What is the stimulus called which elicits an unconditioned response when presented with unconditioned stimulus?

In classical conditioning, an unconditioned response is an unlearned response that occurs naturally in reaction to the unconditioned stimulus. For example, if the smell of food is the unconditioned stimulus, the feeling of hunger in response to the smell of food is the unconditioned response.

Examples of Unconditioned Responses

Have you ever accidentally touched a hot pan and jerked your hand back in response? That immediate, unlearned reaction is a great example of an unconditioned response. It occurs without any type of learning or training.

Some more examples of unconditioned responses include:

• Gasping in pain after being stung by a bee
• Jerking your hand back after touching a hot plate on the oven
• Jumping at the sound of a loud noise
• Twitching your leg in response to a doctor tapping on your knee
• Salivating in response to a sour taste
• Jumping back from a growling dog

In each of the above examples, the unconditioned response occurs naturally and automatically.

The Unconditioned Response and Classical Conditioning

The concept of the unconditioned response was first discovered by a Russian physiologist named Ivan Pavlov. During his research on the digestive systems of dogs, the animals in his experiment would begin to salivate whenever they were fed. Pavlov noted that when a buzzer was rung every time the dogs were fed, the animals eventually began to salivate in response to the buzzer alone.

In Pavlov's classic experiment, the food represents what is known as the unconditioned stimulus (UCS). The UCS naturally and automatically triggers a response. Pavlov's dogs salivating in response to the food is an example of the unconditioned response.

By repeatedly pairing a conditioned stimulus (the sound of the buzzer) with the unconditioned stimulus (the food), the animals eventually came to associate the sound of the buzzer with the presentation of food. At this point, salivating in response to the sound of the buzzer became the conditioned response.

Unconditioned Response and Conditioned Response Differences

When trying to distinguish between the unconditioned response and the conditioned response, try to keep a few key things in mind:

• The unconditioned response is natural and automatic
• The unconditioned response is innate and requires no prior learning
• The conditioned response will occur only after an association has been made between the UCS and the CS
• The conditioned response is a learned response

For example, you naturally tend to tear up whenever you are cutting onions. As you are making dinner, you also enjoy listening to music and find yourself playing the same song quite often. Eventually, you find that when you hear the song you often play during your meal prep, you find yourself tearing up unexpectedly. In this example, the vapors from the onions represent the unconditioned stimulus. They automatically and naturally trigger the crying response, which is the unconditioned response.

After multiple associations between a certain song and the unconditioned stimulus, the song itself eventually starts to evoke tears.

So what happens when an unconditioned stimulus is no longer paired with a conditioned stimulus? When the conditioned stimulus is presented alone without the unconditioned stimulus, the conditioned response will eventually diminish or disappear, a phenomenon known as extinction.

In Pavlov's experiment, for example, ringing the buzzer without presenting food eventually led the dogs to stop salivating in response to the buzzer. Pavlov found, however, that extinction does not lead to the subject returning to their previously unconditioned state. In some cases, allowing a period of time to elapse before suddenly reintroducing the conditioned stimulus can lead to spontaneous recovery of the response.

You should read more about how this process as well as some of the key differences between how classical and operant conditioning work.

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1. Eelen P. Classical conditioning: Classical yet modern. Psychol Belg. 2018;58(1):196–211. doi:10.5334/pb.451

2. Dunsmoor JE, Niv Y, Daw N, Phelps EA. Rethinking extinction. Neuron. 2015;88(1):47–63. doi:10.1016/j.neuron.2015.09.028

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