Psicologia

Classical conditioning (Pavlov): summary with diagram and 5 solved exercises

What classical conditioning is: unconditioned stimulus, conditioned stimulus, acquisition, extinction, generalization and discrimination, explained through Pavlov's model, with 5 solved exercises and 3 FAQs.

Recommended for: Grade 11 · Grade 12

Classical conditioning is the form of learning in which a previously meaningless stimulus, repeatedly paired with a stimulus that already triggers an automatic reaction, ends up triggering that reaction by itself. It is what happens to Ivan Pavlov’s dogs, which start salivating at the sound announcing food, before they even see it.

The four labels not to confuse

The whole model rests on four elements. The unconditioned stimulus (US) produces a reaction with no learning involved: food in the mouth. The reaction that follows is the unconditioned response (UR): salivation. Any stimulus that does not produce that reaction at first is the neutral stimulus (NS): a sound, a light, a metronome.

When the neutral stimulus is presented several times shortly before the unconditioned stimulus, it changes function and becomes the conditioned stimulus (CS). The reaction it now produces on its own is the conditioned response (CR). UR and CR look alike, but they are not the same thing: the first is innate, the second is learned and usually weaker.

Pavlov’s experiment

Pavlov studied the physiology of digestion and measured his dogs’ saliva through a fistula. He noticed something he was not looking for: the animals already salivated when the attendant carrying the food arrived. He called it “psychic secretion” and decided to study it systematically, pairing a sound with the delivery of meat. After a few repetitions the sound alone was enough.

Order and timing matter. Conditioning works well when the conditioned stimulus precedes the unconditioned one by a short interval, because it has to work as a signal that announces. If it follows, learning is weak or absent.

Acquisition, extinction, spontaneous recovery

The phase in which the conditioned response forms and strengthens is acquisition. If the conditioned stimulus is then presented many times without the unconditioned one, the response weakens until it disappears: this is extinction.

Disappeared, however, does not mean erased. After a rest period, the conditioned stimulus alone reactivates the response, weaker but present: this is spontaneous recovery. And if the two stimuli are paired again, reacquisition is far quicker than the original learning. These are the signs that the original association was still there underneath.

Generalization and discrimination

A dog conditioned to a 1000 Hz tone also responds to 900 and 1100 Hz, and the further the tone moves from the original, the weaker the response: this is stimulus generalization, and the resulting curve is the generalization gradient.

The opposite process comes from training: if only one tone is always followed by food and the others never are, the dog learns to respond to that one only. This is discrimination, a selective extinction applied to every similar stimulus except one.

Higher-order conditioning

A well-established conditioned stimulus can itself become the basis for new learning: if a light is repeatedly paired with the sound that already announces food, the light too starts producing salivation, even though it was never accompanied by food. This is higher-order conditioning, and it explains why a fear or a preference spreads in a chain to situations further and further from the original episode.

Where you find it outside the lab

Pavlov’s model explains many ordinary things: the anxiety rising in a dentist’s waiting room, the lasting disgust for a food eaten before an episode of sickness (the taste aversion studied by Garcia, which forms after a single pairing and even hours later), phobias, and the way advertising places a neutral product next to images that already produce positive emotions.

In the exercises below you will find the same model applied in increasing order of difficulty: first recognizing the labels in an everyday scene, then reasoning about extinction and spontaneous recovery, reading a generalization gradient from numerical data, and finally analysing how a phobia forms and why avoidance keeps it alive.

Solved exercises

1. Luke's oven beeps when cooking is over, and every time a tray of warm cookies comes out right afterwards. After a few weeks Luke's mouth waters as soon as he hears the beep, even when the oven contains a lasagna. Identify the unconditioned stimulus, unconditioned response, neutral stimulus, conditioned stimulus and conditioned response. base

Show solution
  1. First I look for the reaction that already exists without any learning: salivating in front of food. So the unconditioned stimulus (US) is the smell and taste of the cookies.
  2. The reaction that stimulus triggers automatically is the unconditioned response (UR): salivating at the cookies.
  3. Then I look for the stimulus that triggered nothing at the start: the oven beep. Before learning, it is the neutral stimulus (NS).
  4. The beep is presented repeatedly shortly before the cookies: the pairing turns it into a conditioned stimulus (CS).
  5. The salivation that now appears at the beep alone, with no cookies, is the conditioned response (CR).
  6. Consistency check: UR and CR are the same physiological reaction but have different causes. The UR is innate, the CR is learned.

Answer: US = smell and taste of the cookies; UR = salivating at the cookies; NS = the beep before learning; CS = the beep after the pairings; CR = salivating at the beep alone

2. True or false? Correct the false statements. a) For classical conditioning to occur, the subject must do something to earn a reward. b) Pavlov won the Nobel Prize for discovering conditioning. c) If the neutral stimulus is presented after the unconditioned stimulus, conditioning is faster. d) The conditioned response is usually weaker than the unconditioned response. base

Show solution
  1. a) False. That describes Skinner's operant conditioning, where the behaviour is voluntary and is shaped by its consequences. In classical conditioning the subject is passive and the response is reflexive.
  2. b) False. Pavlov received the 1904 Nobel Prize in Physiology or Medicine for his work on digestion. Conditioning emerged as an unplanned side finding of that research: the dogs salivated before receiving any food.
  3. c) False. The opposite order works. Conditioning is effective when the neutral stimulus shortly precedes the unconditioned one (delayed conditioning, typically fractions of a second to a few seconds): the signal must announce the event, not follow it.
  4. d) True. The conditioned response is typically weaker and slower: Pavlov's dogs salivated less to the sound than to the meat itself.

