Lecture 3 Flashcards
What is the rescorla-wagner model?
mathematical expression of surprise
- learning will occur only when the subject is surprised - that is, when what happens is different from what the subject expected to happen
What is blocking?
Participants are not surprised because they’ve already learned that the light predicts the shock
- doesn’t produce a stronger conditioned stimuli but refers to the lack of responses to the second stimulus in phase 2
Explain the steps involved in blocking
Phase 1.
Blocking: L–> US
Control: nothing
Phase 2.
Blocking: L & T –> US
Control: L & T –> US
TEST:
Blocking: no CR
Control: CR
Why is the blocking experiment important?
Shows that:
- conditioning is not an automatic result of CS-US pairings
- for conditioning to occur, the CS must be informative and US surprising
What can we use to quantify the level of surprise?
deltaV = Vmax - Vn
where:
V = associative strength between CS and US
Vmax = maximum associative strength
delta V = change in associative strength on each conditioning trial
When does the most amount of learning occur?
delta V
- at the beginning of conditioning
- -> more surprised by the US at this time
Why do we care how surprising the US is?
So we can predict what is biologically meaningful
- and we can learn to avoid or work for these
Learning curves differ in terms of?
Vmax and rate of acquisition
How does Vmax differ in learning curves?
- asymptote level can change - determined by magnitude of US
- more incentive = higher Vmax
How does rate of acquisition vary between learning curves?
- gradual = little learning over certain amount of time
- steep = learning is almost immediate (e.g. food avoidance)
What is alpha related to?
the importance of the CS
What is beta related to?
the importance of the US
Which values change with conditioning?
Vn and deltaV
- Vn gets bigger
- delta V gets smaller
Formula for acquisition of a conditioned response
deltaVn = alphabeta(Vmax-sumofVn)
What is the extinction of a conditioned response
the weakening of a conditioned response when a CS is presented by itself
- Vmax = 0
What type of associative strength do conditioned inhibitors have?
negative
Explain blocking using Rescorla-wagner model
- when 2 CSs are used, the association or expectation at the beginning of the trial would be the sum the strengths of each stimuli present
- therefore the amount of conditioning on a compound trial in which A and B occur together would be:
= alphabeta(Vmax-sumVofA&B)
- the shock stays the same, therefore so does Vmax in compound conditioning (V= sum of light and tone = 1)
- change in learning as a result of extra conditioning trial with new tone but same light, new learning = 0
In blocking - what if the US is different in compound conditioning?
Then learning would happen - if US is bigger = Vmax will be bigger
Explain the over-expectation effect
- tone –> shock
- light –> shock
- tone + light –> shock
- US doesn’t change, animal will predict something that doesn’t happen (over-expected shock to occur)
Assume only a few trials were given before the compound trial, what is the result?
the model predicts an increase in associative strength for both T and L when presented during the compound trial
What if there is extensive training prior to the compound trial?
the model predicts a decrease in associative strength for both T and L when presented during the compound trial
Explain compound training in rats (tone and light –> shock)
Phase 1.
experimental group: tone + light –> shock
control: nothing
Phase 2.
both groups: tone –> shock; light –> shock
= much more fear associated with light
Why is there more fear associated with shock and light rather than shock and tone?
More natural to associated foot shock with a light
What would the result be in the US is not contingent with the CS?
conditioning will be strong to contextual cues but not to the CS
Explain contextual association
trial 1. CS + context –> US = positive associative strength to compound
trial 2. context alone –> US = positive associative strength to context
trial 20. CS + context –> US = negative associative strength to compound
trial 21. context alone –> US = positive associative strength to context
= at first, fear to both but as conditioning continues, fear to CS decreases and fear to context increases to Vmax
- CS becomes a poor predictor of US
Some problems with Rescorla-Wagner Model:
- exclusive focus on the “surprisingness” of the US
2. the conclusion that extinction removes the original learning
What is spontaneous recovery?
the reappearance of a CR to a CS after a period of time following the last extinction trial
What is renewal?
the reappearance of a CR to a CS due to the return of the training environment, instead of the environment used during extinction
What is reinstatement?
the reappearance of a CR to a CS due to a brief presentation of the US
- potato chip effect (just a little taste)
What is rapid reacquisition?
rapid return of a CR to a previously extinguished CS (reason associated with relapse)
- something that is learned initially comes back so much faster the second time around
What is prediction error?
Learning
- gets smaller with conditioning trials
What is dopamine?
a neurotransmitter involved in learning motivation and a variety of psychobiological functions
Dopamine agonist
blocks the reuptake of dopamine –> enhance effects
- “more”
Dopamine antagonist
blocks the effect of dopamine –> removal of dopamine effects
- “less”
Who studied stimulation of the VTA in chimps?
Wolfram Schultz
Prior to CS-US conditioning:
no prediction; reward occurs
After CS-US conditioning:
reward predicted; reward occurs
- no response at reward, but shifts to CS
During extinction:
reward predicted; reward does not occur
- silencing of herons = computing prediction error
What is auto-shaping?
CS associated with the delivery of a US
- Sign tracking
- goal tracking
Explain sign tracking
- pays attention to CS
- response towards US declines
- dopamine shifts activity (US –> CS)
E.g. rat goes toward light
Explain goal tracking
- not learning predictor of US
- fails to respond to CS
E.g. rat going towards where food is delivered
Response of dopamine - when is a stimulus pleasurable?
Only when it isn’t predicted
Dopamine acts as the?
learning signal
- not the actual learning
What region receives dopamine from VTA?
nucleus accumbens
Which of the following about dopamine is false?
- it plays a role in the acquisition of CS-US associations
- it encodes prediction error
- it is increased by pleasurable stimuli
- it is released in the nucleus accumbent during CS-US learning
it is increased by pleasurable stimuli
In autoshaping?
the CS is associated with the delivery of the US
Activity of dopaminergic neurons in the ventral segmental area should increase when a:
a well conditioned CS is present
Extinction is?
the acquisition of competing or alternative learning
Rats in the random group described by Rescorla:
associate the US with background/contextual cues
Assuming alpha/beta = 1 and V5 = 1, the value of deltaV after the first extinction trial is?
-1
According to the rescorla-wagner model, whether conditioning will occur or not depends on the relationship between?
Vn and Vmax
The blocking phenomenon is said to occur when?
nothing is learned about a novel stimulus despite compound training with an established excitatory CS
