusions as the researchers?

Advertising and Associative Learning

Advertising executives are pros at applying the principles of associative learning. Think about the car commercials you have seen on television. Many of them feature an attractive model. By associating the model with the car being advertised, you come to see the car as being desirable (Cialdini, 2008). You may be asking yourself, does this advertising technique actually work? According to Cialdini (2008), men who viewed a car commercial that included an attractive model later rated the car as being faster, more appealing, and better designed than did men who viewed an advertisement for the same car minus the model.

Have you ever noticed how quickly advertisers cancel contracts with a famous athlete following a scandal? As far as the advertiser is concerned, that athlete is no longer associated with positive feelings; therefore, the athlete cannot be used as an unconditioned stimulus to condition the public to associate positive feelings (the unconditioned response) with their product (the conditioned stimulus).

Now that you are aware of how associative learning works, see if you can find examples of these types of advertisements on television, in magazines, or on the Internet.

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Access for free at https://openstax.org/books/psychology-2e/pages/1-introduction

• Authors: Rose M. Spielman, William J. Jenkins, Marilyn D. Lovett
• Publisher/website: OpenStax
• Book title: Psychology 2e
• Publication date: Apr 22, 2020
• Location: Houston, Texas
• Book URL: https://openstax.org/books/psychology-2e/pages/1-introduction
• Section URL: https://openstax.org/books/psychology-2e/pages/6-2-classical-conditioning

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Pavlov's Dogs and the Discovery of Classical Conditioning

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• Pavlov's Theory

Pavlov's dog experiments played a critical role in the discovery of one of the most important concepts in psychology: Classical conditioning .

While it happened quite by accident, Pavlov's famous experiments had a major impact on our understanding of how learning takes place as well as the development of the school of behavioral psychology. Classical conditioning is sometimes called Pavlovian conditioning.

Pavlov's Dog: A Background

How did experiments on the digestive response in dogs lead to one of the most important discoveries in psychology? Ivan Pavlov was a noted Russian physiologist who won the 1904 Nobel Prize for his work studying digestive processes.

While studying digestion in dogs, Pavlov noted an interesting occurrence: His canine subjects would begin to salivate whenever an assistant entered the room.

The concept of classical conditioning is studied by every entry-level psychology student, so it may be surprising to learn that the man who first noted this phenomenon was not a psychologist at all.

In his digestive research, Pavlov and his assistants would introduce a variety of edible and non-edible items and measure the saliva production that the items produced.

Salivation, he noted, is a reflexive process. It occurs automatically in response to a specific stimulus and is not under conscious control.

However, Pavlov noted that the dogs would often begin salivating in the absence of food and smell. He quickly realized that this salivary response was not due to an automatic, physiological process.

Pavlov's Theory of Classical Conditioning

Based on his observations, Pavlov suggested that the salivation was a learned response. Pavlov's dog subjects were responding to the sight of the research assistants' white lab coats, which the animals had come to associate with the presentation of food.

Unlike the salivary response to the presentation of food, which is an unconditioned reflex, salivating to the expectation of food is a conditioned reflex.

Pavlov then focused on investigating exactly how these conditioned responses are learned or acquired. In a series of experiments, he set out to provoke a conditioned response to a previously neutral stimulus.

He opted to use food as the unconditioned stimulus , or the stimulus that evokes a response naturally and automatically. The sound of a metronome was chosen to be the neutral stimulus.

The dogs would first be exposed to the sound of the ticking metronome, and then the food was immediately presented.

After several conditioning trials, Pavlov noted that the dogs began to salivate after hearing the metronome. "A stimulus which was neutral in and of itself had been superimposed upon the action of the inborn alimentary reflex," Pavlov wrote of the results.

"We observed that, after several repetitions of the combined stimulation, the sounds of the metronome had acquired the property of stimulating salivary secretion."

In other words, the previously neutral stimulus (the metronome) had become what is known as a conditioned stimulus that then provoked a conditioned response (salivation).

To review, the following are some key components used in Pavlov's theory:

• Conditioned stimulus : This is what the neutral stimulus becomes after training (i.e., the metronome was the conditioned stimulus after Pavlov trained the dogs to respond to it)
• Unconditioned stimulus : A stimulus that produces an automatic response (i.e., the food was the unconditioned stimulus because it made the dogs automatically salivate)
• Conditioned response (conditioned reflex) : A learned response to previously neutral stimulus (i.e., the salivation was a conditioned response to the metronome)
• Unconditioned response (unconditioned reflex) : A response that is automatic (i.e., the dog's salivating is an unconditioned response to the food)

Impact of Pavlov's Research

Pavlov's discovery of classical conditioning remains one of the most important in psychology's history.

In addition to forming the basis of what would become behavioral psychology , the classical conditioning process remains important today for numerous applications, including behavioral modification and mental health treatment.

Principles of classical conditioning are used to treat the following mental health disorders:

• Obsessive-compulsive disorder (OCD)
• Panic attacks and panic disorder
• Substance use disorders

For instance, a specific type of treatment called aversion therapy uses conditioned responses to help people with anxiety or a specific phobia.

A therapist will help a person face the object of their fear gradually—while helping them manage any fear responses that arise. Gradually, the person will form a neutral response to the object.

Pavlov’s work has also inspired research on how to apply classical conditioning principles to taste aversions . The principles have been used to prevent coyotes from preying on domestic livestock and to use neutral stimulus (eating some type of food) paired with an unconditioned response (negative results after eating the food) to create an aversion to a particular food.

Unlike other forms of classical conditioning, this type of conditioning does not require multiple pairings in order for an association to form. In fact, taste aversions generally occur after just a single pairing. Ranchers have found ways to put this form of classical conditioning to good use to protect their herds.

In one example, mutton was injected with a drug that produces severe nausea. After eating the poisoned meat, coyotes then avoided sheep herds rather than attack them.

A Word From Verywell

While Pavlov's discovery of classical conditioning formed an essential part of psychology's history, his work continues to inspire further research today. His contributions to psychology have helped make the discipline what it is today and will likely continue to shape our understanding of human behavior for years to come.

Adams M. The kingdom of dogs: Understanding Pavlov’s experiments as human–animal relationships . Theory & Psychology . 2019;30(1):121-141. doi:10.1177/0959354319895597

Fanselow MS, Wassum KM.  The origins and organization of vertebrate Pavlovian conditioning .  Cold Spring Harb Perspect Biol.  2015;8(1):a021717. doi:10.1101/cshperspect.a021717

Nees F, Heinrich A, Flor H.  A mechanism-oriented approach to psychopathology: The role of Pavlovian conditioning .  Int J Psychophysiol.  2015;98(2):351-364. doi:10.1016/j.ijpsycho.2015.05.005

American Psychological Association. What is exposure therapy?

Lin JY, Arthurs J, Reilly S. Conditioned taste aversions: From poisons to pain to drugs of abuse. Psychon Bull Rev . 2017;24(2):335-351. doi:10.3758/s13423-016-1092-8

Gustafson, C.R., Kelly, D.J, Sweeney, M., & Garcia, J. Prey-lithium aversions: I. Coyotes and wolves. Behavioral Biology. 1976; 17:  61-72.

Hock, R.R. Forty studies that changed psychology: Explorations into the history of psychological research. (4th ed.).  New Jersey: Pearson Education; 2002.

• Gustafson, C.R., Garcia, J., Hawkins, W., & Rusiniak, K. Coyote predation control by aversive conditioning.   Science. 1974; 184:  581-583.
• Pavlov, I.P. Conditioned reflexes .  London: Oxford University Press; 1927.

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Classical Conditioning: How It Works With Examples

Saul McLeod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

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Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

On This Page:

Classical conditioning (also known as Pavlovian or respondent conditioning) is learning through association and was discovered by Pavlov , a Russian physiologist. In simple terms, two stimuli are linked together to produce a new learned response in a person or animal.

John Watson proposed that the process of classical conditioning (based on Pavlov’s observations) was able to explain all aspects of human psychology.

If you pair a neutral stimulus (NS) with an unconditioned stimulus (US) that already triggers an unconditioned response (UR) that neutral stimulus will become a conditioned stimulus (CS), triggering a conditioned response (CR) similar to the original unconditioned response.

Everything from speech to emotional responses was simply patterns of stimulus and response. Watson completely denied the existence of the mind or consciousness. Watson believed that all individual differences in behavior were due to different learning experiences.

