In behavioral psychology, an unconditioned stimulus is a type of stimulus that leads to an automatic response. It is the opposite of a conditioned stimulus where the response is learned, rather than automatic.
Unconditioned stimuli, such as tickling, the smell of food, dust in the nose, and freshly chopped onion, lead to natural reactions of our bodies that help protect us from potential dangers.
The concept of an unconditioned stimulus is part of the classical conditioning theory in psychology (a part of the broader behaviorist theory). The ‘father’ of this theory is Ivan Pavlov whose Pavlov’s dog experiment demonstrated conditioned and unconditioned responses in a dog, also known as the Pavlovian response.
Definition of Unconditioned Stimulus
The Russian physiologist Ivan Pavlov has helped us establish a very useful framework for understanding some of the most fundamental characteristics of humans; how people learn.
In Pavlov’s work on the digestive system of dogs, he discovered a principle of learning that he called classical conditioning. In his experiments, he would present a dog with some food and then study the dog’s salivation.
He referred to the food as an unconditioned stimulus (UCS) because it automatically triggered a natural response, which he referred to as an unconditioned response (UCR).
There is no learning that needs to occur for the unconditioned stimulus to trigger the unconditioned response. As we will see below, there are many examples of the stimulus-response connection in our everyday lives.
Examples of Unconditioned Stimulus
1. Tickling (Leads to Giggling)
When someone tickles us, we usually respond with what feels like uncontrollable giggling.
Research has also shown that tickling might even be good for our physical health. It certainly is good for our emotional health.
Using the classical conditioning theory of psychology, the tickling action can be considered the unconditioned stimulus. The object that we use could be a feather or even just our fingertips.
The laughter that it creates is the unconditioned response.
The relationship between the tickle and the laugh is a reflexive one. In fact, not laughing when being tickled is probably impossible.
2. Stubbing Your Toe (Leads to Wincing)
Stimulus: Stubbing a Toe
Response: Wincing and Pain
If you don’t wear shoes inside, then walking around the house can be a bit risky. Nearly everyone has stubbed their toe from time to time. It creates an immediate intense response of pain.
If we examine the anatomy of the foot then we can have a better understanding of what happens. When the toe impacts a hard object, such as a table leg, the sensory neurons in the toe send pain messages up through the spine to an area of the brain in the sensory cortex.
From a classical conditioning framework, the impact is the unconditioned stimulus, and the pain that is felt immediately afterwards is the unconditioned response. There is no learning that needs to happen for your body to have a reaction; it happens automatically.
3. Smell of Food (Leads to Mouth Watering)
Stimulus: Smell of Tasty Food
Response: Mouth Watering
The sight and smell of a delicious meal can elicit a mouth-watering response. There are plenty of examples of this phenomenon, especially during holiday celebrations.
Most countries have celebrations that mark the day their country became independent. This can involve a lot of great food spread about on a long table waiting for ingestion. The display can be a literal smorgasbord of savory sights and smells that will make our mouth water with great anticipation.
This anticipation demonstrates a reflexive association between the sight and smell of food, and the salivatory response that follows. The unconditioned stimulus is the aroma or the image of the food, and the unconditioned response is the salivation that follows.
4. Dust (Leads to Sneezing)
Stimulus: Dust in Nose
Most people think of the immune system as a bunch of T-cells and NK-cells that attack bacteria and viruses once they have entered the body. That is correct. However, the body’s immune system also has a mechanistic component.
For example, when a foreign substance, such as a particle of dust, enters our nose, the immune system activates the sneeze response. Sneezing involves a sudden and somewhat violent expulsion of air through the nostrils. This is done to expel the foreign particle.
Examining the sneeze from a CC perspective, we classify the foreign particle in the nostril as the unconditioned stimulus. This then activates the immune system’s sneeze, which is the unconditioned response.
5. Dicing Onions (Leads to Crying)
Stimulus: Onion Juice
If you hold an onion in your hand and close to your face, nothing will happen. Even though onions are famous for making people cry, this only happens when we are slicing the onion.
When you slice an onion, several chemicals are released into the air. Those chemicals irritate the eye and cause it to water. This is the eye’s natural response to an irritant, and therefore it is called an unconditioned response.
The unconditioned stimulus is comprised of the chemicals that are released into the air. The connection between the unconditioned stimulus and the unconditioned response is so strong that it is automatic.
6. The Sight of Vomit (Leads to Nausea)
Stimulus: Sight of Vomit
Although a bit unpleasant, the sight of vomit is a great example of an unconditioned stimulus. It seems to be a universal trait of people to feel nauseous when seeing another person vomit.
The visual of the puking action creates an almost immediate reaction in people that view it. People will feel sick and may even puke as well. In this case, the sight of the vomit is the unconditioned stimulus, and the reflexive feeling of nausea is the unconditioned response.
