Unconditioned Stimulus in Classical Conditioning: Definition & Examples

Using the terminology of the classical conditioning paradigm, the unconditioned stimulus (US) is a stimulus that leads to an automatic response. In other words, the response takes place without any prior learning.

For example, if the smell of your favorite food makes you feel hungry or a cold breeze makes you shiver, the smell of the food and the cold breeze are considered unconditioned stimuli.

They produce an involuntary reaction without you being trained to have that response. Unlike a conditioned stimulus (CS), you do not have to learn to respond to the unconditioned stimulus, but rather the response occurs automatically.

The best-known and most thorough work on classical conditioning was discovered by Ivan Pavlov in the early 1900s in his experiments on the digestive response of dogs.  Pavlov had such a great impact on the study of classical conditioning that it is often referred to as Pavlovian conditioning.

Simply Psychology Logo

In classical conditioning, the conditioned stimulus begins as a neutral stimulus that eventually comes to automatically trigger a conditioned response after becoming associated with an unconditioned stimulus. After the neutral stimulus becomes associated with the unconditioned stimulus, it becomes the conditioned stimulus.

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.

Some other examples of unconditioned stimuli in our everyday lives include an unexpected loud bang causing you to flinch or dust in your nose causing you to sneeze. Unconditioned stimuli lead to natural reactions of our bodies that can help protect us from potential dangers.

What is an example of an unconditioned stimulus?

Pavlovs Dogs Experiment

Ivan Pavlov was the first person to discover the process of classical conditioning. When conducting research on the digestion of dogs, Pavlov noticed that the dogs’ physical reactions to food changed over time.

While at first, the dogs would only salivate when the food was placed in front of them, they eventually began to salivate slightly before their food arrived.

He realized that the dogs were not salivating to the smell or sight of the food in front of them but rather the noises and sites that were consistently present before the food even arrived.

To test his theory further, Pavlov would ring a bell shortly before presenting food to the dogs. At first, this elicited no response from the dogs, but eventually, the dogs learned to associate the sound of the bell with the presentation of the food and they would begin to salivate at the sound of the bell alone.

As mentioned earlier, an unconditioned stimulus is a stimulus that leads to an automatic response. So in Pavlov’s experiment, the food is the unconditioned stimulus and the dogs salivating for food is the unconditioned response.

Salivation occurred automatically and without the dogs” conscious effort when they smelled the food. The food was the unconditioned stimulus because it prompted a reflexive response and required no learning.

Little Albert (Watson & Raynor) Experiment

Behaviorist John B. Watson and graduate student Rosalie Rayner were the first psychologists to apply the principles of classical conditioning to human behavior by showing that emotional reactions could be classically conditioned in people.

Their experiment, known as the case of Little Albert, involved conditioning a phobia in an emotionally stable child.

When Albert was just 9 months old, Watson and Rayner exposed him to a series of stimuli including a white rat, burning newspapers, a monkey, and masks.

At first, Alert showed no fear of any of the stimuli.

However, the next time Albert was exposed to each stimuli, Watson would make a loud noise by hitting a metal pipe with a hammer.

After repeatedly pairing one of the stimuli, the white rat for example, with the loud noise, Albert would begin to expect a loud noise whenever he saw the white rate.

Eventually, Albert would begin to cry from simply seeing the rat. In other words, he was classically conditioned to experience fear at the sight of the rat.

The loud noise is the unconditioned stimulus in this example. When Watson would make the loud noise, Albert would cry. Watson used this unconditioned response to condition Little Albert to fear distinctive stimuli that normally would not be feared by a child (ie: the white rat or the monkey).


Classical conditioning is an effective tool in marketing and advertising. The idea is to create an advertisement that has positive features such as catchy music, bright colors, cute babies, attractive models, or funny spokespeople so that the ad will create an enjoyable response in the person exposed to it.

Thus, when the consumer sees the particular product online or in the store, he/she should experience this positive feeling and be more likely to purchase the product.

In this example, the advertisement serves as the unconditioned stimulus (US), and the enjoyment from watching the advertisement serves as the unconditioned response (UR). Because the product being advertised is mentioned in the advertisement, it becomes associated with the US, and then becomes the conditioned stimulus (CS).

One example of this kind of conditioning is seen in the “Drake Sprite: The Spark Commercial,” a Sprite commercial starring rapper Drake. In this one minute advertisement, Drake is not able to rap very well and is feeling uninspired.

But, when he takes a sip of a Sprite, he is reinvigorated and instantly able to rap again. The unconditioned stimulus is Drake and the conditioned stimulus is drinking Sprite. The conditioned response is thinking that by drinking Sprite you will be refreshed and inspired just like Drake.


