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
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Prof. Stephan Anagnostaras
Lecture 2: Learning Theory
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
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.
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.
• The stronger the US,
the stronger the CR
(same growth rate)
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
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)
• Discrimination explained using learning theory
• Extinction explained
• 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
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)
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
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.
Forward works best. Interestingly this is a test of
Delay conditioning is another term for forward conditioning.
Trace conditioning is quite special in terms of mechanistic models of animal learning.
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
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
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.
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
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
• 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
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
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
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
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)
with CS-US delay
of up to 75 min
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
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.
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!
“Bright Noisy Water Experiment”
Biological constraints on learning
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.
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?
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.
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.
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.
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)
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.
Can explain a number of phenomena:
Blocking (A+, AB+, … B)
Unblocking (A+, AB++, …B)
Conditioned Inhibition (A+, AB–, … B)
• 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