Ivan Pavlov won the Nobel Prize in 1904 for research on digestion, not learning. While measuring how much his dogs salivated, he noticed something inconvenient: they started salivating before the food arrived, at the sound of footsteps or the sight of the person who fed them. That nuisance became one of the best-known findings in psychology.
Classical conditioning: linking two stimuli
In classical conditioning, you learn that one thing predicts another.
- An unconditioned stimulus (food) triggers an unconditioned response (salivating) with no learning needed.
- A neutral stimulus (a sound) is paired with the food again and again.
- The sound becomes a conditioned stimulus, and salivating at the sound alone is a conditioned response.
The response is involuntary. The dog doesn't decide to salivate.
The story is usually told with a bell. Metronomes and buzzers were the usual signals in Pavlov's lab. His own lectures mention an electric bell, but how often a bell served as the signal is debated.
If the sound keeps coming without food, the response fades: extinction. After a rest, it can briefly return: spontaneous recovery. Similar sounds can trigger it too: generalization.
Operant conditioning: learning from consequences
In 1898 Edward Thorndike put cats in puzzle boxes they could escape by pressing a lever or pulling a loop. Over repeated trials, they escaped faster. He called the principle the law of effect: behavior followed by a satisfying result becomes more likely.
B. F. Skinner built on this from the 1930s and named it operant conditioning, because the animal operates on its environment. In his chambers, rats and pigeons pressed levers or pecked keys for food.
Reinforcement and punishment
Reinforcement makes a behavior more likely. Punishment makes it less likely. "Positive" means something is added and "negative" means something is taken away, not good or bad.
| Add something | Take something away | |
|---|---|---|
| Behavior increases | Positive reinforcement: praise | Negative reinforcement: the seatbelt beep stops |
| Behavior decreases | Positive punishment: a fine | Negative punishment: losing phone time |
Reinforcement schedules
How often a reward comes matters as much as whether it comes.
- Continuous: every response is rewarded. Learning is fast, and extinction is fast too.
- Fixed ratio: a reward after a set number of responses.
- Variable ratio: after an unpredictable number, as with a slot machine. This schedule is the hardest to extinguish.
- Fixed and variable interval: the first response after a set or unpredictable time is rewarded.
Common mix-ups
- Negative reinforcement is not punishment. It increases a behavior, by removing something unpleasant.
- Voluntary or not. Classical conditioning works on automatic responses. Operant conditioning works on voluntary behavior.
- "Positive" doesn't mean nice. A fine is positive punishment because something is added.
Where the research is shaky
The core findings of both kinds of conditioning have been repeated many times, in many species. Some famous examples hold up less well. Watson and Rayner's 1920 "Little Albert" study conditioned fear in a single infant. It had no controls, the fear was never removed, and the child's identity is still disputed. It's a lesson in research ethics more than evidence.
Conditioning also isn't the whole story of learning. Later research showed that animals learn some links more easily than others, and that people learn a lot just by watching.
Frequently asked questions
What is the difference between classical and operant conditioning?
Classical conditioning links two stimuli, so an automatic response moves to a new trigger. Operant conditioning links a voluntary behavior to its consequences.
Is negative reinforcement a punishment?
No. Negative reinforcement removes something unpleasant, and it makes a behavior more likely. Punishment makes a behavior less likely.
Did Pavlov use a bell?
Sometimes. Metronomes and buzzers were the usual signals, and his lectures mention an electric bell, but how often a bell was used is debated.
What is an example of operant conditioning?
A child who gets praise for tidying up tidies more often. That's positive reinforcement.
Try it
Think of a notification sound on your phone. Notice what you feel when you hear it, before you've looked at the screen. That reaction was learned.