Watson (1924, p. 104) famously said:

Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I’ll guarantee to take any one at random and train him to become any type of specialist I might select – doctor, lawyer, artist, merchant-chief and, yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations and the race of his ancestors.

How Classical Conditioning Works

There are three stages of classical conditioning. At each stage, the stimuli and responses are given special scientific terms:

Stage 1: Before Conditioning:

In this stage, the unconditioned stimulus (UCS) produces an unconditioned response (UCR) in an organism.

In basic terms, this means that a stimulus in the environment has produced a behavior/response that is unlearned (i.e., unconditioned) and, therefore, is a natural response that has not been taught. In this respect, no new behavior has been learned yet.

For example, a stomach virus (UCS) would produce a response of nausea (UCR). In another example, a perfume (UCS) could create a response of happiness or desire (UCR).

This stage also involves another stimulus that has no effect on a person and is called the neutral stimulus (NS). The NS could be a person, object, place, etc.

The neutral stimulus in classical conditioning does not produce a response until it is paired with the unconditioned stimulus.

Stage 2: During Conditioning:

During this stage, a stimulus which produces no response (i.e., neutral) is associated with the unconditioned stimulus, at which point it now becomes known as the conditioned stimulus (CS).

For example, a stomach virus (UCS) might be associated with eating a certain food such as chocolate (CS). Also, perfume (UCS) might be associated with a specific person (CS).

For classical conditioning to be effective, the conditioned stimulus should occur before the unconditioned stimulus, rather than after it, or during the same time. Thus, the conditioned stimulus acts as a type of signal or cue for the unconditioned stimulus.

In some cases, conditioning may take place if the NS occurs after the UCS (backward conditioning), but this normally disappears quite quickly. The most important aspect of the conditioning stimulus is the it helps the organism predict the coming of the unconditional stimulus.

Often during this stage, the UCS must be associated with the CS on a number of occasions, or trials, for learning to take place.

However, one trial learning can happen on certain occasions when it is not necessary for an association to be strengthened over time (such as being sick after food poisoning or drinking too much alcohol).

Stage 3: After Conditioning:

The conditioned stimulus (CS) has been associated with the unconditioned stimulus (UCS) to create a new conditioned response (CR).

For example, a person (CS) who has been associated with nice perfume (UCS) is now found attractive (CR). Also, chocolate (CS) which was eaten before a person was sick with a virus (UCS) now produces a response of nausea (CR).

Classical Conditioning Examples

Pavlov’s dogs.

The most famous example of classical conditioning was Ivan Pavlov’s experiment with dogs , who salivated in response to a bell tone. Pavlov showed that when a bell was sounded each time the dog was fed, the dog learned to associate the sound with the presentation of the food.

He first presented the dogs with the sound of a bell; they did not salivate so this was a neutral stimulus. Then he presented them with food, they salivated. The food was an unconditioned stimulus, and salivation was an unconditioned (innate) response.

He then repeatedly presented the dogs with the sound of the bell first and then the food (pairing) after a few repetitions, the dogs salivated when they heard the sound of the bell. The bell had become the conditioned stimulus and salivation had become the conditioned response.

Fear Response

Watson & Rayner (1920) were the first psychologists to apply the principles of classical conditioning to human behavior by looking at how this learning process may explain the development of phobias.

They did this in what is now considered to be one of the most ethically dubious experiments ever conducted – the case of Little Albert . Albert B.’s mother was a wet nurse in a children’s hospital. Albert was described as ‘healthy from birth’ and ‘on the whole stolid and unemotional’.

When he was about nine months old, his reactions to various stimuli (including a white rat, burning newspapers, and a hammer striking a four-foot steel bar just behind his head) were tested.

Only the last of these frightened him, so this was designated the unconditioned stimulus (UCS) and fear the unconditioned response (UCR). The other stimuli were neutral because they did not produce fear.

When Albert was just over eleven months old, the rat and the UCS were presented together: as Albert reached out to stroke the animal, Watson struck the bar behind his head.

This occurred seven times in total over the next seven weeks. By this time, the rat, the conditioned stimulus (CS), on its own frightened Albert, and fear was now a conditioned response (CR).

The CR transferred spontaneously to the rabbit, the dog, and other stimuli that had been previously neutral. Five days after conditioning, the CR produced by the rat persisted. After ten days, it was ‘much less marked’, but it was still evident a month later.

Carter and Tiffany (1999) support the cue reactivity theory, they carried out a meta-analysis reviewing 41 cue-reactivity studies that compared responses of alcoholics, cigarette smokers, cocaine addicts and heroin addicts to drug-related versus neutral stimuli.

They found that dependent individuals reacted strongly to the cues presented and reported craving and physiological arousal.

Panic Disorder

Classical conditioning is thought to play an important role in the development of Pavlov (Bouton et al., 2002).

Panic disorder often begins after an initial “conditioning episode” involving an early panic attack. The panic attack serves as an unconditioned stimulus (US) that gets paired with neutral stimuli (conditioned stimuli or CS), allowing those stimuli to later trigger anxiety and panic reactions (conditioned responses or CRs).

The panic attack US can become associated with interoceptive cues (like increased heart rate) as well as external situational cues that are present during the attack. This allows those cues to later elicit anxiety and possibly panic (CRs).

Through this conditioning process, anxiety becomes focused on the possibility of having another panic attack. This anticipatory anxiety (a CR) is seen as a key step in the development of panic disorder, as it leads to heightened vigilance and sensitivity to bodily cues that can trigger future attacks.

The presence of conditioned anxiety can serve to potentiate or exacerbate future panic attacks. Anxiety cues essentially lower the threshold for panic. This helps explain how panic disorder can spiral after the initial conditioning episode.

Evidence suggests most patients with panic disorder recall an initial panic attack or conditioning event that preceded the disorder. Prospective studies also show conditioned anxiety and panic reactions can develop after an initial panic episode.

Classical conditioning processes are believed to often occur outside of conscious awareness in panic disorder, reflecting the operation of emotional neural systems separate from declarative knowledge systems.

Cue reactivity is the theory that people associate situations (e.g., meeting with friends)/ places (e.g., pub) with the rewarding effects of nicotine, and these cues can trigger a feeling of craving (Carter & Tiffany, 1999).

These factors become smoking-related cues. Prolonged use of nicotine creates an association between these factors and smoking based on classical conditioning.

Nicotine is the unconditioned stimulus (UCS), and the pleasure caused by the sudden increase in dopamine levels is the unconditioned response (UCR). Following this increase, the brain tries to lower the dopamine back to a normal level.

The stimuli that have become associated with nicotine were neutral stimuli (NS) before “learning” took place but they became conditioned stimuli (CS), with repeated pairings. They can produce the conditioned response (CR).

However, if the brain has not received nicotine, the levels of dopamine drop, and the individual experiences withdrawal symptoms therefore is more likely to feel the need to smoke in the presence of the cues that have become associated with the use of nicotine.

Classroom Learning

The implications of classical conditioning in the classroom are less important than those of operant conditioning , but there is still a need for teachers to try to make sure that students associate positive emotional experiences with learning.

If a student associates negative emotional experiences with school, then this can obviously have bad results, such as creating a school phobia.

For example, if a student is bullied at school they may learn to associate the school with fear. It could also explain why some students show a particular dislike of certain subjects that continue throughout their academic career. This could happen if a student is humiliated or punished in class by a teacher.

Principles of Classical Conditioning

Neutral stimulus.

In classical conditioning, a neutral stimulus (NS) is a stimulus that initially does not evoke a response until it is paired with the unconditioned stimulus.

For example, in Pavlov’s experiment, the bell was the neutral stimulus, and only produced a response when paired with food.

Unconditioned Stimulus

Unconditioned response.

In classical conditioning, an unconditioned response is an innate response that occurs automatically when the unconditioned stimulus is presented.

Pavlov showed the existence of the unconditioned response by presenting a dog with a bowl of food and measuring its salivary secretions.

Conditioned Stimulus

Conditioned response.

In classical conditioning, the conditioned response (CR) is the learned response to the previously neutral stimulus.

In Ivan Pavlov’s experiments in classical conditioning, the dog’s salivation was the conditioned response to the sound of a bell.