Answer: a) False (that is operant conditioning); b) False (1904 Nobel for the physiology of digestion); c) False (the neutral stimulus must precede the unconditioned one); d) True

3. An office coffee machine hums for a few seconds before pouring. Mark's mouth now waters at the hum. For one week the machine breaks down: it hums but pours nothing, and after about twenty trials Mark's reaction disappears. Mark then takes a two-week holiday; back at work he hears the hum and the reaction returns, though weaker. Name the three phases and explain what the last one proves. intermedio

Show solution
  1. Phase one: the hum (NS) regularly precedes the coffee (US) and becomes a CS. This is acquisition.
  2. Phase two: the hum is presented without the coffee. The pairing breaks and the conditioned response fades until it disappears. This is extinction.
  3. Phase three: after a rest period with no stimuli, the hum alone reactivates the response. This is spontaneous recovery.
  4. I interpret spontaneous recovery: if extinction had erased the learning, nothing would be left to recover after the break.
  5. Since the response does come back, extinction does not delete the original link but layers a new inhibitory learning on top of it, and that inhibition weakens over time.
  6. Check: the recovered response is weaker than the original one, which fits an original association that is still present but partly inhibited.

Answer: Acquisition, extinction and spontaneous recovery. Spontaneous recovery shows that extinction does not erase the learned association but inhibits it through additional learning.

4. A dog was conditioned with a 1000 Hz tone and produces 60 drops of saliva when the conditioned stimulus is presented. Tested with other tones and no food it produces: 800 Hz → 45 drops; 900 Hz → 54; 1000 Hz → 60; 1100 Hz → 51; 1200 Hz → 39. Express each response as a percentage of the conditioned stimulus, name the pattern you obtain, and explain how you would make the dog respond only to 1000 Hz. intermedio

Show solution
  1. I take the response to the conditioned stimulus as 100 per cent: 60 drops at 1000 Hz.
  2. 800 Hz: 45 / 60 = 0.75, that is 75 per cent.
  3. 900 Hz: 54 / 60 = 0.90, that is 90 per cent.
  4. 1000 Hz: 60 / 60 = 1.00, that is 100 per cent.
  5. 1100 Hz: 51 / 60 = 0.85, that is 85 per cent.
  6. 1200 Hz: 39 / 60 = 0.65, that is 65 per cent.
  7. Reading the numbers: the response peaks on the conditioned stimulus and drops as the tone moves away from it. This is stimulus generalization, and the curve is called the generalization gradient.
  8. To get a response only at 1000 Hz you need discrimination training: keep pairing 1000 Hz with food and always present the other tones without food, so that only those extinguish.

Answer: 75 per cent at 800 Hz, 90 per cent at 900 Hz, 100 per cent at 1000 Hz, 85 per cent at 1100 Hz, 65 per cent at 1200 Hz. The pattern is the generalization gradient; responding only to 1000 Hz requires discrimination training, reinforcing that tone alone and extinguishing the others.

5. Sara is trapped in a stuck lift for twenty minutes and has a panic attack. Since then she fears lifts, then also the lobby where the lift is, and finally she avoids that building altogether. Explain how the phobia forms in terms of classical conditioning, name the mechanism behind the fear of the lobby, explain why avoidance stops the fear from fading, and state the principle exposure therapy relies on. avanzato

Show solution
  1. I reconstruct the first episode: being trapped is the unconditioned stimulus, panic is the unconditioned response. The lift, previously neutral, becomes a conditioned stimulus and now produces fear on its own, the conditioned response.
  2. A single pairing was enough because the unconditioned stimulus was very intense: with strongly emotional events, one-trial learning is common.
  3. The fear of the lobby does not come from a second entrapment. The lobby becomes associated with the lift, which is already a conditioned stimulus: this is higher-order conditioning, where a conditioned stimulus acts as an unconditioned stimulus for a new one.
  4. Extending the fear to the whole building is generalization instead: stimuli similar to the original context evoke the same response.
  5. For the fear to fade, extinction would be needed: meeting the lift without anything bad happening. By avoiding it, Sara never has that experience, so the association stays intact and is never disconfirmed.
  6. On top of that, avoidance immediately reduces anxiety, so it is negatively reinforced: an operant loop that protects the underlying classical association.
  7. Conclusion: exposure therapy, and Wolpe's systematic desensitization, do exactly what avoidance prevents. They present the conditioned stimulus gradually without the unconditioned stimulus, and pair it with an incompatible response such as relaxation (counterconditioning).

Answer: Being trapped = US, panic = UR, the lift = CS, fear of the lift = CR. Fear of the lobby is higher-order conditioning; extending it to the whole building is generalization. Avoidance blocks extinction because it removes the experiences that would disconfirm the association, and it is maintained by immediate relief. Exposure therapy is based precisely on extinction, combined with counterconditioning.

FAQ

What is the difference between classical and operant conditioning?

Classical conditioning associates two stimuli, and the response is an involuntary reflex that comes before any consequence: the subject need not do anything. Operant conditioning associates a voluntary behaviour with its consequence, which makes that behaviour more or less likely. Salivating at a sound is classical; pressing a lever to get food is operant.

Does extinction really erase what was learned?

No. If the conditioned stimulus is presented long enough without the unconditioned one the response disappears, but three findings show the association survives: spontaneous recovery after a break, much faster reacquisition than the original learning, and the return of the response when the context changes. Extinction is therefore extra learning that inhibits the first, not a deletion.

What was the Little Albert experiment and why is it still studied?

In 1920 Watson and Rayner conditioned a boy of about eleven months to fear a white rat by pairing it with a loud noise behind his head, and the fear generalized to other furry objects. It is still studied because it shows that human emotions can be conditioned, and because it is a textbook case of research that would be unacceptable today: no informed consent and no deconditioning procedure.