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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?.

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chapter 4
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?
slide2
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

slide3
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 activated
  • only 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 previously
  • activated only by the US
slide4
Diagram of Pavlov’s Stimulus Substitution Model
  • Conditioning enables the CS to elicit the UR
  • The CS substitutes for the US
slide5
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 URs
    • L Food; elicits salivation
    • L Shock; elicits fear response
  • More subtle differences in CRs depending on the US
    • KL Food
    • KL 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
slide6
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 or
  • optimal level
  • operates through a negative feedback loop
    • i.e., a drop in temp. is detected and serves as a
    • stimulus to activate compensatory responses
slide7
Learning & Homeostasis
  • Homeostatic mechanisms operate by a negative
  • feedback process that counteracts a challenge after
  • the disturbance has already caused a deviation from
  • homeostatic level
  • Pavlovian conditioning can be beneficial to anticipate
  • the challenges to homeostasis and start compensatory
  • mechanisms earlier
slide8
Learning & Homeostasis
  • For ex., exposure to cold
  • Feedback processes require a drop in temp. before
  • compensatory responses (shivering, vasoconstriction)
  • occur to counteract the cold
  • If subjects learn which cues signal when they will get
  • cold, they can make feed-forward compensatory
  • adjustments in anticipation of the cold and avoid the
  • actual drop in temp.
slide9
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 trigger
  • unconditioned compensatory changes to counteract the
  • drug = UR
slide10
Conditioned Homeostatic Responses
  • stimuli that accompany drug administration become
  • associated with the drug (syringe, context cues, etc…)
  • these cues associated with drug administration trigger
  • the compensatory response, so the drug has less effect
  • the CR then counteracts the drug effect
slide11
The CS as a determinant of the form of the CR

The quality or nature of the CS affects CR, even though

the 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 investigation

of the food cup

slide12
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 substitution

model might predict), the CR was orientation, approach,

sniffing and social contact

slide13
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

slide14
Sexual Behavior System

General

search

behavior

Focal

search

behavior

Consummatory

behavior

(copulation)

CS US

CS US

  • 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)
slide15
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

slide16
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

slide17
Early Learning Trial

CS

US

CS

US

U R

An association begins to develop between?

The CS center and the US center

UR

slide18
CS-Only Test Trial

CS

US

CS

U R

CR

slide19
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

slide20
Early Learning Trial

CS

CS

US

US

U R

An association begins to develop between?

The CS center and the response UR

UR

slide22
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

slide23
US-Devaluation Procedure

Phase

Experimental Group

Control Group

US

Conditioning

CS

CS

US

US Devaluation

e.g., CTA to chocolate

e.g., no exposure

to US

Decreased CR

Test/Result

CS

CS

CR

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

slide24
Support for S-S theory comes from study by Holland

He showed that the memory of an event could substitute

for 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

LiCl

Phase 3:

Measured consumption of wintergreen

Results:

Rats that had T - LiCl pairings consumed

significantly less than rats that had L – LiCl

pairings

slide25
Explanation

According to Holland, the T in phase 2 calls up a

representation or memory of the flavor and this

memory 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

slide26
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
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
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.
method continued29
Method (continued)

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
slide30
ToneCS

US for Group:

0

.1

.2

.4

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

9

9

10

10

Time

= 2 minutes of Tone CS

= Shock US in presence of Tone CS

= Shock US in absence of Tone CS

method continued31
Method (continued)

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).

slide32
Rats that experienced as many shocks in the absence of the tone as they did in its presence showed no suppression.

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

slide33
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.
slide34
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 US
  • is not sufficient for conditioning
  • blocking experiments are typically done in 3 phases
slide35
Blocking

Group

Phase 1

Phase 2

Phase 3

Experimental

Group (blocking)

A

US

US

AB

Test B

Control

Group

AB

Nothing

US

Test B

Same # trials

Contiguity

Contingency

slide36
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 then

should 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

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