Acquisition

The process of pairing a neutral stimulus with an unconditioned stimulus to produce a conditioned response.

In the initial learning period, acquisition describes when an organism learns to connect a neutral stimulus and an unconditioned stimulus.

In psychology, extinction refers to the gradual weakening of a conditioned response by breaking the association between the conditioned and the unconditioned stimuli.

The weakening of a conditioned response occurs when the conditioned stimulus is repeatedly presented without the unconditioned stimulus.

For example, when the bell repeatedly rang, and no food was presented, Pavlov’s dog gradually stopped salivating at the sound of the bell.

Spontaneous Recovery

Spontaneous recovery is a phenomenon of Pavlovian conditioning that refers to the return of a conditioned response (in a weaker form) after a period of time following extinction.

It is the reappearance of an extinguished conditioned response after a rest period when the conditioned stimulus is presented alone.

For example, when Pavlov waited a few days after extinguishing the conditioned response, and then rang the bell once more, the dog salivated again.

Generalization

In psychology, generalization is the tendency to respond in the same way to stimuli similar (but not identical) to the original conditioned stimulus.

For example, in Pavlov’s experiment, if a dog is conditioned to salivate to the sound of a bell, it may later salivate to a higher-pitched bell.

Discrimination

In classical conditioning, discrimination is a process through which individuals learn to differentiate among similar stimuli and respond appropriately to each one.

For example, eventually, Pavlov’s dog learns the difference between the sound of the 2 bells and no longer salivates at the sound of the non-food bell.

Higher-Order Conditioning

Higher-order conditioning is when a conditioned stimulus is paired with a new neutral stimulus to create a second conditioned stimulus. For example, a bell (CS1) is paired with food (UCS) so that the bell elicits salivation (CR). Then, a light (NS) is paired with the bell.

Eventually, the light alone will elicit salivation, even without the presence of food. This demonstrates higher-order conditioning, where the conditioned stimulus (bell) serves as an unconditioned stimulus to condition a new stimulus (light).

Critical Evaluation

Practical applications.

The principles of classical conditioning have been widely and effectively applied in fields like behavioral therapy, education, and advertising. Therapies like systematic desensitization use classical conditioning to help eliminate phobias and anxiety.

The behaviorist approach has been used in the treatment of phobias, and systematic desensitization . The individual with the phobia is taught relaxation techniques and then makes a hierarchy of fear from the least frightening to the most frightening features of the phobic object.

He then is presented with the stimuli in that order and learns to associate (classical conditioning) the stimuli with a relaxation response. This is counter-conditioning.

Explaining involuntary behaviors

Classical conditioning helps explain some reflexive or involuntary behaviors like phobias, emotional reactions, and physiological responses. The model shows how these can be acquired through experience.

The process of classical conditioning can probably account for aspects of certain other mental disorders. For example, in post-traumatic stress disorder (PTSD), sufferers tend to show classically conditioned responses to stimuli present at the time of the traumatizing event (Charney et al., 1993).

However, since not everyone exposed to the traumatic event develops PTSD, other factors must be involved, such as individual differences in people’s appraisal of events as stressors and the recovery environment, such as family and support groups.

Supported by substantial experimental evidence

There is a wealth of experimental support for basic phenomena like acquisition, extinction, generalization, and discrimination. Pavlov’s original experiments on dogs and subsequent studies have demonstrated classical conditioning in animals and humans.

There have been many laboratory demonstrations of human participants acquiring behavior through classical conditioning. It is relatively easy to classically condition and extinguish conditioned responses, such as the eye-blink and galvanic skin responses.

A strength of classical conditioning theory is that it is scientific . This is because it’s based on empirical evidence carried out by controlled experiments . For example, Pavlov (1902) showed how classical conditioning could be used to make a dog salivate to the sound of a bell.

Supporters of a reductionist approach say that it is scientific. Breaking complicated behaviors down into small parts means that they can be scientifically tested. However, some would argue that the reductionist view lacks validity . Thus, while reductionism is useful, it can lead to incomplete explanations.

Ignores biological predispositions

Organisms are biologically prepared to associate certain stimuli over others. However, classical conditioning does not sufficiently account for innate predispositions and biases.

Classical conditioning emphasizes the importance of learning from the environment, and supports nurture over nature.

However, it is limiting to describe behavior solely in terms of either nature or nurture , and attempts to do this underestimate the complexity of human behavior. It is more likely that behavior is due to an interaction between nature (biology) and nurture (environment).

Lacks explanatory power

Classical conditioning provides limited insight into the cognitive processes underlying the associations it describes.

However, applying classical conditioning to our understanding of higher mental functions, such as memory, thinking, reasoning, or problem-solving, has proved more problematic.

Even behavior therapy, one of the more successful applications of conditioning principles to human behavior, has given way to cognitive–behavior therapy (Mackintosh, 1995).

Questionable ecological validity

While lab studies support classical conditioning, some question how well it holds up in natural settings. There is debate about how automatic and inevitable classical conditioning is outside the lab.

In normal adults, the conditioning process can be overridden by instructions: simply telling participants that the unconditioned stimulus will not occur causes an instant loss of the conditioned response, which would otherwise extinguish only slowly (Davey, 1983).

Most participants in an experiment are aware of the experimenter’s contingencies (the relationship between stimuli and responses) and, in the absence of such awareness often fail to show evidence of conditioning (Brewer, 1974).

Evidence indicates that for humans to exhibit classical conditioning, they need to be consciously aware of the connection between the conditioned stimulus (CS) and the unconditioned stimulus (US). This contradicts traditional theories that humans have two separate learning systems – one conscious and one unconscious – that allow conditioning to occur without conscious awareness (Lovibond & Shanks, 2002).

There are also important differences between very young children or those with severe learning difficulties and older children and adults regarding their behavior in a variety of operant conditioning and discrimination learning experiments.

These seem largely attributable to language development (Dugdale & Lowe, 1990). This suggests that people have rather more efficient, language-based forms of learning at their disposal than just the laborious formation of associations between a conditioned stimulus and an unconditioned stimulus.

Ethical concerns

The principles of classical conditioning raise ethical concerns about manipulating behavior without consent. This is especially true in advertising and politics.

• Manipulation of preferences – Classical conditioning can create positive associations with certain brands, products, or political candidates. This can manipulate preferences outside of a person’s rational thought process.
• Encouraging impulsive behaviors – Conditioning techniques may encourage behaviors like impulsive shopping, unhealthy eating, or risky financial choices by forging positive associations with these behaviors.
• Preying on vulnerabilities – Advertisers or political campaigns may exploit conditioning techniques to target and influence vulnerable demographic groups like youth, seniors, or those with mental health conditions.
• Reduction of human agency – At an extreme, the use of classical conditioning techniques reduces human beings to automata reacting predictably to stimuli. This is ethically problematic.

Deterministic theory

A final criticism of classical conditioning theory is that it is deterministic . This means it does not allow the individual any degree of free will. Accordingly, a person has no control over the reactions they have learned from classical conditioning, such as a phobia.

The deterministic approach also has important implications for psychology as a science. Scientists are interested in discovering laws that can be used to predict events.

However, by creating general laws of behavior, deterministic psychology underestimates the uniqueness of human beings and their freedom to choose their destiny.

The Role of Nature in Classical Conditioning

Behaviorists argue all learning is driven by experience, not nature. Classical conditioning exemplifies environmental influence. However, our evolutionary history predisposes us to learn some associations more readily than others. So nature also plays a role.

For example, PTSD develops in part due to strong conditioning during traumatic events. The emotions experienced during trauma lead to neural activity in the amygdala , creating strong associative learning between conditioned and unconditioned stimuli (Milad et al., 2009).

Individuals with PTSD show enhanced fear conditioning, reflected in greater amygdala reactivity to conditioned threat cues compared to trauma-exposed controls. In addition to strong initial conditioning, PTSD patients exhibit slower extinction to conditioned fear stimuli.

During extinction recall tests, PTSD patients fail to show differential skin conductance responses to extinguished versus non-extinguished cues, indicating impaired retention of fear extinction. Deficient extinction retention corresponds to reduced activation in the ventromedial prefrontal cortex and hippocampus and heightened dorsal anterior cingulate cortex response during extinction recall in PTSD patients.

In influential research on food conditioning, John Garcia found that rats easily learned to associate a taste with nausea from drugs, even if illness occurred hours later.

