Unit 4 · Learning Theory · Reading 2 of 13
Pavlov's Dogs: The Five Parts
Before you read
Most people "know" Pavlov rang a bell. He mostly didn't. Watch for what he actually used, because that detail separates people who read this from people who didn't.
Words you'll own by the end
- Neutral stimulus (NS): causes no particular response before learning.
- Unconditioned stimulus (UCS): triggers a response automatically, with no learning.
- Unconditioned response (UCR): the automatic, unlearned reaction to the UCS.
- Conditioned stimulus (CS): the old neutral stimulus, now learned. It triggers a response by itself.
- Conditioned response (CR): the learned reaction to the CS.
1. A digestion scientist notices something odd
Ivan Pavlov wasn't a psychologist. He studied the physiology of digestion in dogs and won a Nobel Prize for it in 1904. While running those studies, he noticed that his dogs started to salivate when they heard the footsteps of the people who fed them.
Drooling at food makes sense; nobody teaches a dog that. Drooling at footsteps doesn't. The dogs must have learned that footsteps meant food was coming. That observation started one of the most famous studies in psychology.
2. The experiment
Pavlov paired two things:
- Meat powder, which makes any dog salivate automatically.
- The sound of a metronome (a ticking device musicians use to keep time), which at first caused no reaction at all.
He played the metronome and then immediately gave the meat powder. After many repeated pairings, the dogs salivated at the sound of the metronome alone, with no food in sight.
Timing mattered. If the sound and the food came close together, the dogs learned the link quickly. If there was a long gap, the learning was weaker and slower.
Check-in: What did Pavlov actually use to signal the food in his famous studies?
3. The five parts
Every classical conditioning example has the same five parts. For each one, there's a question to ask yourself.
Pavlov's experiment in three stages
Before conditioning
Food works on its own. The metronome does nothing yet.
During conditioning (repeated pairings)
Sound first, food right after, over and over. The dog is building the link.
After conditioning
The sound works alone. The metronome's label changed from NS to CS, and the drool's label changed from UCR to CR.
Neutral stimulus (NS): causes no particular response before conditioning. It's the thing that will become the CS.
Ask: What didn't matter at first?
Unconditioned stimulus (UCS): the thing the learner reacts to automatically. Start here when you break down any example.
Ask: What caused a reaction without any learning?
Unconditioned response (UCR): the natural, unlearned reaction to the UCS.
Ask: What did the learner do automatically?
Conditioned stimulus (CS): the old NS, after repeated pairings with the UCS.
Ask: What is the learner now reacting to that they didn't react to before?
Conditioned response (CR): the new, learned reaction to the CS.
Ask: What reaction did the learner learn?
The trap most students fall into
In Pavlov's study, the UCR and the CR are the same behavior: salivation. What makes them different is what triggers it. Drool caused by food is the UCR. Drool caused by the metronome is the CR. Always ask, "a response to what?"
Check-in: After conditioning, what is the metronome called?
4. Same five parts, new example
When you come home, your new puppy hears your keys rattle just before the door opens. At first the keys mean nothing to him. But he's thrilled every time he sees you, and now his heart starts racing as soon as he hears the keys.
- UCS: seeing you come home (exciting with no learning needed)
- UCR: heart racing when he sees you
- NS → CS: the sound of the keys
- CR: heart racing at the sound of the keys
Why the keys and not the TV or a squeaky toy? Because the keys reliably come right before you walk in. You'll learn the name for that idea in Reading 3.
Try it: Label a new example
During a storm, you see a flash of lightning, and a second later a crack of thunder makes you jump. After a few storms, you flinch at the flash alone, before any thunder.
Am I ready for a pop quiz?
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