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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

  1. What is Classical Conditioning?

  2. How Classical Conditioning Works

  3. Classical Conditioning vs. Operant Conditioning

  4. 4 Examples to Help You Understand Classical Conditioning

What is 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 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.

How Classical Conditioning Works

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.

Bright Light (UCS)   ->    Squinting (UCR)
Push of a Button (NS) + Bright Light (UCS)    ->    Squinting (UCR)
Push of a Button (CS)    ->    Squinting (CR)

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 vs. Operant Conditioning

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.

4 Examples to Help You Understand Classical Conditioning

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.

Hammering Sound Against Metal (UCS)    ->    Fearfulness (UCR)
A White Rat (NS) + Hammering Sound Against Metal (UCS)    ->    Fearfulness (UCR)
A White Rat (CS)    ->    Fearfulness (CR)

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.

Traumatic Event (UCS)    ->    Fear and Anxiety (UCR)
A Bridge (NS) + Traumatic Event (UCS)    ->    Fear and Anxiety (UCR)
A Bridge (CS)    ->    Fear and Anxiety (CR)

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.)

The Sour Taste of a Lemon (UCS)   ->   Mouth Puckering and Watering (UCR)
Imagining a Lemon (NS) + The Sour Taste of a Lemon (UCS)   ->   Mouth Puckering and Watering (UCR)
Imagining a Lemon (CS)   ->   Mouth Puckering and Watering (CR)

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.

Massage (UCS)   ->   Relaxation (UCR)
Proprietary Spa Fragrance (NS) + Massage (UCS)   ->   Relaxation (UCR)
Proprietary Spa Fragrance (CS)   ->   Relaxation (CR)

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