However, conditioning nausea to a sight or sound was much harder. This showed that conditioning does not occur equally for any stimulus pairing. Rather, evolution prepares organisms to learn some associations that aid survival more easily, like linking smells to illness.

The evolutionary significance of taste and nutrition ensures robust and resilient classical conditioning of flavor preferences, making them difficult to reverse (Hall, 2002).

Forming strong and lasting associations between flavors and nutrition aids survival by promoting the consumption of calorie-rich foods. This makes flavor conditioning very robust.

Repeated flavor-nutrition pairings in these studies lead to overlearning of the association, making it more resistant to extinction.

The learning is overtrained, context-specific, and subject to recovery effects that maintain the conditioned behavior despite extinction training.

Classical vs. operant condioning

In summary, classical conditioning is about passive stimulus-response associations, while operant conditioning is about actively connecting behaviors to consequences. Classical works on reflexes and operant on voluntary actions.

• Stimuli vs consequences : Classical conditioning focuses on associating two stimuli together. For example, pairing a bell (neutral stimulus) with food (reflex-eliciting stimulus) creates a conditioned response of salivation to the bell. Operant conditioning is about connecting behaviors with the consequences that follow. If a behavior is reinforced, it will increase. If it’s punished, it will decrease.
• Passive vs. active : In classical conditioning, the organism is passive and automatically responds to the conditioned stimulus. Operant conditioning requires the organism to perform a behavior that then gets reinforced or punished actively. The organism operates on the environment.
• Involuntary vs. voluntary : Classical conditioning works with involuntary, reflexive responses like salivation, blinking, etc. Operant conditioning shapes voluntary behaviors that are controlled by the organism, like pressing a lever.
• Association vs. reinforcement : Classical conditioning relies on associating stimuli in order to create a conditioned response. Operant conditioning depends on using reinforcement and punishment to increase or decrease voluntary behaviors.

Learning Check

• In Ivan Pavlov’s famous experiment, he rang a bell before presenting food powder to dogs. Eventually, the dogs salivated at the mere sound of the bell. Identify the neutral stimulus, unconditioned stimulus, unconditioned response, conditioned stimulus, and conditioned response in Pavlov’s experiment.
• A student loves going out for pizza and beer with friends on Fridays after class. Whenever one friend texts the group about Friday plans, the student immediately feels happy and excited. The friend starts texting the group on Thursdays when she wants the student to feel happier. Explain how this is an example of classical conditioning. Identify the UCS, UCR, CS, and CR.
• A college student is traumatized after a car accident. She now feels fear every time she gets into a car. How could extinction be used to eliminate this acquired fear?
• A professor always slams their book on the lectern right before giving a pop quiz. Students now feel anxiety whenever they hear the book slam. Is this classical conditioning? If so, identify the NS, UCS, UCR, CS, and CR.
• Contrast classical conditioning and operant conditioning. How are they similar and different? Provide an original example of each type of conditioning.
• How could the principles of classical conditioning be applied to help students overcome test anxiety?
• Explain how taste aversion learning is an adaptive form of classical conditioning. Provide an original example.
• What is second-order conditioning? Give an example and identify the stimuli and responses.
• What is the role of extinction in classical conditioning? How could extinction be used in cognitive behavioral therapy for anxiety disorders?

Bouton, M. E., Mineka, S., & Barlow, D. H. (2001). A modern learning theory perspective on the etiology of panic disorder .  Psychological Review ,  108 (1), 4.

Bremner, J. D., Southwick, S. M., Johnson, D. R., Yehuda, R., & Charney, D. S. (1993). Childhood physical abuse and combat-related posttraumatic stress disorder in Vietnam veterans.  The American journal of psychiatry .

Brewer, W. F. (1974). There is no convincing evidence for operant or classical conditioning in adult humans.

Carter, B. L., & Tiffany, S. T. (1999). Meta‐analysis of cue‐reactivity in addiction research.  Addiction, 94 (3), 327-340.

Davey, B. (1983). Think aloud: Modeling the cognitive processes of reading comprehension.  Journal of Reading, 27 (1), 44-47.

Dugdale, N., & Lowe, C. F. (1990). Naming and stimulus equivalence.

Garcia, J., Ervin, F. R., & Koelling, R. A. (1966). Learning with prolonged delay of reinforcement. Psychonomic Science, 5 (3), 121–122.

Garcia, J., Kimeldorf, D. J., & Koelling, R. A. (1955). Conditioned aversion to saccharin resulting from exposure to gamma radiation.  Science, 122 , 157–158.

Hall, G. (2022). Extinction of conditioned flavor preferences.  Journal of Experimental Psychology: Animal Learning and Cognition .

Logan, C. A. (2002). When scientific knowledge becomes scientific discovery: The disappearance of classical conditioning before Pavlov .  Journal of the History of the Behavioral Sciences ,  38 (4), 393-403.

Lovibond, P. F., & Shanks, D. R. (2002). The role of awareness in Pavlovian conditioning: empirical evidence and theoretical implications.  Journal of Experimental Psychology: Animal Behavior Processes ,  28 (1), 3.

Milad, M. R., Pitman, R. K., Ellis, C. B., Gold, A. L., Shin, L. M., Lasko, N. B.,…Rauch, S. L. (2009). Neurobiological basis of failure to recall extinction memory in posttraumatic stress disorder.  Biological Psychiatry, 66 (12), 1075–82.

Pavlov, I. P. (1897/1902).  The work of the digestive glands . London: Griffin.

Thanellou, A., & Green, J. T. (2011). Spontaneous recovery but not reinstatement of the extinguished conditioned eyeblink response in the rat.  Behavioral Neuroscience ,  125 (4), 613.

Watson, J. B. (1913).  Psychology as the behaviorist views it .  Psychological Review, 20 , 158–177.

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Watson, J. B. (1924).  Behaviorism . New York: People’s Institute Publishing Company.

Watson, J. B., & Rayner, R. (1920).  Conditioned emotional reactions .  Journal of experimental psychology, 3 (1), 1.

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Introduction to Pavlovian Conditioning: Part 1

An object touches an infant's lips and she begins sucking. A child opens the window of a car and the blast of wind causes him to blink. The cutting of onions produces tears in the eyes of a cook. In all of these examples, a stimulus reliably produces a change in behavior. Technically the stimulus is said to elicit the response, and the relation between the stimulus and response is called a reflex. More specifically, it is an unconditioned reflex because it does not depend upon any prior learning. The stimulus is called an unconditioned stimulus (US) and the response is called an unconditioned response (UR) . For more examples of unconditioned reflexes, see Table 1 . All of these "prewired" stimulus-response connections presumably evolved because of their survival value for the individual.

Pavlovian (or Respondent or Classical) Conditioning builds on the unconditioned reflex. Pavlov (1927/1960) studied unconditioned reflexes with dogs. He found that placing meat powder in a dog's mouth (US) elicits salivation (UR). The conditioning part of his experiment involved pairing various innocuous stimuli with the food, such that they preceded food delivery. The fascinating result was that after a number of these pairings, the mere presentation of the paired stimulus elicited salivation.

For example, the sound of a bell elicits very little to no responding; for this reason it is referred to as neutral stimulus (NS) . In Pavlov's experiment, a bell was paired with food presentation. The result was that the bell came to produce a reliable change in behavior, salivation. This new relation is called a conditioned reflex . It is "conditioned" in the sense that it depends on a prior relation between the bell and the food.

A previously neutral stimulus, the bell, became an eliciting stimulus. Technically, at this point it is referred to as a conditioned stimulus (CS) and the salivation resulting from it is said to be the conditioned response(CR) . Pavlov's experiment is illustrated in Figure 1 .

The bell will remain an eliciting stimulus as long as it continues to be paired with the food. If this pairing stops, the bell will return to its neutral status and no longer reliably produce salivation. This phenomenon is known as respondent extinction .

Pavlovian Conditioning is often involved in emotions. In a frequently cited experiment ( Watson & Rayner, 1920 ), an infant boy named Albert was exposed to the sound of striking a suspended steel bar with a hammer. This sound (US) elicited fear-like responses such as crying (UR). Presentations of a white rat reliably preceded this sound; eventually the white rat itself (CS) was sufficient to elicit crying (CR). Albert was not afraid of white rats prior to the experiment; his fear of white rats, or a white rat phobia, developed during the course of the experiment due Pavlovian Conditioning.

