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Neurobiology of Learning and Memory. Prof. Stephan Anagnostaras Lecture 2: Learning Theory. Classical (Pavlovian) conditioning. Twitmyer (1902) Paired bell with patellar tendon tap • Previously neutral bell could now elicit knee jerk

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Neurobiology of Learning and Memory

Prof. Stephan Anagnostaras

Lecture 2: Learning Theory


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Classical (Pavlovian) conditioning

Twitmyer (1902) Paired bell with patellar tendon tap • Previously neutral bell could now elicit knee jerk

Ivan Pavlov Studied digestion, and noticed that after he worked with a particular dog for a while, the dog salivated when it first saw him. Paired metronome with food • Previously neutral metronome elicited salivation. • Called this conditioning


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Classical (Pavlovian) conditioning

A conditional relationship emerged between the meaningful and previously neutral stimulus.

US - unconditional stimulus - biologically significant stimulus (food)

UR - unconditional response (salivation)

CS - conditional stimulus - previously neutral stimulus (bell)

CR - conditional response (salivation)

The UR and CR can be different, but it bears some relationship to the UR.


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Classical (Pavlovian) conditioning

After pairing, how do you know you have a CR?

Present the CS alone (without the US)

Measure the response at the beginning of the CS (metronome) before the US is presented (food)

• One theory is that the purpose of CSs is to predict USs and the CR is a prepatory response.


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Basic

Phenomena

Asymptote

•Negatively accelerating

growth curve

• The stronger the US,

the stronger the CR

(same growth rate)

Growth

rate


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Basic phenomena

1.Acquisition from CS–US pairings• the curve is negatively accelerating• the stronger US produces a higher asymptote• the CR gets stronger with repeated trials

2. Extinction• the CS is presented alone after conditioning• CS–• same curve as acquisition• not unlearning or erasing memory

3. Generalization• if you present a similar CS you will get a similar reaction• generalization decrement


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Basic phenomena

4. Discrimination• Train CS+ and CS– that are similar• Inhibition

Associative learning theory• Tries to explain what is going on and relies on 3 processes to explain everything

1. Excitation (excitatory association)

2. Inhibition (inhibitory association)

3. Generalization

• Discrimination explained using learning theory

• Extinction explained


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Basic phenomena

• Inhibition is a weaker process than excitation

• Spontaneous recovery in extinction

• Disinhibition in extinction

• Excitatory association not lost, it’s only the buildup of inhibition that suppresses excitation

• Law of parsimony

Power of a theory = # of things explained----------------------------# of explanatory principles


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Procedure, Process, & Behavior

Procedure = what we do (e.g., pair CS and US)

Process = what intervenes between procedure and behavior (e.g., excitation, inhibition)

Behavioral resultwhat we observe (e.g., after extinction we see a reduction of the CR)

• Our explanation involves all three

• Must be aware of this distinction -- procedure is not what is learned by the animal

• Skinner argued only talk about procedure-result laws (radical behaviorism)


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Control procedures

In order to study associative learning, must show change in behavior is due to pairing of the CS and US

• Presentation of stimulus alone increases CR:SensitizationControl: present the US alone

• Presentation of CS alone increases CRPseudoconditioning Control: present the CS alone


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Control procedures

How could we combine the two control groups?

Unpaired group receives both the US (sensitization) and CS (pseudoconditioning) but not together.

Alternative is the truly random control.

The main point is subject has same experience with CS and US as the Conditioning group.


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Several acquisition procedures

Forward works best. Interestingly this is a test of

Contiguity Theory


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Several acquisition procedures

Delay conditioning is another term for forward conditioning.

Trace conditioning is quite special in terms of mechanistic models of animal learning.


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Higher order conditioning

Second-order conditioningPhase I Phase II TestCS1-US CS2-CS1 CS2-->CRtone-food light-tone light

Sensory pre-conditioningPhase I Phase II TestCS2-CS1 CS1-US CS2-->CRlight-tone tone-food light


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Generality of conditioning

Conditioning permeates everything you docan condition pancreas and most glands, voluntary and involuntary muscles, and immune system

Coke (CS)-----> Sugar US----> UR (insulin release) …after a few pairings…Coke (CS) ---> CR (insuline release)

• Abrupt switch to Diet Coke can cause hypoglycemia

• Pavlovian conditioning prepares the body for impending URs


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Generality of conditioning

Hollis (1989)blue gouramis mating behavior - if a male enters territory drives it away

Exp 1:• Males were subjects• Training:Paired: light (CS) paired with access to males (US)Unpaired: light unpaired with access to males

Testing: the light was turned on and barrier removed. Paired male always won against unpaired male. But also drives away female.


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Generality of conditioning

Hollis (1989)Exp 2:Paired: light (CS) paired with access to females (US)Unpaired: light unpaired with access to females

Testing: get light then access to femaleResult: when light turned on paired group started mating much more rapidly than unpaired.

Exp 3: Design the same as #2, except female now in between paired and unpaired male -- female always picks paired male


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Generality of conditioning

Hollis (1997)

Exp 4: Reproductive success

Training: Paired got light with access to female for 2h, Unpaired got light unpaired with access.

Testing: present light then give access to female for 2 h for both groups. Six days later count baby gouramis


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xWhat is learned?

Emotional Learning

• Little Albert studyConditioned emotional response (CER)(Pavlovian fear conditioning)

Estes & Skinner (1941) Conditioned Suppression Trained to bar-press for food Paired tone with shock When tone came on fear suppressed bar-pressing

Suppression became the dominant way to measure CR


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What is learned?

