Chapter 4

• Classical Conditioning: Mechanisms– What makes effective conditioned and

unconditioned stimuli?– What determines the nature of the

conditioned response?– How do conditioned and unconditioned

stimuli become associated?

What determines the nature of the CR?

Classical conditioning is defined by the development of a CR to a previously neutral CS

Look at why particular responses become conditioned

The first explanation for the nature of the CR is the Stimulus Substitution model

The Stimulus Substitution Model

• developed by Pavlov

• the association of the CS with the US turns the CS into a ‘surrogate’ US

• the CS activates neural circuits previously activatedonly by the US and elicits responses similar to the US

• with pairings of the CS and US, a new connection develops between the neural circuits previously activated by the CS and the neural circuits previouslyactivated only by the US

US center

CS center

Response center

Diagram of Pavlov’s Stimulus Substitution Model

• Conditioning enables the CS to elicit the UR

• The CS substitutes for the US

The US as a determining factor for the CR

• The quality or nature of the US affects the type of CR

• Different USs elicit different URsL Food; elicits salivationL Shock; elicits fear response

• More subtle differences in CRs depending on the USKL FoodKL water

• Pigeons peck at the KL in both cases but the pecking response is different

• Thus, the form of the CR resembles the form of the UR

Learning & Homeostasis

• The concept of Homeostasis was introduced by Water Cannon

• certain physiological responses are maintained at acceptable levels (temp., HR, BP)

• change in one direction must be accompanied by an opposite response to return the system to a baseline oroptimal level

• operates through a negative feedback loop• i.e., a drop in temp. is detected and serves as a stimulus to activate compensatory responses

Learning & Homeostasis

• Homeostatic mechanisms operate by a negative feedback process that counteracts a challenge after the disturbance has already caused a deviation fromhomeostatic level

• Pavlovian conditioning can be beneficial to anticipate the challenges to homeostasis and start compensatorymechanisms earlier

Learning & Homeostasis

• For ex., exposure to cold Feedback processes require a drop in temp. beforecompensatory responses (shivering, vasoconstriction)occur to counteract the cold

• If subjects learn which cues signal when they will getcold, they can make feed-forward compensatory adjustments in anticipation of the cold and avoid the actual drop in temp.

Conditioned Homeostatic Responses

• examined most extensively with psychoactive drugs

• Conditioning model of drug tolerance

• tolerance = repeated presentations of the drug have progressively less effect

• administration of a psychoactive drug causes physiological changes that disrupt homeostasis = US

• these physiological changes caused by the drug triggerunconditioned compensatory changes to counteract thedrug = UR

Conditioned Homeostatic Responses

• stimuli that accompany drug administration becomeassociated with the drug (syringe, context cues, etc…)

• these cues associated with drug administration triggerthe compensatory response, so the drug has less effect

• the CR then counteracts the drug effect

The CS as a determinant of the form of the CR

The quality or nature of the CS affects CR, even thoughthe CS is supposed to be innocuous or neutral

Experiment by Holland with rat subjects

Tone Food T elicits headjerk behavior (rapid back and forth movements of the head)

Light Food L elicits rearing and investigationof the food cup

The CS as a determinant of the form of the CR

Timberlake and Grant (1975) – described in textbook

Investigated classical conditioning in rats with food as the US

The CS was a presentation of another rat

Instead of gnawing and biting (as stimulus substitutionmodel might predict), the CR was orientation, approach,sniffing and social contact

Conditioned Behavior and Behavior Systems

Presentation of a US activates the behavior system relevant to that US

- food activates foraging/feeding system- mate activates sexual behavior system

As a CS becomes associated with the US, it becomes integrated into that behavior system

The form of the CR will depend on the CS-US interval that is used

The CS-US interval determines where the CS becomes incorporated into the sequence of responses that makes up the behavior system

General searchbehavior

Focal searchbehavior

Consummatory behavior (copulation)

CS US

CS US

Sexual Behavior System

Atkins (2000)

Light Female quail•60 sec CS-US interval (male searched in area of light)•20 min CS-US interval (male searched all of chamber)

How does a CS produce responding? Some Different Views as to What is Learned in Classical Conditioning

a. S-S Learning

b. S-R Learning

S-S Learning Interpretation

States that the CS enters into an association with the US (or US representation)

