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Classical
Conditioning

Discover how associations between stimuli shape behavior: from Pavlov's dogs to everyday learning.

AP Psychology

What is Classical Conditioning?

Classical conditioning is a type of associative learning in which an organism learns to link two stimuli together. A previously neutral stimulus comes to trigger a response after being paired with a stimulus that naturally triggers that response.

Key Terminology

US
Unconditioned Stimulus: Naturally triggers a response without learning (e.g., food)
UR
Unconditioned Response: Automatic reaction to the US (e.g., salivation to food)
NS
Neutral Stimulus: Initially produces no relevant response (e.g., a bell before conditioning)
CS
Conditioned Stimulus: The former NS that now triggers a response after pairing (e.g., the bell after conditioning)

The Conditioned Response

The Conditioned Response (CR) is the learned reaction to the conditioned stimulus. It is typically similar to the UR but is triggered by the CS instead of the US.

The Conditioning Process

Before Conditioning Food (US) Salivation (UR) Bell (NS) No Response During Conditioning Bell (NS) + Food (US) Salivation (UR) After Conditioning Bell (CS) CR Repeated Pairings
\( \text{NS} + \text{US} \to \text{UR} \)
After learning:
\( \text{CS} \to \text{CR} \)

Acquisition and Timing

Acquisition is the initial learning phase when the NS and US are repeatedly paired. The strength of the CR depends on the timing and consistency of pairings.

Delay Conditioning
CS begins before the US and overlaps with it. Most effective method for producing strong conditioning.
Trace Conditioning
CS starts and ends before the US begins. Works, but requires the brain to hold a memory trace.
Backward Conditioning
US comes before the CS. Produces weak or no conditioning because the CS cannot predict the US.

Key Phenomena in Classical Conditioning

1
Extinction: When the CS is repeatedly presented without the US, the CR gradually weakens and disappears.
2
Spontaneous Recovery: After extinction, the CR can reappear following a rest period when the CS is presented again.
3
Generalization: The tendency to respond to stimuli similar to the CS (e.g., different bell tones also trigger salivation).
4
Discrimination: The learned ability to distinguish between the CS and other similar stimuli that do not signal the US.

Generalization vs. Discrimination

Response Strength Stimulus Similarity to CS Generalization Gradient CS Less Similar Less Similar Discrimination = Steeper gradient

Higher-Order Conditioning

In higher-order (second-order) conditioning, a new neutral stimulus is paired with an already established CS rather than directly with the US. The new stimulus can then also elicit a CR.

Step 1: Standard Conditioning Bell (CS) Salivation (CR) Step 2: Higher-Order Light (NS2) + Bell (CS1) Result Light (CS2) CR

How to Identify Classical Conditioning

1
Find the automatic response. Look for a reflexive or involuntary reaction (fear, salivation, nausea, startle). This is the UR.
2
Identify what naturally causes it. What stimulus automatically triggers the UR without learning? This is the US.
3
Find the new trigger. What neutral stimulus was paired with the US? After learning, this becomes the CS.
4
Name the learned response. The response to the CS is the CR. It usually resembles the UR but is triggered by the CS.
5
Verify involuntariness. Classical conditioning involves involuntary responses. If the behavior is voluntary/chosen, it is likely operant conditioning instead.

Example 1: Pavlov's Dogs

Pavlov repeatedly rang a bell just before presenting food to his dogs. After many pairings, the dogs began to salivate at the sound of the bell alone.

US
Food (meat powder)
UR
Salivation to food
CS
Bell (after pairing)
CR
Salivation to bell

Example 2: Little Albert

Watson and Rayner (1920) presented 9-month-old Albert with a white rat (NS) paired with a loud, startling noise (US). After several pairings, Albert showed fear at the sight of the rat alone.

US
Loud noise (hammer on steel bar)
UR
Fear/crying to loud noise
CS
White rat (after pairing)
CR
Fear/crying at sight of rat

Example 3: Taste Aversion

After eating sushi at a restaurant and then getting sick from the flu, you feel nauseous the next time you smell sushi, even though the flu caused the illness, not the food.

US
Flu virus (caused illness)
UR
Nausea from the flu
CS
Sushi (taste/smell)
CR
Nausea at smell of sushi

Common Mistakes

✕ Confusing CS and US
The US naturally triggers a response with no learning required. The CS only triggers a response after being paired with the US. Always ask: "Did this need to be learned?"
✕ Confusing UR and CR
The UR and CR often look identical (both are salivation), but they differ in their trigger. UR is to the US; CR is to the CS.
✕ Mixing Up Classical and Operant
Classical conditioning involves involuntary, reflexive responses. If the organism is choosing a behavior for a reward/punishment, it is operant conditioning.

Classical vs. Operant Conditioning

Classical Operant
Type of Behavior Involuntary / Reflexive Voluntary / Chosen
Key Mechanism Association between stimuli Consequences of behavior
Response Timing Before the behavior (CS predicts US) After the behavior (reward/punishment)
Founder Ivan Pavlov B.F. Skinner
Example Dog salivates to bell Rat presses lever for food
Extinction CS presented without US Behavior no longer reinforced

Question 1 of 5

A child is bitten by a dog and subsequently becomes afraid of all dogs. In this example, what is the conditioned stimulus (CS)?

Question 2 of 5

After conditioning, a dog salivates to a 1000 Hz tone (CS). It also salivates, but less, to an 800 Hz tone. This best demonstrates:

Question 3 of 5

A researcher conditions a rat to fear a light by pairing it with a shock. Then the researcher repeatedly presents the light without the shock. After many trials, the rat no longer fears the light. Weeks later, the rat again shows a fear response to the light. This is an example of:

Question 4 of 5

Which of the following scenarios is the best example of classical conditioning rather than operant conditioning?

Question 5 of 5

Garcia and Koelling's research on taste aversion demonstrated that classical conditioning: