Mazur Chapter 4: Theories and Research on Classical Conditioning Flashcards Preview

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The Blocking Effect


Conditioning is not an automatic result when a CS and the US are paired

Conditioning will occur only if the CS is informative, only if it predicts something important, such as an upcoming shock

This view seems to imply that the subject has a more active role in the conditioning process than was previously thought


Theoretical basis of the blocking effect


Kamin performed experiment with rats with compound stimuli and shock [d.v.= fear as measured by suppression of behavior]

Phase 1
• Blocking group received light paired with shock
• Control received no stimuli

Phase 2
• Both groups received compound CS of light and tone paired with shock

Test phase
• Both groups received tone alone, with no shock
• Blocking group displayed no fear
• Control group displayed fear

Kamin concluded that the prior conditioning with the light somehow “blocked” later conditioning of the tone

Simple explanation: the tone was redundant in the blocking group – it supplied no new information


The Rescorla-Wagner Model


A mathematical model designed to predict the outcome of classical conditioning procedures on a trial-by-trial basis

Learning will occur only when the subject is surprised, that is, when what actually happens is different from what the subject expected to happen

Always 3 possibilities in conditioning trials:
excitatory conditioning
inhibitory conditioning
no conditioning and all

Which of these three possibilities actually occurs depends upon:
• The strength of the subjects expectation of what will occur
• The strength of the US that is actually presented


Six Rules of the Rescorla-Wagner Model

  1. If the strength of the actual US is greater than the strength of the subjects expectation, all CSs that were paired with the US will receive excitatory conditioning
  2. If the strength of the actual US is less than the strength of the subjects expectation, all of the CS is that were paired with the US will receive some inhibitory conditioning
  3. If the strength of the actual US is equal to the strength of the subjects expectation, there will be no conditioning
  4. The larger the discrepancy between the strength of the expectation and the strength of the US, the greater the conditioning that occurs (either excitatory or inhibitory)
  5. More salient CSs will condition faster
  6. If two or more CSs are presented together, the subjects expectation will be equal to their total strength (with excitatory and inhibitory stimuli tending to cancel each other out)

Rescorla-Wagner: Acquisition


With each successive conditioning trial, the expectation of the US following the CS should get stronger, and so the difference between the strength of the expectation and the strength of the US gets smaller

Therefore, the fastest growth in excitatory condition occurs in the first trial, and there’s less and less additional conditioning as the trials proceed.

When the CS elicits an expectation that is as strong as the US, the asymptote of learning is reached, and no further excitatory conditioning will occur with any additional CS-US pairings


Rescorla-Wagner: Blocking


When two CSs are presented, the subject’s expectation is based on the total expectations of both

No conditioning occurs to the added CS because there is no surprise – the strength of the subject’s expectation matches the strength of the US

Increasing the size/strength of the US when presenting the compound CS may prevent blocking effects


Rescorla-Wagner: Extinction and Conditioned Inhibition


The strength of the expected US is greater than that of the actual US, leading to a decrease in the association between the CS and the US

This leads any CS or compound CS to acquire some inhibitory conditioning


Rescorla-Wagner: Overshadowing


For a compound CS consisting of one intense stimulus and one weak one, the intense CS becomes more effective

The weak CS could elicit CRs on its own [given enough pairings with the US], but it is overshadowed when presented with the intense CS

Therefore the weak CS elicits little if any conditioned responding


Rescorla-Wagner: The Overexpectation Effect


When two CSs that elicit CRs on their own are combined, the expected US of the compound CS is roughly equal to their total strength

Compared to what it actually receives [the same US that follows the compound CS], the animal has an overexpectation about the size of the US, and both CSs will experience some inhibitory conditioning

Based on the frequency principle, it would not be expected that more CS-US pairings would result in a weakening of CS-US associations, yet this occurs in conditions like these where compound CSs experience inhibitory conditioning from due to the overexpectation effect


Theories of Attention


A common feature of these theories is the assumption that the learner will pay attention to informative CSs but not to uninformative CSs

These theories might also be called theories of CS effectiveness, because they assume that the conditionability of a CS, not the effectiveness of the US, changes from one situation to another


CS preexposure effect


Classical conditioning proceeds more slowly if a CS is repeatedly presented by itself before it is paired with the US

Because the CS predicts nothing during the preexposure, attention to the CS decreases, and so conditioning is slower when the CS is first paired with the US at the beginning of the conditioning phase

