What Is Unconditioned Stimulus in Psychology?

The unconditioned response is one part of the class of reflexive behavioral responses. The term unconditional was given because it does not require learning or previous experience. This article will deeply dive into what it is, how it differs from conditioned responses and more.

What Is Unconditioned Stimulus?

When a stimulus is presented to a person, and the response is automatic and unthinking, it is said to be an unconditioned stimulus (US). This means that there is no learning involved in producing the response. The response is produced automatically by a reflex.

For example, if you touch your finger on a hot stove, your hand will immediately jerk away from the heat without any thought or learning involved. You do not have to learn how to avoid touching hot stoves because this reflexive response has been learned through past experiences with hot stoves.

Examples of Unconditioned Stimulus

The best way to learn about the unconditioned stimulus is by looking at an example. Let’s take a look at some examples:

  1. An example of an unconditioned stimulus would be food. When you see or smell food, your body will begin to salivate in anticipation of eating it. It does not need any time to get used to this feeling because it is natural and innate.
  2. Another example would be pain. If you are hit in the arm, your body will naturally react with pain and pull away from the source of pain as a defensive reaction. Once again, there is no need for conditioning in this instance because pain is a natural reaction to being hit and injured.
  3. A dog salivates in response to food. This natural eliciting stimulus is also an example of an unconditioned stimulus (UCS) because it automatically causes salivation.

Types of Unconditioned Stimulus

The unconditioned stimulus can be divided into two categories:

  • Aversive conditioning
  • Appetitive conditioning

Aversive conditioning is a type of learning that occurs when a stimulus (most often an unpleasant one) is paired with a neutral stimulus, and the subject learns to avoid the neutral stimulus. The most common example is pairing a shock with a tone, which will eventually cause the subject to avoid the tone because they associate it with pain or discomfort.

A classic example of aversive conditioning is fear induction. For example, suppose an animal is given electric shocks every time it hears a certain sound (like a dog being shocked every time he barks). In that case, eventually, he will stop barking when he hears that noise because he associates it with pain (even though there’s no physical connection between them).

In contrast, appetitive conditioning is how organisms learn to approach stimuli associated with positive outcomes and avoid those associated with adverse outcomes. This type of learning involves associations between stimuli and outcomes, as opposed to connections between one stimulus and another.

An example of appetitive conditioning would be learning that a bell will predict food or water when hungry or thirsty. This can be done by pairing the bell with food or water or giving the subject a choice between the bell and a plate of food/water (a Pavlovian conditioned response). The subject learns that the bell predicts food/water and salivates upon hearing it (it starts secreting saliva as soon as it hears it).

In short, the two types of conditioning have different effects on behavior because each has a different goal: Aversive conditioning aims at reducing or eliminating particular behaviors. In contrast, appetitive conditioning aims at increasing certain behaviors.

Difference Between Unconditioned Stimulus and Conditioned Stimulus

An unconditioned stimulus (US) is a stimulus that does not require any conditioning. It produces an unconditioned response (UR) which is immediate, reflexive, and unlearned.

In contrast, a conditioned Stimulus (CS) is a stimulus that becomes associated with another stimulus through association learning. For example, when you ring a bell every time your dog gets fed, the sound of that bell will eventually become a conditioned stimulus for your dog when it hears it.

The conditioned response (CR) is a learned response to the conditioned stimulus and occurs only after repeated pairing the two stimuli over time. If you do not pair the bell with feeding your dog, then there will be no conditioned response to the bell because your dog has no previous experience with it.

Pavlov’s Experiment and Classical Conditioning

Pavlov’s experiment is one of the most famous experiments in psychology. It was conducted by Ivan Pavlov, who discovered how conditioned reflexes work.

The experiment involved Pavlov’s dog, which was trained to associate food with a bell. When the food appeared, the dog would salivate in anticipation of it. After several repetitions of this process, Pavlov rang a bell without providing food and noticed that the dog still salivated in anticipation of receiving its meal.

This showed that when a stimulus is repeated frequently enough with another stimulus (such as food), our brains automatically associate the two together so that we respond the same way as we would if both stimuli were presented together. This effect is known as conditioning.

Pavlov’s findings have also been used to explain many other things in psychology, such as why we yawn when someone else does or feel stressed when we see other people get stressed out.

Little Albert Experiment

The Little Albert Experiment is a famous psychology experiment performed by John B. Watson and Rosalie Rayner in 1920. The experiment showed that classical (or Pavlovian) conditioning could be applied to emotional responses. 

In this experiment, a nine-month-old infant dubbed Albert was shown a white rat and other furry animals, which he liked. After several repetitions of the pairings, the infant reacted fearfully to the white rat and other animals. The researchers concluded that he had been conditioned by pairing an initially neutral stimulus with an unconditioned stimulus (the sight of the rabbit) that naturally produced fear in infants.

This experiment aimed to demonstrate how classical conditioning works and how it can be applied to children’s emotional responses.

Unconditioned Stimulus and Unconditioned Response

Classical conditioning is the relationship between the unconditioned stimulus (US) and the unconditioned response (UR). This type of learning occurs when a previously neutral stimulus is paired with an unconditioned stimulus until it elicits a response similar to that of the unconditioned response.

Related Read: What Is Unconditioned Response (UR)?

Final Thoughts

To the extent that an organism can learn and remember, it must be able to develop expectations about its environment. In other words, it must have some way of evaluating its current situation against experience and predicting what will happen next. The animals also use these predictions to decide whether or not to engage in particular behaviors.

The mechanisms used to evaluate current situations can predict future events. An organism can anticipate events before they occur. A rat that has received an electric shock will avoid entering the room again in the future because it has learned that it leads to pain. The rat may also learn that entering another room leads to food, so that it will go to another place.


  • Prével, A., Rivière, V., Darcheville, J.-C., & Urcelay, G. P. (2016). Conditioned reinforcement and Backward Association. Learning and Motivation, 56, 38–47.
  • Rehman, I., Mahabadi, N., Sanvictores, T., & Rehman, C. I. (2021). Classical Conditioning. In StatPearls. StatPearls Publishing.
  • Andreatta, M., & Pauli, P. (2015). Appetitive vs. aversive conditioning in humans. Frontiers in Behavioral Neuroscience, 9.
  • American Psychological Association. (n.d.). Mystery solved: We now know what happened to little Albert. Monitor on Psychology. Retrieved September 11, 2022, from 

Hi, I am Happy. I'm a professional writer and psychology enthusiast. I love to read and write about human behaviors, the mind, mental health-related topics, and more.