Table 1 . Examples of Unconditioned Reflexes (adapted from Grant & Evans, 1994 p. 379)

Figure 1 . Illustration of Pavlov's conditioning experiment (adapted from Grant & Evans, 1994 ).

Ivan Pavlov and the Theory of Classical Conditioning

Pavlov’s experiment

Ivan Pavlov, a Russian physiologist, was carrying out research regarding how dogs salivated in the presence of food. One day, while working on this experiment, he noticed that the dogs began to salivate before he had even brought the food out. Simply s ubjecting the dogs to the conditions of the experiment was enough to provoke this reaction in them.

Pavlov concluded that his dogs had somehow associated the experiment with the imminent introduction of food. In order to unravel the mysteries of these new findings, Pavlov began to design a series of experiments. His goal was to test his hypothesis that when we present two stimuli contingently, an association can take place.

• Jorge Mallea 3 ,
• Javier Bustamante 4 ,
• Gonzalo Miguez 5 &
• Mario A. Laborda 5  

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Introduction

Classical or Pavlovian conditioning is a type of learning where two or more events of the environment are associated. This type of learning helps organisms to organize their behavior and represent their world. In a classic experiment, Pavlov ( 1927 ) discovered that a dog would salivate to the presence of a sound if this sound was previously presented contiguously with food powder. Pavlov called the food powder an unconditioned stimuli (US) that evoked a response by its own, which he called an unconditioned response (UR). The sound was originally a neutral stimulus that did not produce any relevant response, but after being presented with the food, the sound became a conditioned stimulus (CS), which elicited a conditioned response (CR). To Pavlov, this response was “conditional” to the unconditioned stimulus, thereby the name. The study of classical conditioning has changed since Pavlov’s years; we now know that classical conditioning is involved in much more than only...

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Mallea, J., Bustamante, J., Miguez, G., Laborda, M.A. (2019). Classical Conditioning. In: Vonk, J., Shackelford, T. (eds) Encyclopedia of Animal Cognition and Behavior. Springer, Cham. https://doi.org/10.1007/978-3-319-47829-6_1214-1

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Ever Heard of Pavlov’s Dog? Here’s How Classical Conditioning Works

01.01.2022 • 9 min read

Zuriel van Belle

Subject Matter Expert

This article provides a quick and easy guide to understand classical conditioning in psychology with definitions, key terms, and examples.

In This Article

What is Classical Conditioning?

How classical conditioning works, classical conditioning vs. operant conditioning, 4 examples to help you understand classical conditioning.

Does the phrase “Pavlov’s dogs” ring a bell? Ivan Pavlov, a Russian physiologist, made a massive contribution to the psychology of learning through the accidental discovery of what we now call classical conditioning.

Classical conditioning is unconscious learning through association.

Pavlov’s Research

Pavlov’s work as a physiologist focused on the digestive system. Some of his research involved implanting saliva-collecting tubes in dogs’ cheeks and measuring how much saliva the dogs produced when they ate various foods. We all salivate when there is food in our mouths; there is no learning needed because it just happens naturally. (Note: When it comes to research, be sure to understand the difference between quantitative and qualitative research .)

What made Pavlov’s research exceptional is he discovered that the dogs began to salivate:

When they saw the food

When they saw their food bowl

When they simply heard an experimenter approaching.

Pavlov was fascinated by this observation, naming the salivation response to food “psychic secretions.”

Like any good scientist, Pavlov decided to put his observations to a more formal test. Pavlov designed experiments in which he conditioned the dogs to salivate to a number of stimuli, including the ringing of a bell. He started by ringing the bell when he gave meat powder to the dogs. After a while, Pavlov and his team could simply ring the bell without any meat powder present, and the dogs would still salivate in anticipation of the meat powder.

While Pavlov was not a psychologist, his early research on classical conditioning made a huge impact on the psychology of learning. Psychologist John B. Watson built upon Pavlov’s discoveries and popularized behaviorism.

Behaviorism

Behaviorism is a school of thought in psychology that focuses on the observable behavior of humans and animals.

Behaviorists view behavior through a stimulus-response lens and do not rely on hidden psychological processes in their analyses. Behaviorists like Watson believe that an individual is primarily shaped by their environment. Classical conditioning was foundational to the development of behaviorism, offering a clear mechanism by which behavior can be changed through reflexes and associations alone.

The key mechanisms of classical conditioning are stimuli and responses.

A stimulus is something that elicits a response.

A response is the change caused by a stimulus.

Before Conditioning

Before conditioning occurs, there are unconditioned stimuli (UCS) and unconditioned responses (UCR); they are labeled unconditioned because they happen reflexively, they are not conditioned.

In Pavlov’s experiment, the meat powder is the unconditioned stimulus, and the salivation is the unconditioned response. Remember, prior conditioning is not required for a dog to salivate when you put meat powder in its mouth.

During Conditioning

During conditioning, a neutral stimulus (NS) is introduced.

A neutral stimulus (NS) is something that does not elicit a response on its own.

In Pavlov’s experiment, the neutral stimulus is the ringing of the bell. To condition the dogs to the bell, Pavlov paired the meat powder (UCS) with the bell (NS). Over time, the neutral stimulus started to elicit the salivation response in the dogs.

The process of conditioning (or acquisition) can take many pairings of an unconditioned stimulus with a neutral stimulus or very few, depending on the particular stimulus and response. Acquisition can take very little time — as low as five seconds — or it can take many hours.

After Conditioning

After conditioning, the neutral stimulus becomes the conditioned stimulus (CS); the bell now elicits salivation just like the meat powder does. A conditioned stimulus (CS) is any stimulus that elicits a response after repeated pairings with an unconditioned stimulus (UCS) . The salivation becomes the conditioned response (CR) — a response to a previously neutral stimulus.

To recap, classical conditioning begins with an unconditioned stimulus and an unconditioned response. Let’s take the example of squinting when there are bright lights on. The unconditioned stimulus is the bright light, and the squinting is the unconditioned response.

If we pair a neutral stimulus, like a button being pushed, with the bright light many times, then the neutral stimulus will become a conditioned stimulus. Then, when someone pushes the button (now a conditioned stimulus), a person will squint (the conditioned response), whether the bright light is turned on or not.

Second-Order Conditioning

Imagine you want to keep going with the bright light example above. Now, you start pairing the push of a button (now the conditioned stimulus) with a chime (a new neutral stimulus). After numerous pairings, the chime might also elicit squinting. This pairing of a new neutral stimulus with a conditioned stimulus to elicit the initial conditioned response (in this case, squinting) is called second-order conditioning (or sometimes higher-order conditioning).

How far can conditioning go? Usually, it won’t go further than a second neutral stimulus. Beyond that, the association with the initial stimulus and response deteriorates too much.

You might be wondering, once you’ve conditioned a response, are you stuck with it? Thankfully, no. (Imagine those poor dogs salivating at the sounds of bells for the rest of their lives with no meat powder in sight).

If a researcher continued to ring the bell for Pavlov’s dogs without presenting meat powder, the dogs' salivation would become weaker and eventually disappear. That disappearance after exposure to the conditioned stimulus (without the unconditioned stimulus) is called extinction .

Classical conditioning is a bedrock of behaviorism and a critical part of the psychology of learning. Be careful though. Operant conditioning is another important concept, which at first glance, could be easy to confuse with classical conditioning.

Operant Conditioning

The key difference between classical and operant conditioning is that classical conditioning is involuntary and operant conditioning is voluntary.

Operant conditioning changes behavior through reinforcement and punishment.

Think of how you might train your dog to sit. Typically, you lead your dog into a sitting position with a tasty treat (or catch it already sitting) and reinforce the behavior with a treat. As your dog understands what you want, you can add the command “sit.” Over time, the dog learns that when you ask it to sit and it obeys, it will get a cookie. This is one way that operant conditioning works.

Operant conditioning can also work through punishment — but keep in mind that punishment usually doesn’t last long as a teaching tool.

Imagine your dog likes to chew on your favorite pair of shoes. You could make a loud, unpleasant noise each time he does so to “punish” him for the behavior and decrease the likelihood that he will chew on your shoes again. However, research suggests you’d be better off, in the long run, rewarding him when he chews on his bone.