The Rescorla-Wagner model does not predict the CS preexposure effect
• One a new CS is presented by itself, the expected US is zero, and the actual US is zero

According to the Rescorla-Wagner model, since the actual US equals the expected US, there should be no learning of any kind

However, subjects evidently do learn something on CS preexposure trials, and what they learn hinders their ability to develop a CS-US association when the two stimuli are paired at a later time


Comparator Theories of Conditioning


Comparator theories assume that the animal compares two likelihoods:

The likelihood that the US will occur in the presence of the CS

The likelihood that the US will occur in the absence of the CS


Though similar to Rescorla-Wagner, Comparator theories differ in two ways:

  1. They do not make predictions on a trial-by-trial basis
    • They assume what is important is not the events of individual trials but rather the overall long-term correlation between a CS and the US
  2. They propose that the correlation between CS and US does not affect the learning of a CR but rather its performance
    • e.g. Subjects may learn an association between a CS and a US that cannot initially be seen in their performance, but this learning can be unmasked if the strength of a competing CS is weakened

Instead, comparator theories assume that both the CS and contextual stimuli have acquired equal excitatory strengths, because both have been paired with the US

Comparator theories also assume that a CS will not elicit a CR unless it has greater excitatory strength than the contextual stimuli

The animal has learned something about the CS: that the US sometimes occurs in its presence, but the animal will not respond to the CS unless it is a better predictor of the US than the context


Rescorla-Wagner, Attentional and Comparator Theories: Common Theme


The predictiveness or informativeness of the stimulus is a critical determinant of whether a CR will occur

And the predictiveness or informativeness of a stimulus cannot be judged in isolation

It must be compared to the predictiveness of other stimuli also present in the learner’s environment.


First- and Second-Order Conditioning


Using US devaluation conditioning, Holland and Rescorla found that S-S associations are formed in the first-order conditioning, but that S-R associations are formed in second-order conditioning

[Not 100% of the time—S-S associations are sometimes found in cases of second-order conditioning]


Associations with Contextual Stimuli


When a stimulus is repeatedly presented in one experimental chamber, an association can develop between the contextual stimuli and that stimulus
o e.g if a light is occasionally presented in the chamber, the animal may form a context-CS association, and we might say the animal learns to ‘expect’ the light when it is placed in the chamber.

Because the light is no longer a surprising stimulus, it becomes harder to condition if it is now paired with a US (CS preexposure effect)

It is also been shown that if an animal first learns a context-US association, this can interfere with the acquisition of a CS-US association


Sensory preconditioning


Two CSs are repeatedly paired before the US is introduced

Provides further evidence for the existence of S-S associations

Shows that these associations can form between two “neutral” stimuli as well as between a CS and a US


Occasion Setting


Under certain circumstances, a stimulus can control a CR in an indirect way

It can determine whether the subject will respond to another CS

It regulates the CR by signaling those occasions on which the CS will be followed by the US

The Occasion Setter acts as a sort of switch that must be turned on to complete the connection between the CS and the US

*different from ordinary excitatory or inhibitory CSs


The Contiguity Principle and Taste-Aversion Learning


It has been found that taste aversions can be acquired by many different species when the CS-US interval is several hours long

Because the effect of CS-US intervals are many times longer than a traditional experiments on classical conditioning, some have proposed that taste-aversion learning is a special type of learning, one that does not obey the principle of contiguity

Long-delay learning, however is not unique to taste aversions, and though intervals are longer, phenomena such as generalization gradients, extinction, conditioned inhibition, blocking, second-order conditioning have all been observed in taste-aversion learning


equipotentiality premise


A given stimulus will be an equally good or bad CS in all contexts

The experimenter’s choice of stimuli, responses, and species of subject is relatively unimportant

Not all stimuli and all responses will result in equally rapid learning

Stimuli differ in their conditionability, but a stimulus or response that is difficult to condition in one context should also be difficult condition in other contexts

  • *Evidence has shown the equipotentiality premise to be wrong…

Garcia and Koelling (1966) showed that the same two stimuli can be differentially effective in different contexts

Taste was a more effective stimulus when the aversive event poison, but in audiovisual stimulus was more effective when the aversive event was shock

