Classical Conditioning: MechanismsClassical Conditioning: Mechanisms

The general outline for this section:

I. What makes for an effective CS and/or US?

II. What is learned in classical conditioning?

III. Blocking and surprisingness

IV. Formal Models of Learning

I. What makes for an effective CS and/or US?

A. Novelty

CS-preexposure effect (or, latent inhibition)

Various explanations, depending on who you talk to

B. Intensity

C. Salience

D. Relevence

Remember Garcia’s studies?

Here’s a more elaborate version of it:

Phase 1

Group 1

Group 2

Bright/noisy/tasty water

Bright/noisy/tasty water

Phase 2 Test

SHOCK

X-RAY

Taste?

A/V?

Taste?

A/V?

X

X

Neither CS nor US salience could account for the idiosyncratic results obtained….

Flies in the face of the “arbitrariness” of learning associations...

CS/US distinctions: The concept of “biological strength”

Pavlov was the first to propose a distinction between CS’s and US’s

e.g.: a light or tone does not initially possess much biological strength, whereas food or shock does

Low Biological Strength = CS’s; High = US’s

Implications of Pavlov’s notion:

1) Higher-order conditioning

-once a CS--US association is formed, the CS now has more biological strength

2) Strong—weak ordering should result in no learning

e.g.: food--light

Also: higher strength of the US “energizes” learning

Problems with Pavlov’s notion of biological strength:

1) CS-preexposure effect -since no US, no learning should take place, according to Pavlov

2) Sensory Preconditioning

-learning does appear to occur with two “weak” stimuli

e.g.: light + tone tone + food light?

(notice that it is really higher-order conditioning in reverse)

So, while the existence of stimuli possessing biological strength is not debatable, where it fits into the big picture of how learning takes place is still in question

representation

S-S

S-R

The Evidence:

-Browne (1976): vicarious learning

-devaluation studies (e.g. Rescorla, 1973)

CS US representation

Response representation

II. What is learned in classical conditioning? (representations)

A typical example of a devaluation study (from Rescorla, 1973):

Phase 1 Phase 2 Test

E group

C group

Light--loud noise

Light--loud noise

Habituate noise

Don’t habituate

Suppression to light?

More suppression in C group than in E group

Suppression to light?

Serves as a test between S-S, S-R: if devaluation occurs, S-S supported

representation

S-S

S-R

CS US representation

Response representation

Devalued response to US

More devaluation studies:

Phase 1 Phase 2 Test

gp. E tone + food

tone + foodgp. C

food + rotate

rotate

Tone?

Tone?

Found evidence of devaluation: rotation contingent on food showed less activity than uncorrelated rotation

E

C

Phase 1 Phase 2 Phase 3 Test

Red--food

Red--food Green--Red

Green--Red

Red--000

Evidence of devaluation (S-S): E-group pecks less than C group

000

Green?

Green?

Devaluation not restricted to rats, nor to illness as the devaluing technique

However, not all devaluation studies support an S-S representation:

E

C

Phase 1 Phase 2 Phase 3 Test

Light + food

Light + food

Tone + Light

Tone + Light

food + rotate

rotate

Tone?

Tone?

No devaluation here: nonsignificant differences between the two groups

E

C

Phase 1 Phase 2 Phase 3 Test

Light + shock

Light + shock

Tone + Light

Tone + Light

Light----000

000

Tone?

Tone?

Again, no devaluation; tone is equally suppressive for the two groups

So, sometimes devaluation does occur (supporting S-S), sometimes it does not (supporting S-R)

WHY?!?!

Potential explanation: Konorski’s distinction

Stimuli can be internally represented in more than one way:

1) Sensory properties

2) Affective/Motivational properties

---- consummatory response

---- preparatory response

light---food = a sensory code (“food!”),

tone---light = a motivational code (“something good”)

If you devalue the food, it will not change the representation pointed at by the tone. (the light means different things in the two cases)

Reasons S-S is considered correct:

1) Konorski’s ideas provide an explanation for why devaluation did not occur, but leave intact the idea of an S-S representation taking place

2) S-R proponents have no good explanation for when devaluation studies work!

3) S-R “support” = no devaluation. In other words, it is asserting the null hypothesis!

4) Browne’s vicarious learning study

Conclusions: S-R “support” is really a lack of evidence at all,

S-R cannot explain Browne, nor when devaluation works

S-S can explain Browne, when devaluation works, and even when it doesn’t work (thanks to Konorski)

So, it appears S-S representations are the clear winners