The Difference

Classical conditioning is distinct from operant conditioning. Based on the classical conditioning definition, classical conditioning is all about reflexes and instinctual responses. Conditioning a dog to salivate to a bell is an involuntary process. If you’ve ever asked your dog to sit for a treat when there is meatloaf on the table, you know that operant conditioning is voluntary. This means the dog is more likely to obey if you’ve reinforced sitting many times, but there’s no guarantee.

Now that we understand the basics of classical conditioning. Let’s dive deeper into some classical conditioning examples and how this conditioning affects us in our daily lives.

1. Fear Response

Examples of classical conditioning run the gamut from benign to fairly dark. John B. Watson explored how to classically condition fear. In a now-famous study, Watson conditioned a small child, “Little Albert,” to fear a number of neutral stimuli.

One of Watson’s most famous experiments with Little Albert involved a white rat. In the experiment, he gave Little Albert a white rat to play with (a neutral stimulus). Then, Watson would suddenly clash a hammer against a metal bar right behind poor Little Albert (the unconditioned stimulus). Little Albert, predictably, would feel frightened and cry (the unconditioned stimulus). With enough repetitions, just seeing the white rat would cause Little Albert to become frightened and to cry.

This conditioning was so effective that Little Albert displayed stimulus generalization , where similar items evoke the same conditioned response of fear. So just like with the white rat, Little Albert was fearful of a white rabbit, a white furry coat, and a Santa Claus mask.

It is important to note that Watson’s research is considered completely unethical by contemporary research standards.

Post-traumatic stress disorder (PTSD) , a disorder characterized by exposure to a traumatic event. Many researchers consider intense prolonged distress, as a result of this exposure, to have a classical conditioning component.

During a traumatic event, environmental factors can become conditioned stimuli. For example, if someone experienced a traumatic event on a bridge, they might feel fear, anxiety, and have PTSD symptoms when they are near bridges, reminded of bridges, or see bridges on television. In this case, the bridges are a neutral stimulus that has become a conditioned stimulus because of the traumatic event.

3. Taste Aversions

Taste aversion is a specific (and unpleasant) type of classical conditioning that you may have experienced. Imagine this scenario: you drink a large cup of tomato juice at lunch. A couple of hours later, you start to feel very nauseated and unwell. The next time someone offers you tomato juice, you feel nauseated and unwell again and don’t want to be anywhere near that tomato juice. In this scenario, you’ve developed a taste aversion.

Taste aversion is an interesting form of classical conditioning because you can be conditioned from a single event, even if nausea occurs hours after consuming a particular food. Even more interesting is that the food does not have to be the cause of nausea for the conditioning to occur. Maybe you just happened to get a stomach bug and drink tomato juice on the same day.

Why is taste aversion such a strong conditioner? Researchers think it might have to do with our evolutionary history. You can probably imagine how important it is for survival to link something that makes you sick with something you consumed. For example, it is advantageous to get nauseous after eating a few toxic berries and, through the mechanisms of taste aversion, avoid those berries in the future. This is better than trying the berries again and again and possibly consuming so many that you do permanent damage to your body or die.

4. Classical Conditioning in Daily Life

On a lighter note, classical conditioning is also at work in our everyday lives.

Imagine you have a habit of eating slices of lemon. You cut up a lemon for lemonade, grab a slice, and pop it in your mouth, and your mouth puckers and salivates as you eat the lemon. If you do this enough times, you might find that even seeing or thinking about a lemon makes your mouth pucker and water. (Perhaps your mouth even watered reading this passage because of a preexisting conditioned response around lemons.)

This everyday conditioning can happen with all sorts of things.

Spa Weekend

One last example: imagine you visit a spa every weekend (lucky you!). At the spa, they have oil diffusers placed elegantly about with a mix of wonderful floral scents. You always get a relaxing massage in this fragrant setting. After a while, you might find that just smelling their proprietary blend of fragrant botanicals makes you feel relaxed.

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• 1 Cornell University
• 2 A.T. Still University
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• 4 University Hospital Lewisham
• PMID: 29262194
• Bookshelf ID: NBK470326

Learning is the process by which new knowledge, behaviors, attitudes, and ideas are acquired. Learning can occur through both unconscious and conscious pathways. Classical conditioning is one of those unconscious learning methods and is the most straightforward way in which humans can learn. Classical conditioning is the process in which an automatic, conditioned response is paired with specific stimuli. Although Edwin Twitmyer published findings pertaining to classical conditioning one year earlier, the best-known and most thorough work on classical conditioning is accredited to Ivan Pavlov, a Russian physiologist born in the mid-1800s. Pavlov had such a great impact on the study of classical conditioning that it is often referred to as Pavlovian conditioning.

Pavlov’s Experiment

Classical conditioning was stumbled upon by accident. Pavlov was conducting research on the digestion of dogs when he noticed that the dogs’ physical reactions to food subtly changed over time. At first, the dogs would only salivate when the food was placed in front of them. However, later they salivated slightly before their food arrived. Pavlov realized that they were salivating at the noises that were consistently present before the food arrived; for example, the sound of a food cart is approaching.

To test his theory, Pavlov set up an experiment in which he rang a bell shortly before presenting food to the dogs. At first, the dogs elicited no response to the bells. However, eventually, the dogs began to salivate at the sound of the bell alone.

To understand classical conditioning, it is essential to be familiar with the following terms. A neutral stimulus is a stimulus that at first elicits no response. Pavlov introduced the ringing of the bell as a neutral stimulus. An unconditioned stimulus is a stimulus that leads to an automatic response. In Pavlov’s experiment, the food was the unconditioned stimulus. An unconditioned response is an automatic response to a stimulus. The dogs salivating for food is the unconditioned response in Pavlov’s experiment. A conditioned stimulus is a stimulus that can eventually trigger a conditioned response. In the described experiment, the conditioned stimulus was the ringing of the bell, and the conditioned response was salivation.

It is important to note that the neutral stimulus becomes the conditioned stimulus. Furthermore, it is important to realize that the unconditioned response and the conditioned response are the same except for which stimulus they are elicited by. In this case, salivation was the response, but the unconditioned response was triggered by food, whereas the conditioned response was triggered by the bell which indicated the coming of food.

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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

StatPearls [Internet].

Classical conditioning.

Ibraheem Rehman ; Navid Mahabadi ; Terrence Sanvictores ; Chaudhry I. Rehman .

Affiliations

Last Update: August 14, 2023 .

• Introduction

Learning is the process by which new knowledge, behaviors, attitudes, and ideas are acquired. Learning can occur through both unconscious and conscious pathways. Classical conditioning is one of those unconscious learning methods and is the most straightforward way in which humans can learn. Classical conditioning is the process in which an automatic, conditioned response is paired with specific stimuli. Although Edwin Twitmyer published findings pertaining to classical conditioning one year earlier, the best-known and most thorough work on classical conditioning is accredited to Ivan Pavlov, a Russian physiologist born in the mid-1800s. Pavlov had such a great impact on the study of classical conditioning that it is often referred to as Pavlovian conditioning. [1] [2] [3]

Pavlov’s Experiment

Classical conditioning was stumbled upon by accident. Pavlov was conducting research on the digestion of dogs when he noticed that the dogs’ physical reactions to food subtly changed over time. At first, the dogs would only salivate when the food was placed in front of them. However, later they salivated slightly before their food arrived. Pavlov realized that they were salivating at the noises that were consistently present before the food arrived; for example, the sound of a food cart is approaching.

To test his theory, Pavlov set up an experiment in which he rang a bell shortly before presenting food to the dogs. At first, the dogs elicited no response to the bells. However, eventually, the dogs began to salivate at the sound of the bell alone.

To understand classical conditioning, it is essential to be familiar with the following terms. A neutral stimulus is a stimulus that at first elicits no response. Pavlov introduced the ringing of the bell as a neutral stimulus. An unconditioned stimulus is a stimulus that leads to an automatic response. In Pavlov’s experiment, the food was the unconditioned stimulus. An unconditioned response is an automatic response to a stimulus. The dogs salivating for food is the unconditioned response in Pavlov’s experiment. A conditioned stimulus is a stimulus that can eventually trigger a conditioned response. In the described experiment, the conditioned stimulus was the ringing of the bell, and the conditioned response was salivation.