**Before we can predict the strength of a CR, we must know something about the relationship between the CS and the US


prepared associations



CS-US associations that are able to be formed quickly due to an innate propensity

difficulty forming associations: innate contraprepared associations

no special disposition: unprepared association

**To predict how effective a particular CS will be, it is not enough to know how effective this CS has been in other contexts

***We must also know what US will be used and whether this CS-US pair is an example of a prepared, unprepared, or contraprepared association


Biological Preparedness in Human Learning


People can also develop a strong aversion to a food that is followed by illness, even if the illness follows ingestion of the food by several hours

In many cases, people develop an aversion to some food even though they know that their illness was caused by something completely unrelated to the food

Humans have a predisposition to develop fears of things that have been dangerous to our species throughout our evolutionary history, such as snakes, spiders, and thunder

There is also evidence that people have the ability to detect a snake or spider individual array faster than they can detect more neutral stimuli such as flowers and mushrooms


Drug Tolerance and Drug Cravings As Conditioned Responses


When a CR is the opposite of the UR, it is sometimes called a compensatory CR, because it tends to compensate for, or counteract, the UR

Drug tolerance is due, at least in part, to a compensatory CR that is elicited by CSs that regularly precede a drug administration

These CSs may include:
o contextual stimuli
o the stimuli associated with drug administration,
o even the early bodily sensations that occur when a drug starts to produce its effects in the body


Siegel: Drug Tolerance in Rats


Siegel found that a decrease in analgesia over successive morphine injections was controlled by contextual stimuli

According to Siegel’s hypothesis, this tolerance occurred because the contextual stimuli that accompanied each morphine injection acquire the capacity to elicit a compensatory CR of hyperalgesia, or an increased sensitivity to pain

If a rat’s tolerance to a drug such as morphine is indeed a CR, it should be possible to extinguish this response by presenting the CS (the context) without the US (morphine), and this was shown in subsequent research

Environmental stimuli can also produce drug cravings and withdrawal symptoms


cue exposure treatment


Clients are exposed to stimuli normally associated with the drug (without the drug), so that condition drug cravings can be extinguished, often in several settings


Siegel, summary of drug tolerance findings


Siegel has found evidence that drug tolerances to, at least in part, to the acquisition of compensatory CRs that tend to counteract the effects of the drug itself.

Stimuli associated with the drug that enlist these compensatory CRs, are commonly called cravings of withdrawal symptoms

Many cases of drug overdose reactions may occur when a habitual drug user takes the drug in a new or unfamiliar setting

Some of the biggest obstacles to remaining absent after drug treatment are the cravings CSs in the individual’s environment


conditioned opponent theory (Schull)


Theory which deals exclusively with the conditioning of b-processes:

Any increase in the size of the b-process is based on classical conditioning.

[Differs from Solomon and Corbit, who proposed that the b-process in increased by a non-associative strengthening mechanism]

Only the b-process is conditionable, and it can combine with contextual stimuli to counter the a-process


sometimes opponent process (SOP)


Wagner’s theory that is meant to apply to all CRs, whether or not we would call them “b-processes”

Theory predicts that in some cases a CR will be the opposite of the UR, but in other cases a CR will mimic the UR

The CR will mimic the UR if the UR is monophasic—no rebound effect
• e.g. eyeblink

CR will be the opposite of the UR if the UR is biphasic
• e.g. heart rate UR is biphasic because it consists of a increase in heart rate when the shock is on, followed by a decrease in heart rate below baseline when the shot is terminated

Because the UR exhibits such a rebound effect, SOP predicts that the CR will be the opposite of the UR


Physiological Research on Classical Conditioning

  1. The neural pathways involved in the CR are often different from those involved in the UR
    o e.g. UR eyeblink to an air puff the seems to be controlled by two distinct pathways – a fairly direct pathway the brainstem, and a more indirect pathway passing to the cerebellum
    • whereas the CR eyeblink is controlled solely by cerebellar pathway
  2. Many different brain structures may be involved in the production of a simple CR
    o based on PET and fMRI scans showing activation in various regions
  3. Different conditioning phenomenon may involve different brain locations
    o e.g., removal of the hippocampus will result in lack of a blocking effect, but does not prevent development of conditioned inhibition
  4. Different CRs involve different brain locations
    o e.g. a damaged cerebellum prevents eyeblink CR, but SCRs and heart rate measurements showed they had indeed learn the association between the CS and the air puff
  5. Individual neurons have been found whose activity appears to be related to the acquisition of CRs