Blocking , Overshadowing and Shaping PDF

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Blocking , Overshadowing and Shaping...

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Pavlovian Conditioning: Blocking and Overshadowing

What do we learn:   

To expect the US: 2 lines of evidence OR New response (to CS same as US) o Stimulus substitution

New response vs expectancy 1: The CR   

CR=UR=Salivation CR not always same as UR o Shock conditioning: CR=fear, UR=pain CS produces anticipation of US

New response vs expectancy 2: US revaluation  

CS family=US chocolate (associated with new response) US overeats chocolate=illness (expect chocolate, revaluate feeling towards family)

Overshadowing:  

Stimuli compete for ‘associative strength’ Most ‘salient’ (noticeable) stimuli acquires most strength

Blocking: 

Rescorla & Wagner (1972): o Don’t learn if not surprised = no associations o Learn association to asymptote, blocks second weaker association o Related to learning curve = completely expect = no surprise = asymptote

Asymptote Fast Learning 

Explanation: o US supports certain amount of associative strength, shared between CS’s o A pretrained asymptote stimulus already has associative strength  Already associated with US  No strength left for other CS’s, pretrained CS=US not surprising

Mechanisms of learned behaviour

Shaping:   

Emergence of new behaviours following reinforcement of successive approximations (shift criteria) Teaches complex behaviour/ different to existing repertoire Through stimulus control: o Thorndike: automatically elicit behaviour?  Suggests no devaluing effect once response learned o Goal-directed, reward associated?

Occasion setting, Rescorla (1991):  

Not stimulus-outcome, associated with both outcomes Not stimulus-response, associated with both responses

Actions and Habits: Packard & McGaugh (1996): 



Condition 1: o Rat in cross, find food, trained by repeating o Edit starting point: goal=alter route / habit=same directions as before o Day 8: more goal, day 16: more habit Condition 2: o Deactivate caudate nucleus  Day 8: more goal  Day 16: more goal o deactivate hippocampus  Day 8: same goal/habit = chance  Day 16: bigger habit response...