It is important to note that the neutral stimulus becomes the conditioned stimulus. Furthermore, it is important to realize that the unconditioned response and the conditioned response are the same except for which stimulus they are elicited by. In this case, salivation was the response, but the unconditioned response was triggered by food, whereas the conditioned response was triggered by the bell which indicated the coming of food.

Pavlov recorded several phenomena associated with classical conditioning. He found that the rate of acquisition, the initial stages of learning, depended on the noticeability of the stimulus and the time in between the introduction of the neutral stimulus and the unconditioned stimulus. In Pavlov’s experiment, this would translate to the time in between the bell ringing and the presentation of food. Second, Pavlov observed that the conditioned response was vulnerable to extinction. If the conditioned stimulus is continuously supplied in the absence of the unconditioned stimulus, then the conditioned response becomes weaker and weaker until it disappears. In Pavlov’s experiment, this would translate to Pavlov ringing the bell without giving food to the dogs. Eventually, the dogs would stop salivating at the sound of the bell. However, spontaneous recovery was also observed. Even if a substantial amount of time had passed, the conditioned response would easily recover if the neutral stimulus and the unconditioned stimulus were paired again. Lastly, he found that stimulus generalization and stimulus discrimination can occur. Stimulus generalization occurs when the dog can respond to stimuli that are similar to the conditioned stimulus. For example, if Pavlov’s dogs salivated at the sound of another ringing sound such as a cell phone ringing, that would be stimulus generalization. Stimulus discrimination, on the other hand, is being able to differentiate between similar stimuli and respond only to the correct stimuli. [4] [5] [6] [7]

• Issues of Concern

People can use classical conditioning to exploit others for their gain. A prominent example of this occurs in advertising. The advertiser generally attempts to get consumers to associate their product with a particular response or feeling so they are more likely to buy the product. Advertisers can use music or mouth-watering food in their ads to create an association with their product. These types of associations can lead to increased spending as well as poor eating habits especially if the product is unhealthy food. 

• Clinical Significance

Most psychologists now agree that classical conditioning is a basic form of learning. Furthermore, it is well-known that Pavlovian principles can influence human health, emotion, motivation, and therapy of psychological disorders. There are many clinically related uses of classical conditioning. For example, former drug users often have a craving when they are in a drug-related environment or around people that they associate with previous highs. Drug counselors often advise these people to stay away from settings that could trigger a desire to take drugs again. Also, it has been proven that classical conditioning can even affect the human immune system. When a particular taste accompanies a drug that influences an immune response, sometimes the taste itself can induce the immune response at a later time. Another example can be found in the overcoming of phobias. One patient, who had feared getting into an elevator for 30 years, forced herself to enter 20 elevators a day. After 10 days, her fear had almost completely vanished.

O.H Mowrer discovered that certain behaviors can be reconditioned when he successfully developed a therapy for bed-wetters. In his therapy, the child would sleep on a liquid-sensitive pad connected to an alarm. Once moisture was detected, the alarm would go off. After repetition, bladder relaxation became associated with waking up and 75% of the time, frequent bed-wetters were healed and longer wet the bed while they slept.

Another example of an effective therapy that is used to cure phobias is counterconditioning, which pairs the trigger stimulus with a response that is contrary to fear. Two counterconditioning techniques that have been proven to be effective are exposure therapy and aversive therapy. In general, exposure therapies are therapies that expose people to what scares them. Two types of exposure therapies are systematic desensitization and virtual reality exposure therapy. In systematic desensitization, a pleasant, relaxed state is associated with increasing anxiety-triggering stimuli. This therapy is common in the treatment of phobias. Virtual reality exposure follows the same concept as general exposure therapy but uses virtual reality to do instead of real-life situations. Aversive conditioning has the goal of substituting a negative response for a positive response to a harmful stimulus. This is essentially the reverse of systematic desensitization in which a positive response is replaced with a negative response to a harmless stimulus. One common example of aversive conditioning is mixing alcohol with an extremely bitter taste or lacing fingernails with something that causes severe nausea. The problem with this therapy is that patients can differentiate between situations inside and outside of the psychiatrist’s office. An alcoholic understands that if he drinks alcohol, it will normally not have that bitter taste. For this reason, a combination of conditioning therapies is the best approach to treat certain issues. [8] [9]

• Other Issues

A combination of both behavior modification therapy with medications can lead to better clinical outcomes than if either option is used alone. Some studies show enhanced outcomes when certain drugs are used in the psychological treatment of anxiety disorders and even post-traumatic stress disorders. Despite the clinical efficacy of these studies, it should be noted that each individual can have a different treatment plan that is optimal to only them. Some people might respond better to only therapy or medications rather than a combination of both. Furthermore, combination treatments can be more of a "mix and match" treatment where two patients can have similar amounts of treatment success but use different medications and therapy options. [10] [11] [12]

• Enhancing Healthcare Team Outcomes

Classical conditioning concepts are integrated into the design of health-related interventions (i.e. modeling, reinforcement, expectancies, and cues to action). Cohesiveness and consistency of the patient/ interprofessional team implementing these types of interventions are important factors for success. The interprofessional healthcare team consists of diagnosticians, medication experts, prescribers, and other members who tend to the everyday needs of the patient. Cohesiveness and communication become especially important for the extinguishing of addictive behaviors such as drug use, smoking, or drinking alcohol. Since relapse is always a possibility, proper protocols should be in place to help re-extinguish the behavior if necessary. However, these protocols mainly depend on the patient's honesty and willingness to seek out help. Additionally, the interprofessional team can increase conditioning success by involving the patient's friends and family. They not only provide emotional support for the patient but can also provide updates to the interprofessional team when needed. [13] [14]

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Disclosure: Ibraheem Rehman declares no relevant financial relationships with ineligible companies.

Disclosure: Navid Mahabadi declares no relevant financial relationships with ineligible companies.

Disclosure: Terrence Sanvictores declares no relevant financial relationships with ineligible companies.

Disclosure: Chaudhry Rehman declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

• Cite this Page Rehman I, Mahabadi N, Sanvictores T, et al. Classical Conditioning. [Updated 2023 Aug 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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What’s Wrong With This Picture? Just About Everything

• Pavlovian Conditioning

The diagram below, or something like it, is frequently used to introduce students to the type of learning research pioneered by Russian physiologist Ivan Pavlov. Pavlovian conditioning remains a popular and important form of learning more than a century after Pavlov accepted the Nobel Prize in 1904 for his work on the digestive system. Unfortunately, this diagram does not convey why Pavlovian conditioning remains a core phenomenon in psychology. The diagram also perpetuates numerous misconceptions about Pavlovian conditioning.  

Pavlov did not ring a bell as a conditioned stimulus (CS). The initial experiments on salivary conditioning were carried out by Pavlov’s research assistants, Sigizmund Vul’fson and Anton Snarskii, who used a visual rather than auditory cue as the CS. The experimental protocol was relatively simple. A substance such as dry food, sand, or sour water was placed in a dog’s mouth on repeated trials. These substances elicited salivation without training, or unconditionally. The novel finding was that after a number of trials, the dogs started salivating at the sight of the substance that was to be placed in their mouth. The source of the visual CS in the original experiments is highly significant and has broad implications for how Pavlovian conditioning occurs in the natural environment.  

In a typical diagram, the CS (in this case, a bell) is characterized as a “neutral” stimulus that is initially unrelated to the unconditioned stimulus (US; in this case, a steak). However, that was not the case in Vul’fson’s and Snarskii’s experiments. The dogs in their experiments learned a relationship between different features of the substances or objects that were placed in their mouths. Those objects had features that elicited salivation unconditionally and visual features that came to elicit salivation through association with the US features. The fact that the CS and the US were features of the same object ensured that the two stimuli would be experienced in close temporal proximity, which facilitated their association.  

Pavlovian conditioning requires repeated pairings of a CS with a US. Such pairings occur outside the lab only if there is an inherent relationship between the CS and the US. Thus, Pavlovian conditioning in the natural environment involves the type of arrangement that Vul’fson and Snarskii created. Most naturally occurring examples of Pavlovian conditioning involve learning about a CS that has an inherent or pre-existing relation to the US and therefore is not “neutral” or “arbitrary.” When a child becomes fearful of dogs after a dog bite, they are forming the type of within-object association that Vul’fson and Snarskii originally demonstrated. One feature of the dog (its visual appearance or bark) comes to elicit fear because it is associated with other aspects of the dog (the dog’s bite). Social phobias, fear of public speaking, and fear of intimacy are all learned in the same fashion: The presence of others becomes a signal, or CS, for an aversive outcome, or US, in certain social situations.   

