In classical conditioning, a conditioned stimulus is an initially neutral stimulus that eventually triggers a response after being repeatedly paired with an unconditioned stimulus. For example, after Ivan Pavlov repeatedly paired a tone with meat powder, the tone became a conditioned stimulus because it began to independently elicit salivation from the dogs.

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Classical conditioning is a type of associative learning in which organisms learn to connect events that repeatedly happen together. Through this process, a reflexive response originally elicited by one stimulus can be mapped to a different stimulus by training an association between the two.

Classical Conditioning

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

1) Pavlov presented his  dogs with the sound of a bell (NS) which did not elicit any response


2) Started to pair the sound of the bell (NS) with food (US), which did elicit an unconditioned response (salivation)


3) After repeated presentation, the sound of the bell alone (now the CS) made the dogs salivate (CR) 

(McLeod 2018)

Ivan Pavlov's dogs

Extinction is the process in classical conditioning where a learned response diminishes and eventually vanishes. This occurs when the conditioned stimulus (CS) is repeatedly presented without the unconditioned stimulus (UCS). As the association between the two stimuli weakens, the organism's conditioned response (CR) becomes progressively weaker until it ceases entirely. For instance, Pavlov observed this when he repeatedly sounded a tone for his dogs without providing meat powder, which led to the dogs eventually stopping their salivation response to the tone.

Extinction

Acquisition is the initial learning phase in classical conditioning where a neutral stimulus is repeatedly paired with an unconditioned stimulus. With each pairing, the strength of the conditioned response increases. This process of repeated association gradually transforms the neutral stimulus into a conditioned stimulus, which can then elicit the conditioned response on its own.

Acquisition

Can a behavior be conditioned if the neutral stimulus is presented after the unconditioned stimulus?

Spontaneous recovery is the re-emergence of a conditioned response that had previously been extinguished. This phenomenon occurs after a rest period during which the conditioned stimulus is not presented. For example, Pavlov observed that after his dogs underwent extinction training and stopped salivating to a bell, they would once again begin to salivate at the sound of the bell following a few hours of rest.

Spontaneous Recovery

- Unconditioned stimulus (US): stimulus that produces an automatic response without prior conditioning


- Unconditioned response (UR): unconditioned reaction automatically elicited by the unconditioned stimulus


- Neutral stimulus (NS): a stimulus that elicits no response before conditioning


- Conditioned stimulus (CS): a previous NS that elicits a conditioned response after being paired with the US


- Conditioned response (CR): the learned response to the conditioned stimulus after the CS and US are paired


(Spielman 2020)

Classical Conditioning: Terms

An example of classical conditioning can be seen during a thunderstorm. A person naturally jumps (a reflex) in response to a loud boom of thunder. If a flash of lightning consistently precedes the thunder, the person may learn to associate the two stimuli. Consequently, they may begin to jump at the sight of lightning alone, in anticipation of the thunder.

Classical Conditioning: Lightning and Thunder

A real-world example of classical conditioning can be seen in cancer patients undergoing chemotherapy. For instance, a patient named Moisha vomited after her treatments. The chemotherapy drugs were the unconditioned stimulus (UCS) that caused the unconditioned response (UCR) of vomiting. After repeated visits, the doctor's office, which was previously neutral, became a conditioned stimulus (CS). Consequently, Moisha began to feel nauseous—the conditioned response (CR)—simply upon visiting the oncologist's office, even before receiving treatment.

Classical Conditioning in Chemotherapy Patients

A common example of classical conditioning involves a cat named Tiger. The cat's food serves as the unconditioned stimulus (UCS), which naturally elicits excitement as the unconditioned response (UCR). A specific electric can opener, used only for the cat's food, makes a distinct sound. This sound, initially a neutral stimulus, becomes a conditioned stimulus (CS) after being repeatedly paired with the food. Consequently, Tiger learns to get excited and run to the food preparation area—the conditioned response (CR)—upon hearing the sound of the can opener alone.