The CS triggers a memory of the US which in turn elicits a response

Early Learning Trial

CSCS

US

US

U R

UR

An association begins to develop between?The CS center and the US center

CS-Only Test Trial

CS

CSUS

U R

CR

S-R Learning Interpretation

States that because the CS occurs close in time to the UR, it comes to trigger the response directly

An association forms between the CS and the response

Early Learning Trial

CSCS

US

US

U R

UR

An association begins to develop between?The CS center and the response UR

CS-Only Test Trial

CS

CS

U R

CR

S-S versus S-R Learning

S-R Learning

Support: studies where CR is identical to UR

Problem: sensory preconditioning

S-S Learning

Support: US-devaluation experiments

Problem: does not specify the nature of the CR

US-Devaluation Procedure

Phase Experimental Group

Control Group

Conditioning CS US CS US

US Devaluation e.g., CTA to chocolate

e.g., no exposure to US

Test/Result CS Decreased CR

CRCS

i.e., Devaluation of US in Experimental Group results in decreased CR relative to Control Group

Support for S-S theory comes from study by Holland

He showed that the memory of an event could substitutefor the event itself in the formation of a new association

Phase 1: T Wintergreen/sucrose

L Nothing

Phase 2: ½ got T LiCl

½ got L LiClPhase 3: Measured consumption of wintergreen

Results: Rats that had T - LiCl pairings consumedsignificantly less than rats that had L – LiClpairings

Explanation

According to Holland, the T in phase 2 calls up a representation or memory of the flavor and thismemory gets associated with the LiCl.

Even though the flavor was never paired with LiCl, we see an aversion because the T was paired with LiCl

The 2 stimuli essentially substitute for each other

Evidence for S-S theory

How do Conditioned and Unconditioned Stimuli Become Associated?

Contiguity

Two stimuli become associated if they occur close together in time

While contiguity is important, it is not sufficient for conditioning to occur

Contingency

Refers to the predictive relationship between stimuli

The CS has to convey information about US occurrence

p(US/CS) > p(US/no CS)

Rescorla’s (1968) Classic Experiment on Contingency

Method

Used the CER procedure with rats:

First phase, operant conditioning to establish steady bar pressing.

Second phase, CER training: classical conditioning to establish CER.

Method (continued)

CER training (daily for 5 days):

• All rats exposed to 12 tones (the CS).

• The tones were 2-min long and the mean inter-tone interval was 8 min.

• The probability of shock (the US) during the tone was .40 for all rats.

• Groups differed in the probability of shock during the inter-tone interval.

During the Inter-tone interval: • Group 0 : no shocks • Group .1: shocked with a probability of .1 • Group .2: shocked with a probability of .2• Group .4: shocked with a probability of .4

Method (continued)

ToneCS

US for Group:

0

.1

.4

.2

= Shock US in presence of Tone CS

= Shock US in absence of Tone CS

= 2 minutes of Tone CS

1 1 2 2 3 3 4 4 5 6 7 8 9 105 6 7 8 9 10Time

Third phase, after CER training, the rats were returned to bar pressing for food.

While the rats were bar pressing, the tones were presented as before, but no shocks were given

(what procedure is this?)

Conditioning was assessed by a suppression ratio (the lower the ratio, the greater the suppression, the stronger the conditioning).

Method (continued)

Rats that only experienced shock with the tone, showed total suppression.

Rats that experienced as many shocks in the absence of the tone as they did in its presence showed no suppression.

• These results suggest that contiguity is not the only associative principle necessary to produce learning.

• All rats experienced the same degree of contiguity between tone and shock, they differed in the extent to which the shock was contingent on the tone.

Problem for notion of contiguity and contingency

Blocking

• one of the more important phenomena in classical conditioning

• shows that simple contiguity between the CS and USis not sufficient for conditioning

• blocking experiments are typically done in 3 phases

Blocking

Group Phase 1 Phase 2 Phase 3

ExperimentalGroup (blocking)

ControlGroup

A US

Nothing

AB US

AB US

Test B

Test B

Same # trialsContiguityContingency

Blocking

In Control group, should get equal conditioning to both A and B

- both are equally contiguous with the US- same predictive relationship

What happens in the Blocking group?- if during phase 1, A perfectly predicts the US thenshould see little conditioning to B in phase 2- B adds no new information since the US is already predicted by A

B should evoke a stronger CR in the control group on test

This is called Blocking