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Unconditioned stimulus in classical conditioning | Examples | Unconditioned stimulus vs neutral stimulus | Unconditioned stimulus vs conditioned stimulus | Little Albert experiment
What is an unconditioned stimulus
In classical conditioning, an unconditioned stimulus (US or UCS) is defined as any stimulus that can naturally and automatically trigger a response without prior learning or practice. It is also called the primary reinforcer. The involuntary response is a reflex triggered whenever the UCS is present.
Unconditioned stimulus in classical conditioning
Russian physiologist, Ivan Pavlov, first discovered classical conditioning when he was feeding his dogs. The dogs would smell the food and automatically salivate. This natural response did not require any prior learning. So the food’s smell was the UCS1. This phenomenon is also called the Pavlovian conditioning.
So, how to find unconditioned stimuli?
A UCS can trigger a response naturally. This response is a biological reaction. A person or animal usually does not have control over this behavior2.
Unconditioned stimulus examples
Here are some examples of the unconditioned stimulus.
- Touching a hot iron Touching a hot iron makes you withdraw your hand right away.
The hot iron is the UCS.
- EatingPutting food into your mouth causes your mouth to water.
The food is the UCS.
- Hurting your footDropping a rock on your foot makes you scream in pain.
The rock is the UCS.
- Inhaling dustDust entering your nose causes you to sneeze.
Dust is the UCS.
The Difference Between Unconditioned Stimulus and Neutral Stimulus
An unconditional stimulus elicits a natural, reflexive response, called the unconditioned response (UCR).
A stimulus that doesn’t naturally elicit a response is a neutral response. For example, food is a UCS for dogs and can cause salivation. But ringing a bell by itself doesn’t trigger the same response. The bell’s sound is hence a neutral stimulus.
The difference between Unconditioned Stimulus and Conditioned Stimulus
A neutral stimulus initially doesn’t trigger any particular response. However, when a neutral stimulus is presented together with a UCS, an association can form.
Classical conditioning happens when a neutral stimulus is paired with an UCS repeatedly to create associative learning. The previously neutral stimulus becomes a conditioned stimulus (CS) and can trigger the same response as the UCS.
So initially, the neutral stimulus does not affect a specific behavior. But after repeatedly presented together with the UCS, it becomes a CS, and the person or animal subconsciously learns to react with the same response when it’s present. This response is then called a conditioned response (CR) or learned response.
For example, in Pavlov’s experiments, he sounded a bell whenever he brought food to his dogs. After multiple repetitions, the dogs learned to expect food and naturally salivated when they heard the bell’s sound even when they did not see the food. When UCS (food) was paired with a previously neutral stimulus (the sound of a bell), the neutral stimulus became a CS.
Little Albert Experiment
Another example of using an unconditioned stimulus to condition a subject is the infamous “Little Albert Experiment.”3
In this experiment, psychologist John B. Watson exposed the infant to a white rat. When the infant attempted to touch the rat, he would make a loud noise to scare him. Several repetitions later, the child cried upon seeing the rat alone.
In this case, the loud noise was an unconditioned stimulus. The rat served as a neutral stimulus, and the child’s cries were unconditioned reflexes.
Psychologists suggest that this type of fear conditioning by an unconditioned aversive stimulus is responsible for psychological disorders such as anxiety disorder and PTSD (Post-Traumatic Stress Disorder)4.
References
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1.
Kimmel HD. Inhibition of the unconditioned response in classical conditioning. Psychological Review. Published online 1966:232-240. doi:10.1037/h0023270
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2.
Clark RE. Classical Conditioning and Brain Systems: The Role of Awareness. Science. Published online April 3, 1998:77-81. doi:10.1126/science.280.5360.77
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3.
Harris B. Whatever happened to little Albert? American Psychologist. Published online 1979:151-160. doi:10.1037/0003-066x.34.2.151
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4.
An unconditioned response is an automatic reflex that occurs in response to an unconditioned stimulus. Unconditioned responses are natural and innate, and therefore, don’t have to be learned. The concept of unconditioned responses was first defined by Ivan Pavlov as part of his discovery of classical conditioning.
- An unconditioned response is a natural and automatic reaction to an unconditioned stimulus; it is present from the time we are born.
- Ivan Pavlov defined unconditioned response as part of the process of classical conditioning, which posits that when a naturally occurring stimulus and an environmental stimulus are repeatedly paired, the environmental stimulus will eventually elicit a similar response to the natural stimulus.
Unconditioned responses are automatic and unlearned. They can be seen from the time we are born. Up until Ivan Pavlov’s experiments that led to the discovery of classical conditioning, however, these innate responses were not yet defined.
Pavlov, a Russian physiologist, set out to study dogs’ digestive systems. However, he noticed something else in the process. While it was natural for a dog to salivate when food was put in its mouth, if the food was paired with something else, like a light turning on or a bell ringing, the animal would soon associate the bell with the food as well. Once a connection between the food and the light or bell was made, even if food wasn’t present, the dog would salivate to the light or the bell by itself.
This process is called classical conditioning. It hinges on pairing an unconditioned stimulus with a neutral stimulus. The neutral stimulus could be anything, but the unconditioned stimulus must provoke a natural, reflexive response. Pairing the unconditional stimulus and neutral stimulus causes the neutral stimulus to become a conditioned stimulus. If these stimuli always occur together, the unconditioned stimulus will become associated with the conditioned stimulus. As a result, the unconditioned response that initially only happened in reaction to the unconditioned stimulus will also occur in response to the conditioned stimulus. The response elicited by the conditioned stimulus is called a conditioned response.
So in the scenario with Pavlov’s dogs, the food is the unconditioned stimulus, salivation is the unconditioned response, the light or bell is the conditioned stimulus, and salivation in response the light or bell is the conditioned response.
Anytime you have an involuntary, unlearned response to a stimulus, it is an unconditioned response. Some examples include:
- Jumping when you hear a loud noise.
- Puckering your mouth when you eat something sour.
- Quickly pulling your hand away from a hot stove.
- Gasping when you get a paper cut.
- Getting goosebumps when you feel cold.
- Jerking your leg when a doctor taps on your knee for a reflex test.
- Feeling hungry when you smell food.
- Blinking when a puff of air is blown in your eye.
- Sneezing when a feather tickles your nose.
- Flinching and perspiring when you receive an electric shock.
- Having your heart rate and breathing slow down when your favorite relative hugs you.
These responses all happen automatically from birth. Any natural reaction is an unconditioned response and in many cases people are not aware of them. Often unconditioned responses are physiological, including salivation, nausea, pupil dilation, and increasing or decreasing heart rate. They also include involuntary motor responses, such as twitching or flinching.
There are key differences between conditioned and unconditioned responses.
- An unconditioned response is innate and natural, it does not have to be learned.
- A conditioned response is learned only when an unconditioned stimulus has become linked in an individual’s mind with a conditioned stimulus.
It’s important to remember that because classical conditioning depends on a set of unconditioned responses, it is restricted to this range of unlearned, automatic responses. For example, suppose that every time you go to a movie theater, the smell of popcorn wafting from the concession stand makes you feel hungry. Over time, if you experience the smell of popcorn with the experience of going to the movie theater enough, you will start to become hungry when you’re walking towards the movie theater or even when you’re making plans to go to the movie theater. In other words, your involuntary, natural response of hunger has become associated with the process of planning and going to a movie theater, even though the experience of going to a movie theater was initially neutral.
Thus, classical conditioning always starts with an unconditioned response to an unconditioned stimulus. And a conditioned response is limited by the range of natural, innate unconditioned responses that we can exhibit.