Classical Conditioning in a Cat

At Stingray City in the Cayman Islands, southern stingrays provide a real-world example of classical conditioning. The process began when fishermen regularly cleaned fish and conch (unconditioned stimulus) at a sandbar, causing stingrays to gather to eat (unconditioned response). Over the years, the stingrays learned to associate the sound of boat engines, initially a neutral stimulus, with this food source. As a result, the engine noise became a conditioned stimulus, prompting a conditioned response where dozens of stingrays now swarm tour boats, bumping and rubbing against people in anticipation of being fed treats like squid. This response is maintained by the presence of food, as the stingrays leave once the treats are gone.

Classical Conditioning in Stingrays

An example of classical conditioning in infants involves a six-month-old named Angelina and her baby formula. The formula is an unconditioned stimulus (UCS) that naturally elicits excitement and salivation as an unconditioned response (UCR). Initially, the blue canister containing the formula is a neutral stimulus. Through repeated association with the formula, Angelina learns that the canister signals feeding time. Consequently, the canister becomes a conditioned stimulus (CS), and the sight of it alone is enough to trigger a conditioned response (CR), such as excitement and reaching for the container.

Classical Conditioning in an Infant with a Formula Canister

Classical conditioning is not limited to food-related stimuli and can be used to condition emotional responses like fear. For instance, in the case of an invisible electric dog fence, a dog learns to associate the edge of the yard (a neutral stimulus) with the discomfort of a small electrical shock (an unconditioned stimulus). After this pairing, the edge of the yard becomes a conditioned stimulus that elicits fear and anxiety (the conditioned response), compelling the dog to stay within the designated boundaries.

Classical Conditioning with an Electric Dog Fence

A humorous example of classical conditioning is depicted in the television show *The Office*. In the scene, a character named Jim conditions his coworker, Dwight, by repeatedly making a specific computer sound before offering him a breath mint. After several pairings, the sound alone, which was initially a neutral stimulus, becomes a conditioned stimulus, causing Dwight to automatically expect a mint, demonstrating a conditioned response.

Classical Conditioning in 'The Office'

Robert Rescorla was a prominent researcher who, along with his colleague Allan Wagner, significantly advanced the understanding of classical conditioning. He demonstrated that the predictive power of a conditioned stimulus (CS) over the occurrence of an unconditioned stimulus (UCS) is a critical factor in the learning process. Their work culminated in the development of the Rescorla-Wagner model.

Robert Rescorla

In classical conditioning, a neutral stimulus (NS) is a stimulus that does not naturally elicit a response prior to conditioning. During the conditioning process, it is presented immediately before an unconditioned stimulus.

Neutral Stimulus

A classic example of classical conditioning involves a dog, food, and a bell. Before conditioning, the dog naturally salivates to food but not to a ringing bell. During conditioning, the bell is rung whenever food is presented. After conditioning, the dog learns to associate the bell with the food and begins salivating to the bell alone.

Pavlov's Dog Experiment

Classical conditioning frequently occurs in real-world medical situations, such as cancer chemotherapy. Chemotherapy drugs act as an unconditioned stimulus that naturally produces vomiting, the unconditioned response. Through repeated pairings, the doctor's office becomes a conditioned stimulus. Consequently, visiting the office alone can trigger a conditioned response of nausea.

Classical Conditioning of Nausea in Cancer Patients

Higher-order conditioning, or second-order conditioning, occurs when an established conditioned stimulus is paired with a new neutral stimulus, causing the new stimulus to also elicit the conditioned response. For example, if a doctor's office is already a conditioned stimulus that triggers nausea, learning to associate a syringe with the doctor's office can cause the syringe alone to produce nausea, even if it was never directly paired with the original unconditioned stimulus.

Higher-Order Conditioning

An example of classical conditioning occurs when a cat repeatedly hears the sound of an electric can opener before being fed. Over time, the cat associates the sound with receiving food, causing it to become excited and run to the feeding area whenever it hears the can opener alone.

Classical Conditioning Cat Example

The southern stingrays at Stingray City provide a real-world example of classical conditioning. Over time, these normally solitary animals became accustomed to interacting with humans and learned to associate the sound of a boat engine with food. Much like Pavlov's dogs, the stingrays learned that a neutral stimulus (boat engine sound) predicted an unconditioned stimulus (food), eventually leading to a conditioned response.