Why not just measure fear?

• No attention to evolution. Why do rats stop bar-pressing? They freeze. Nowadays people just measure freezing or other defensive CR.

E.g. Fanselow & Bolles 1979: Did fear conditioning with backward (unpaired group)

• Evolution heavily influences what is learned, and even what can be learned


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What is learned?

S-S vs S-R

Two views on learning

S-S: CS--->US---> RS-R: CS--->R (US serves to stamp in this association)

Strong evidence for S-S learning:Rescorla (1973): Devaluation Experiment •Conditioned Suppression 1. Light (CS) paired with loud noise (US) 2. US alone - habituate (control = no habituation) 3. Test to CS - habituation group much less fear


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What is learned?

S-S vs S-R

Rescorla (1974) Inflation experiment 1. Tone-shock (0.5 mA)

2. US alone groups: - 3 mA - 1 mA - 0.5 mA - no shock

3. Test CS alone - little devaluation in 0.5 mA group - massive inflation in 1 and 3 mA groups

- Memory of the shock changed and CR changed


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What is learned?

What causes conditioning?

Contiguity theory: things have to occur together, that is necessary and sufficient

Challenges:• Simultaneous conditioning doesn’t work well

• Garcia & Koelling (1966) Conditioned Taste Aversion (CTA)


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Typical CTA Procedure

Good conditioning

with CS-US delay

of up to 75 min

-Contiguity not

necessary

Avoidance


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What is learned?

Is contiguity sufficient?

Kamin (1968): Blocking effectA= CS + = US AB+ = two different CSs with US

Train TestAB+ B alone = good conditioninglight-tone-shock light

However…Phase I Phase II TestA+ AB+ B alone = no conditioning!!

US must be SURPRISING. Note that contiguity is the same in both experiments


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What is learned?

Is contiguity sufficient?

Un Blocking effect

A= CS + = US AB+ = two different CSs with US

Phase I Phase II Test

A+ AB++ B alone = conditioning!!

Big US was SURPRISING.


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What is learned?

It is also surprising if you don’t get the US:

Conditioned inhibition procedure:Phase I Phase II TestA+ AB– B = cond inhibitor

US was expected but didn’t occur!


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Relationship between cue and consequence

  • Garcia & Koelling (1966)

    “Bright Noisy Water Experiment”

    • taste associated with illness

    • audio/visual stimuli associated with shock




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Garcia & Koelling

Biological constraints on learning


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Modern learning theory

Wagner, Logan, Haberlandt & Price (1968) Relative validity Theory

Two cmpd CSs: AX (tone, light),BX (buzzer, light)Animal sometimes get AX, sometimes BX

In group 1 (correlated conditioning group): AX is reinforced 100% (AX+) and BX is never reinforced (BX-)

In group 2 (the uncorrelated group): AX is reinforced 50% of the time, and BX is reinforced 50% of the time.


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Modern learning theory

In training…

Correlated group Uncorrelated Grp

AX = 100% reinf AX = 50%

BX = 0% BX = 50%

A predicts US neither A or B

B predicts no US perfectly predicts US

Both get 50% reinforcement overall. But what is happening to X? X is reinforced 50% of the time in both groups. According to contiguity theory should have the same conditioning. What happens?


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Modern learning theory

In test phase: Correlated gp Uncorrelated gp

A alone Strong cond No cond

B alone No Cond No cond

X alone No cond Strong cond

X has the same number of pairings in both groups, so contiguity theory is screwed

• Wagner says the cue must be the most valid predictor of the US in the situation in order to get associated. Relative validity to other CSs.


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Modern learning theory

Correlated group: A perfectly predicts shock, and X only half the time predicts shock

Uncorrelated group: A predicts shock half the time when its on, the same for B. But X predicts shock half the time whether A or B are on or not. So X is the most valid cue in this situation.


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Modern learning theory

Rescorla (1968), Contingency experiment

CS = tone, US = shock

For all groups, P (US|CS) = 0.8 (80% of the time you get the CS you will get the US also).

Rescorla varied the P(US|no CS) for all groups.



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Modern learning theory

Rescorla called this contingency theory:

If P(US|CS) > P (US|no CS) then excitatory conditioning

If P(US|CS) < P(US|no CS) then inhibitory conditioning

(e.g., safety signal)

If P(US|CS) = P(US|no CS) then no conditionin occurs

(truly random control)


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Rescorla-Wagner Model (1972)

Key Assumptions:

Emphasize CS-US pairings as criticial for conditioning

Formalize the notion of Kamin’s suprirse

Assume that any US can only support a limited amount of conditioning/reinforcement

All the CSs compete with echother for the limited amount of conditioning/reinforcement

Competition occurs through summation of all the CSs present on a given trial

•The US has a certain amount it can condition, meaning this is a US-limiting model.

•Stimuli compete for ability to predict the US.


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Rescorla-Wagner

Model (1972)


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Rescorla-Wagner Model (1972)

Can explain a number of phenomena:

Acquisition, extinction

Blocking (A+, AB+, … B)

Unblocking (A+, AB++, …B)

Conditioned Inhibition (A+, AB–, … B)

Contingency

• Can deal with a number of phenomena and makes several new predictions which were testable

• Cannot deal with latent inhibition (CS pre-exposure)

• Can deal with US pre-exposure effect


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