Processes in Classical Conditioning: Learn It 1—Acquisition and Extinction

  • Describe the processes of acquisition, extinction, and spontaneous recovery
  • Describe the processes of generalization and discrimination

Now that you’ve seen how classical conditioning works, let’s examine how learned associations form, weaken, return, and adapt in everyday life. These core processes—acquisition, extinction, spontaneous recovery, generalization, and discrimination—explain much of our learned behavior.

Acquiring a New Association

acquisition

Acquisition is the initial stage of learning in conditioning when a neutral stimulus becomes linked with an unconditioned stimulus (UCS).

During this period, the neutral stimulus gradually begins to trigger the response on its own and becomes a conditioned stimulus (CS).

Key features of acquisition

  • The timing between the CS and UCS matters.
  • For most types of conditioning, the CS should occur briefly before the UCS—sometimes within just a few seconds (Chance, 2009).
  • Some forms of learning allow for much longer intervals.

Predictability matters: The Rescorla–Wagner Model

Robert Rescorla demonstrated that an organism learns best when the CS is a reliable predictor of the UCS. Consider these two situations: 

  • Ari’s experience: Dinner is always at 6:00. The time reliably predicts food → Ari becomes hungry before 6:00.
  • Soraya’s experience: Dinner time varies daily → 6:00 is not a reliable predictor → no strong conditioned response.

Rescorla, along with his colleague at Yale University, Alan Wagner, developed a mathematical formula that could be used to calculate the probability that an association would be learned given the ability of a conditioned stimulus to predict the occurrence of an unconditioned stimulus and other factors; today this is known as the Rescorla-Wagner model (Rescorla & Wagner, 1972) (Rescorla & Wagner, 1972).

A Special Case: Taste aversion

Taste aversion shows that classical conditioning can occur after a single pairing, and even with hours between the CS and UCS.

For example, say you eat chicken curry at lunch, later become ill with stomach flu, and then feel sick whenever you smell curry—even though the food wasn’t the cause.

This powerful one-trial learning is thought to be an evolutionary adaptation that helps organisms quickly avoid toxic foods (Garcia & Koelling, 1966; Garcia & Rusiniak, 1980).

Garcia and Koelling (1966) showed not only that taste aversions could be conditioned, but also that there were biological constraints to learning.

In their study, separate groups of rats were conditioned to associate either a flavor with illness, or lights and sounds with illness. Results showed that all rats exposed to flavor-illness pairings learned to avoid the flavor, but none of the rats exposed to lights and sounds with illness learned to avoid lights or sounds. This added evidence to the idea that classical conditioning could contribute to species survival by helping organisms learn to avoid stimuli that posed real dangers to health and welfare (Holmes, 1993; Jacobsen et al., 1993; Hutton, Baracos, & Wismer, 2007; Skolin et al., 2006). 

Breaking the Association

Once we have established the connection between the unconditioned stimulus and the conditioned stimulus, how do we break that connection and get the dog, cat, or child to stop responding?

Once a learned association exists, it can fade if the CS is repeatedly presented without the UCS.

extinction

Extinction is the gradual weakening and disappearance of the conditioned response (CR). For example:

  • Tiger the cat hears the can opener (CS) but no longer gets food (UCS). Over time, her excitement fades and eventually stops.
  • Pavlov observed the same pattern with dogs: ringing the bell without giving food caused salivation to decrease across trials until it stopped.

Spontaneous Recovery: When the Response Returns

Even after extinction occurs, the learned response can suddenly return.

spontaneous recovery

Spontaneous recovery is the return of a previously extinguished conditioned response following a rest period (Figure 1).

A chart has an x-axis labeled “time” and a y-axis labeled “strength of CR;” there are four columns of graphed data. The first column is labeled “acquisition (CS + UCS) and the line rises steeply from the bottom to the top. The second column is labeled “Extinction (CS alone)” and the line drops rapidly from the top to the bottom. The third column is labeled “Pause” and has no line. The fourth column has a line that begins midway and drops sharply to the bottom. At the point where the line begins, it is labeled “Spontaneous recovery of CR”; the halfway point on the line is labeled “Extinction (CS alone).”
Figure 1. This is the curve of acquisition, extinction, and spontaneous recovery. The rising curve shows the conditioned response quickly getting stronger through the repeated pairing of the conditioned stimulus and the unconditioned stimulus (acquisition). Then the curve decreases, which shows how the conditioned response weakens when only the conditioned stimulus is presented (extinction). After a break or pause from conditioning, the conditioned response reappears (spontaneous recovery).

For example:

  • Tiger stops responding to the can opener after months of no food pairings. When the can opener is used again to prepare her meal, she quickly becomes excited—showing the re-emergence of the conditioned response.
  • Pavlov’s dogs behaved the same way after a rest period: salivation returned even without new pairings of the bell and food.

Putting It Together: Acquisition, Extinction, and Spontaneous Recovery

Ice cream truck
Figure 2. If you develop an ice cream habit,  you may find your mouth watering just at the sight or sounds of the truck.

Of course, these processes also apply to humans. For example, let’s say that every day when you walk to campus, an ice cream truck passes your route. Day after day, you hear the truck’s music (neutral stimulus), so you finally stop and purchase a chocolate ice cream bar. You take a bite (unconditioned stimulus) and then your mouth waters (unconditioned response). This initial period of learning is known as acquisition, when you begin to connect the neutral stimulus (the sound of the truck) and the unconditioned stimulus (the taste of the chocolate ice cream in your mouth).

Acquisition

  • Jingle (CS) → ice cream taste (UCS) → salivation (UCR)
  • After several pairings, the jingle alone causes salivation (CR).

Extinction

  • For several days, you hear the jingle but don’t buy ice cream.
  • Your salivation response decreases and eventually stops.

Spontaneous Recovery

  • After a weekend without hearing the truck, the Monday morning jingle triggers salivation again—even though no new learning occurred.