Stingray City Classical Conditioning Example

Taste aversion is an evolutionary adaptation designed to help organisms quickly learn to avoid harmful foods. This form of conditioning is unique because it can occur based on a single instance and involve an extended time lapse between the event (consuming the food) and the negative stimulus (illness). This rapid learning contributes to species survival via natural selection by helping organisms avoid stimuli that pose real dangers to their health and welfare.

Evolutionary Adaptation of Taste Aversion

In classical conditioning, extinction is the decrease in the conditioned response when the unconditioned stimulus is no longer presented with the conditioned stimulus. Over time, as the conditioned stimulus is repeatedly presented alone, the organism's response gradually weakens and eventually disappears.

Extinction (Classical Conditioning)

A chart illustrates the four main stages of classical conditioning over time. The x-axis represents time, and the y-axis represents the strength of the Conditioned Response (CR). The four columns of graphed data represent Acquisition, Extinction, a Pause, and Spontaneous Recovery followed by further Extinction.

Classical Conditioning Stages Graph

In 1920, John B. Watson and Rosalie Rayner conducted an experiment with a baby nicknamed Little Albert. They demonstrated that fears can be conditioned by exposing Little Albert to a neutral white rat and repeatedly pairing it with a sudden, loud noise. The loud noise naturally caused a reflexive fear response. Eventually, Little Albert became frightened by the white rat alone, showing that emotions could become conditioned responses.

Little Albert Experiment

Ivan Pavlov's experiments demonstrated that classical conditioning is the process through which stimulus-response bonds are formed. This occurs when an organism learns to associate two events that repeatedly happen together, causing a reflexive response to one stimulus to become associated with a different, previously neutral stimulus.

Stimulus-Response Bonds in Classical Conditioning

An experiment with rabbits illustrates the cerebellum's role in classical conditioning. Researchers conditioned the animals to blink upon receiving a puff of air to their eyes. After sustaining damage to their cerebellums, the rabbits lost the ability to learn this conditioned eye-blink response, demonstrating the cerebellum's necessity for this type of implicit memory formation.

Example of Cerebellum's Role in Classical Conditioning: Rabbit Eye-Blink Experiment

Classical conditioning involves three distinct phases. Before conditioning, an unconditioned stimulus produces an unconditioned response, and a neutral stimulus produces no response. During conditioning, the unconditioned stimulus is presented repeatedly just after the neutral stimulus. After conditioning, the neutral stimulus alone produces a conditioned response.

Classical Conditioning Phases

A real-world example of classical conditioning can be seen in cancer patients undergoing chemotherapy. The chemotherapy drugs serve as the unconditioned stimulus (UCS) that naturally causes vomiting, the unconditioned response (UCR). After repeated pairings, the doctor's office becomes a conditioned stimulus (CS), which elicits nausea, the conditioned response (CR), even before the drugs are administered.

Classical Conditioning in Chemotherapy

Consider an example of classical conditioning where a cat named Tiger is fed using a special electric can opener. For every meal, Tiger hears the distinctive sound of the electric can opener ("zzhzhz") and then gets her food. Tiger quickly learns that when she hears "zzhzhz" she is about to get fed. As a result, she gets excited and runs to where the food is being prepared. In this case, what are the unconditioned stimulus (UCS), conditioned stimulus (CS), unconditioned response (UCR), and conditioned response (CR)?

Classical Conditioning Example: Cat and Can Opener

At Stingray City in the Cayman Islands, southern stingrays provide a real-world example of classical conditioning. These stingrays have been classically conditioned to associate the sound of a boat motor with food provided by tourists.

Classical Conditioning of Stingrays

Organisms learn to predict the occurrence of an unconditioned stimulus (UCS) from a conditioned stimulus (CS). Robert Rescorla demonstrated that classical conditioning involves this predictive relationship, where the CS reliably signals that the UCS is coming.

Prediction in Classical Conditioning

Classical conditioning processes, which include acquisition, extinction, and spontaneous recovery, apply in humans to connect neutral stimuli with unconditioned stimuli.

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