From an evolutionary perspective, it is very adaptive that human beings have this UCS – UCR connection. Perhaps the person getting sick has eaten something poisonous. Instead of other people taking too much time trying to understand what has happened, it is much better to have an immediate reaction.
7. Flying Baseball (Leads to Dodging)
Stimulus: Baseball Flying Toward You
Response: Ducking and Dodging to Avoid it
If someone is playing baseball and the ball is hit towards their head, that person will reflexively duck. This is a universal response that will occur for a wide range of objects, not just baseballs.
In fact, it is so automatic, that a person might not have a conscious realization that an object is about to hit them in the face until after they have moved out of the way. This is because the recognition of immediate danger happens much faster than the conscious labelling of the object as “a baseball.”
The object flying towards the face is the unconditioned stimulus and the reflex to duck is the unconditioned response.
8. Alcohol (Leads to Intoxication)
Stimulus: Drinking Alcohol
Drinking alcohol has a consistent effect on people. Once the substance is processed via the digestive system, it makes its way to the brain. At that point, various parts of the brain that are responsible for inhibition are essentially knocked out of commission.
At higher doses of consumption, other areas of the brain may be so affected that a person could have difficulty standing up or walking. Eventually, consumption may be so extreme as to cause a blackout or the loss of consciousness altogether.
The effect of alcohol does not have to be learned. It is universal, consistent, and automatic. Therefore, alcohol qualifies as an unconditioned stimulus.
9. An Infectious Smile (Leads to Smiling)
Stimulus: Person A Smiles
Response: Person B Smiles
Some people just have a great smile. That person usually has a very bubbly and outgoing personality. At first sight of their smile, we instantly feel a tinge of joy and happiness.
Sometimes the infectious smile is called a “contagious smile.” We use those terms because when we see that smile, it makes us want to smile too. In fact, our tendency to smile back may be linked to what are called “mirror neurons” in our brain.
These neurons may be activated when we see that infectious smile, which then makes us smile as well. The infectious smile is a quite pleasant UCS, and a very pleasant one at that.
10. Beautiful Physical Features (Leads to Attraction)
Stimulus: Beautiful physical features
Response: Feelings of attraction
Psychologists and anthropologists have been very interested in identifying the exact physical characteristics that correlate with attractiveness. In males, facial features that are connected to testosterone, such as jaw bone width and a V-shaped torso are considered attractive. In females, wide eyes and prominent cheekbones get high ratings.
These stimuli evoke a natural response in others. Although there are some cross-cultural differences in how attractiveness is defined, there is also a remarkable degree of consistency.
In terms of CC, specific facial features constitute the unconditioned stimulus, and the feeling of being attracted to those features is the unconditioned response.
11. Yawning (Leads to Yawning)
Stimulus: Person A Yawns
Response: Person B Yawns
When someone around us yawns, we seem to have a compulsion to yawn a well. Scientists refer to this phenomenon as ‘social mirroring’. And it doesn’t just happen with yawns. It also happens with leg-crossing and scratching an itch.
According to this study, observing another person yawning increases your likelihood to yawn 6 fold.
Furthermore, this isn’t just a phenomenon in humans. When scientists showed footage of a moues scratching itself to other mice, those other mice also started scratching within 5 seconds.
There are multiple theories about why social mirroring occurs. One compelling one is that, when we observe behavior, we subconsciously see it as potentially beneficial, so we try it out ourselves.
Either way, this action is an example of unconditioned stimulus and response. The yawning reaction isn’t learned – it’s something that we just seem compelled to do.
Related Theoretical Concepts
- Stimulus Discrimination – The ability to tell the difference between various different stimuli and react accordingly
- Stimulus Generalization – The tendency to react to different stimuli in the same manner.
- Response Generalization – The tendency to react to the same stimulus in different ways.
- Conditioned Response – When a response is not natural, but developed when you develop an association between a neutral stimulus and a desired response.
- Higher Order Conditioning – When there are two steps in the conditioning process: the unconditioned stimulus is linked to a conditioned stimulus, which is then linked to another conditioned stimulus. The third stimulus causes an unconditioned response associated with the first stimulus, even if the first and third stimulus are not linked.
The unconditioned stimulus is a very powerful stimulus that will naturally, automatically, and almost immediately trigger an unconditioned response. We can see the power of the unconditioned stimulus is our everyday lives and in a wide range of situations.
For example, tickling will generate laughter, while the sight of vomit will make us nauseous. Slicing and dicing a fresh onion will bring tears to our eyes, while a little dust in the nose will make us sneeze. Too much alcohol will make us walk funny and stub our toe, which will make us feel pain.
The unconditioned stimulus – response connection is vital to our health and plays an important role in our interactions and relations with others.
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