According to the theories of classical conditioning, drug-related stimuli can become associated with the rewarding aspects of using.

For example, drug paraphernalia, such as cigarette packets, bongs, and pipes, and environments where drug use occurs can invoke craving and drug-seeking responses in users. For smokers, just the sight of a cigarette packet can invoke the feeling of wanting to smoke.

This paraphernalia are considered the conditioned stimuli and nicotine would be the unconditioned stimulus .

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.

These factors become smoking-related cues. Prolonged use of nicotine creates association between these factors and smoking. This is 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).

In a 2012 study on associative learning in smokers, Marianne Littel found that smokers show pronounced associative learning during a higher-order conditioning experiment in response to neutral cues that are paired with smoking-related stimuli.

In other words, she conditioned smokers to associate smoking with an object that had previously been entirely neutral.


What is the difference between the unconditioned stimulus and the discriminative stimulus?

A discriminative stimulus refers to something, like a person or an event, that precedes a behavioral response. So, the discriminative stimulus comes first and then, the behavior follows as a direct result of this stimulus.

A discriminative stimulus is created when the response is reinforced whereas an unconditioned stimulus is a stimulus that leads to an automatic response without any reinforcement or prior learning.

What is the difference between the unconditioned stimulus and the neutral stimulus?

A neutral stimulus is a stimulus that does not produce an automatic response at first whereas an unconditioned stimulus is quite the opposite – an unconditioned stimulus is a stimulus that does produce an automatic response.

In classical conditioning, the neutral stimulus will become a conditioned stimulus when consistently paired with an unconditioned stimulus.

When it is initially presented, the neutral stimulus has no effect on behavior. However, as it is repeatedly paired with an unconditioned stimulus, it will begin to cause the same response as the unconditioned stimulus.

What is the difference between the unconditioned stimulus and the unconditioned response?

An unconditioned stimulus is a stimulus that leads to an automatic response. An unconditioned response is that automatic response to the stimulus. The dogs salivating for food is the unconditioned response in Pavlov’s experiment.

How does an unconditioned stimulus become a conditioned stimulus?

An unconditioned stimulus becomes a conditioned stimulus after the neutral stimulus becomes associated with the unconditioned stimulus and the subject has learned to associate the stimulus with a given outcome.

Is alcohol an unconditioned stimulus?

Yes, alcohol is an unconditioned stimulus in classical conditioning. The effects of alcohol (intoxication and inhibition) do not have to be learned. They are universal, consistent, and automatic.


Clark, R. E. (2004). The classical origins of Pavlov’s conditioning.  Integrative Physiological & Behavioral Science 39 (4), 279-294.

Gorn, G. J. (1982). The effects of music in advertising on choice behavior: A classical conditioning approach.  Journal of marketing 46 (1), 94-101.

Harris, B. (1979). Whatever happened to little Albert?.  American psychologist 34 (2), 151.

Hawkins, D., Best, R., & Coney, K. (1998.) Consumer Behavior: Building Marketing Strategy (7th ed.). Boston, MA: McGraw-Hill.

Littel, M., Franken, I.H. Electrophysiological correlates of associative learning in smokers: a higher-order conditioning experiment. BMC Neurosci 13, 8 (2012).

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

Pavlov, I. P. (1928). Lectures on conditioned reflexes. (Translated by W.H. Gantt) London: Allen and Unwin.

Pavlov, I. P. (1927). Conditioned Reflexes: An Investigation of the Physiological Activity of the Cerebral Cortex . Translated and edited by Anrep, GV (Oxford University Press, London, 1927).

Pavlov, I. P. (1955). Selected works. Moscow: Foreign Languages Publishing House.

Rehman I, Mahabadi N, Rehman CI. Classical Conditioning . In: StatPearls[Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470326/

Vladtv, YouTube(2010, November). Drake Sprite: The Spark Commercial. Retrieved December 15, 2019, from https://www.youtube.com/watch?v=mh6vHoyBs58 .

Watson, J.B. (1913). Psychology as the behaviorist Views It. Psychological Review, 20, 158-177.

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

Saul Mcleod, PhD

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

Educator, Researcher

Saul Mcleod, Ph.D., is a qualified psychology teacher with over 18 years experience of working in further and higher education.

Julia Simkus

Research Assistant at Princeton University

Undergraduate at Princeton University

Julia Simkus is a Psychology student at Princeton University. She will graduate in May of 2023 and go on to pursue her doctorate in Clinical Psychology.