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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
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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?
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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...
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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
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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
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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)
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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
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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
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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
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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)
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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
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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