Most naturally occurring examples of Pavlovian conditioning involve learning about a CS that has an inherent or pre-existing relation to the US and therefore is not “neutral” or “arbitrary.”

Learning to link together different features of an object or situation extends the scope of Pavlovian mechanisms well beyond conditioned salivation. However, the emphasis on conditioned salivation in teaching about Pavlovian conditioning has promoted the misconception that Pavlovian learning is limited to glandular responses that are of little psychological interest. B. F. Skinner reflected that line of thinking in his landmark book, Science and Human Behavior (1953), in which he seemed to take pleasure in Bernard Shaw’s irreverent description of Pavlov’s work as just having to do with “the spittle of dogs.” Unfortunately, Skinner’s take on Pavlovian conditioning remains evident in contemporary books on behavior analysis. The latest edition of the comprehensive text Applied Behavior Analysis (Cooper et al., 2020), for example, includes Skinner’s claim that “reflexes, conditioned or otherwise, are mainly concerned with the internal physiology of the organism” (1953, p. 59). This claim ignores research on different forms of Pavlovian conditioning such as sign tracking, goal tracking, sexual conditioning, and conditioning of various forms of defensive behavior that promote effective interactions with the external environment rather than “internal physiology.”   

The common diagram of Pavlovian conditioning also promotes the misconception that a discrete conditioned reflex is the primary outcome of Pavlovian learning. However, Pavlovian conditioning is also involved in the learning of emotions, preferences and aversions, and likes and dislikes that can be expressed in a variety of different ways. In many cases, moreover, the most important outcome of conditioning is not the emergence of a new response to the CS but the capacity of the CS to change how the individual responds to the US. The conditioned salivation that Vul’fson and Snarskii observed was important because it enabled the dog to respond more effectively to the dry food or sand that was about to go in its mouth. In a similar fashion, studies have shown that conditioned stimuli enable organisms to cope more quickly and more effectively with a variety of different unconditioned stimuli such as food, an aggressive intruder, or a potential sexual partner. Conditioned modifications of the response to the US are also critical when the US is the administration of a drug: Learning to anticipate the drug allows individuals to make homeostatic compensatory adjustments that reduce the drug’s effects. These conditioned compensatory responses are missing if the drug is taken in the absence of the usual drug-predictive cues, and that can result in drug overdose. Thus, rather than being concerned just with the “spittle of dogs,” Pavlovian conditioning can be a matter of life or death.  

We have learned a lot since the pioneering experiments of Vul’fson and Snarskii. No one diagram can be expected to accurately capture the richness of contemporary knowledge about Pavlovian conditioning. However, I hope that diagrams can be developed that will at least represent the original experiment correctly and show Pavlovian conditioning as the pervasive natural learning phenomenon that it is rather than a creation of laboratory scientists who misleadingly label a CS as “neutral” or “arbitrary.”

Feedback on this article? Email [email protected] or scroll down to comment .

Thank you for a very informative article and for “setting the record straight” on the original procedures used in Pavlov’s Lab. I may have missed it but, is there any reference cited that was used to provide details of the original research (assistant’s names, stimuli used, etc). I would be very interested in getting any available material on Pavlov’s original work (most published in Russian or German perhaps Journals? ) Thank you

The most important response that is conditioned during classical conditioning is not one of the simple physiological reflexes, but the emotional reaction to signals that appear to predict something good or something bad. In the case of food, this reflex is enthusiasm (positive excitement plus approach tendencies). In natural situations, this response helps to emit unlearned and learned responses to get and consume the food, and it remains the most important part of the conditioned reflex. In classical conditioning, however, the dog is restrained, cannot emit such approach responses. Hence, these are to no avail and are extinguished in the course of a number of trials, and nothing remains but the physiological salivary reflex, which are still useful because they help with swallowing and digesting the food.

In the case of negative classical conditioning, the main thing conditioned is the emotional fear of a repetition of the shock, not the physiological reflexes to the shock. In natural situations, this fear response does much to motivate potentially effective escape and avoidance responses.

Psychological instruction would be helped if these anticipatory emotional responses, preparing the subject for instrumental action toward the challenge, will be stressed instead of minor physiological responses, when classical conditioning is discussed.

The point about CS not being neutral, but having biological significance in of itself, points to sensory modality and prior experiences. A “neutral” light CS has photons, or waves, exciting the underlying neuroanatomy, neurochemistry and physiology. And depending on prior experience with different light variables, including its intensity and internal spread of activation, the light would no longer be neutral- given its internal association / spread to affectively – biologically significant circuitry and prior external associations- being that light is everywhere. A neutral state such as texas would no longer be considered neutral had someone would had been harmed and kidnapped there, for example.

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About the Author

Michael Domjan , an APS Fellow, is professor of psychology at the University of Texas at Austin and author of Principles of Learning and Behavior (7th edition, Cengage, 2015) and Essentials of Conditioning and Learning (4th edition, American Psychological Association, 2018).

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Ivan Petrovich Pavlov and conditioned reflexes

Who was ivan pavlov (1849-1936).

For his original work in this field of research, Pavlov was awarded the Nobel Prize in Physiology or Medicine in 1904. By then he had turned to studying the laws on the formation of conditioned reflexes, a topic on which he worked until his death in 1936. His discoveries in this field paved the way for an objective science of behavior.

Pavlov's drooling dogs

Pavlov became interested in studying reflexes when he saw that the dogs drooled without the proper stimulus. Although no food was in sight, their saliva still dribbled. It turned out that the dogs were reacting to lab coats. Every time the dogs were served food, the person who served the food was wearing a lab coat. Therefore, the dogs reacted as if food was on its way whenever they saw a lab coat.

In a series of experiments, Pavlov then tried to figure out how these phenomena were linked. For example, he struck a bell when the dogs were fed. If the bell was sounded in close association with their meal, the dogs learnt to associate the sound of the bell with food. After a while, at the mere sound of the bell, they responded by drooling.

Different kinds of reflexes

Pavlov's discovery was that environmental events that previously had no relation to a given reflex (such as a bell sound) could, through experience, trigger a reflex (salivation). This kind of learnt response is called conditioned reflex, and the process whereby dogs or humans learn to connect a stimulus to a reflex is called conditioning.

Animals generally learn to associate stimuli that are relevant to their survival. Food aversion is an example of a natural conditioned reflex. If an animal eats something with a distinctive vanilla taste and then eats a tasteless poison that leads to nausea, the animal will not be particularly eager to eat vanilla-flavoured food the next time. Linking nausea to taste is an evolutionarily successful strategy, since animals that failed to learn their lesson did not last very long.

Why were Pavlov's findings given so much acknowledgment?

Pavlov's description on how animals (and humans) can be trained to respond in a certain way to a particular stimulus drew tremendous interest from the time he first presented his results. His work paved the way for a new, more objective method of studying behavior.

So-called Pavlovian training has been used in many fields, with anti-phobia treatment as but one example. An important principle in conditioned learning is that an established conditioned response (salivating in the case of the dogs) decreases in intensity if the conditioned stimulus (bell) is repeatedly presented without the unconditioned stimulus (food). This process is called extinction.

Conditioning forms the basis of much of learned human behavior. Nowadays, this knowledge has also been exploited by commercial advertising. An effective commercial should be able to manipulate the response to a stimulus (like seeing a product's name) which initially does not provoke any feeling. The objective is to train people to make the "false" connection between positive emotions (e.g. happiness or feeling attractive) and the particular brand of consumer goods being advertised.

Pavlov's prize

Until Pavlov started to scrutinize this field, our knowledge of how food was digested in the stomach, and what mechanisms were responsible for regulating this, were quite foggy.

In order to understand the process, Pavlov developed a new way of monitoring what was happening. He surgically made fistulas in animals' stomachs, which enabled him to study the organs and take samples of body fluids from them while they continued to function normally.

By Lotta Fredholm, Science Journalist

More about Nobel Laureate Ivan Pavlov

Play the Pavlov's Dog Game

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