blocking and extinction -L2 Mitchell Flashcards
what are associative links in blocking?
explained as failure to form a link
what is the prediction error in blocking?
A&B = CS’s, + = US
A+ then AB+
US is predicted by A by the end of A+ trials – no prediction error
US is not surprising on AB+ trials (no prediction error), so not processed
No B-US association learnt (AB+ trials are the only time B appears)
Learning about B is ‘blocked’ by A
why is blocking important?
Before blocking was discovered: it was believed that an association forms when two stimuli are paired
Hebbian learning (Hebb, 1949)
In blocking, Cue B -> US on AB+ trials, but there is little learning
Shows that learning isn’t just pairing of stimuli
Central to all contemporary learning theory
no prediction error on AB+ trials following A+ trials -> the US is not suprising
how can the US become unsuprising and less potent?
AB+ Blocking (A+ strong)
CD+ Overshadowing (Weaker A+)
(US is surprising on initial CD+ trials)
how can prediction error be formalised?
the difference between what you predict will happen and what actually happens
what is the Rescorla and Wagner 1972 formula?
ΔV = α(λ –ΣV)
ΔV = learning: change in associative strength on this trial – in this case we’re interested in the blocked cue B on AB+ trials
λ = total associative strength supported by outcome
ΣV = the expected outcome (given all cues present A&B)
α = attention to cues – this doesn’t change with learning
On AB+ trials, λ = ΣV, due to presence of the pretrained ‘blocking’ cue A
captures that you only learn when there is a prediction error
what is an alterative to r & w formula?
attention to CS’s
-Signals of important events are attended to especially well
The salience of the CS “α” is not fixed (contrary to R&W’s claim): α can change with experience/learning
Another way blocking might occur
what did Mackintosh 1975 predict?
blocking due to changes in attention to cues
-A+ then AB+
The most predictive cues will increase in salience/α (e.g., cue A)
Relatively less predictive cues will decrease in α (e.g., cue B on AB+ trials)
Not much learning about cue B
how can attention be measured?
eyetracking
what did Beesley & Le Pelley, 2011 research?
eye gaze in a learning task
-No shocks
-Present stimuli on the eyetracker screen
-Cues: chemicals (Addexium, Rezaline)
-Outcomes: symptoms in Mr X (itchiness, nausea)
tested AB plus and JK plus trials
what were the results of Beesley & Le Pelley?
Attention to cue A is high (it is a very good predictor of the outcome)
dwell times on pretrained cues were greater than on blocked cues across stage 2 training
Attention (eyegaze) to ‘blocked cue’ B is reduced compared to overshadowing controls J and K
Less attention/processing of Cue B would explain why there is less learning about that cue on AB-O1 trials.
how can blocking be summarised?
Blocking is seen in humans (e.g., Beesley & Le Pelley, 2011) and in non-humans (e.g., Kamin, 1969)
-Prediction error – no learning because US isn’t surprising on AB+ trials
Reduced attention to cue B on AB+ trials due to higher salience better predictor cue A
-salience mechanism in humans (Beesley & Le Pelley, 2011)
Blocking is not all about prediction error
why is extinction important?
Some aspects of extinction don’t fit with Rescorla Wagner
Clinical relevance: phobias and PTSD
what do extinction curves show?
Initial learning curve – US becomes less surprising over trials
Increase in associative strength slows down
Extinction curve – absence of US becomes less surprising over trials
Decrease in associative strength slows down
what are some limitations to Rescorla and Wagner?
Renewal
The CR returns in a different context from extinction -> extinction is context specific
Spontaneous recovery
The CR returns with a delay between extinction and test
true or false: extinction is specific to the context in which it was learnt
true
what did Bouton say on extinction?
Extinction is new learning of an inhibitory link
That inhibitory link only operates in the context in which it was learnt
Rescorla Wagner is wrong: The original CS-US link does not weaken
is exposure therapy and extinction the same?
Exposure therapy seems to be the same as extinction
Both show renewal and spontaneous recovery
How to avoid context specificity of exposure therapy (Laborda et al, 2011):
Have therapy in lots of different contexts
Spread exposure treatments over a long period of time
what is associative strength?
the strength of the connection between internal representations of the conditioned and unconditioned stimulus which determines the strength of the conditioned response
