Pavlovian (classical) conditioning Flashcards
Pavlov initial experiment
food (UCS) –> salivation (UCR)
tuning fork (NS) –> no salivation (nonCR)
tuning fork + food –> salivation (UCR)
tuning fork (CS) –> salivation (CR)
pavlovian conditioning works
In all vertebrate species that have been tested; at least some invertebrates
For any CS an animal can detect (even a bell - though Pavlov probably never used one)
With spinal reflexes (e.g. in brain-damaged subjects)
In humans, e.g. eye-blink, GSR, knee-jerk - not used as much nowadays
common Pavlovian procedures
Eye blink to an air puff in humans, GSR
Key pecking in pigeons (“autoshaping”)
Taste aversion in rats (flavour plus illness)
Conditioned suppression (of lever pressing) in rats again
basic effects
- Stimulus Generalisation
- Extinction
- Overshadowing
- Blocking
stimulus generalisation
the further away from the initial CS the weaker the CR
e.g. touch, pitch, colour… – brighter/darker light, lower/higher pitch tone
see notes
extinction
Start with a well trained CS, then repeatedly present on its own – CR reduces
see notes
conditioned suppression
In this procedure the rat (typically) is trained to press a lever for food pellets.
After responding is established, the lever is withdrawn and the pairing of CS (e.g. light, tone) and US (normally shock) of interest takes place.
Then testing is performed with the lever back in the chamber.
The rate of responding during the CS (=RCS) and just before the CS (=Rpre-CS) is recorded, and a suppression ratio is calculated = “RCS” /”(RCS+Rpre−CS)” .
This measure has the property that for good conditioning it will approach 0, and for weak conditioning it will approach 0.5.
- lower score = stronger conditioning
overshadowing
Stage 1: Train compound of light and noise, or train the light and noise separately. For different groups use different intensities of noise (n=weak noise, N=intense noise).
Stage 2: Test the light and noise.
Mackintosh (1976)
Learning with noise overshadows the training with the light
Light also overshadows weak noise
Intense noise has some unconditioned properties as well – less of an effect of overshadowing
Train 2 stim together – one overshadows other and gains all the learning – usually more intense
see notes
blocking (Kamin, 1969)
Stage 1: noise →shock noise→ CR (fear)
Stage 2: noise + light → shock noise + light→ CR
Test: light light→ little suppression (0.45)
Surprise missing?
Control condition (no stage 1) gives suppression of 0.05 to the light on test.
With rats
Learnt very little from the light
Pre-training in stage 1 blocked learning to light in stage 2
see notes
blocking/overshadowing exp
A, B, C etc. are foods (Avocado, Bacon…). “+” means an allergic reaction. “?” asks for a rating – high = yes, low = no.
see notes
Class Results
The Y axis shows ratings. Higher means more likely to cause an allergic reaction. B shows blocking relative to C/D, and C/D show overshadowing relative to E.
The objection often made to demonstrations of this type is that people know what you’re doing, and you are testing their memory rather than their learning. We’ve recently addressed that point using an incidental paradigm in McLaren, Forrest, McLaren, Jones, Aitken and Mackintosh (2014, Neurobiology of Learning and Memory, on ELE). You still get overshadowing.
timing and conditioning
see notes
trace conditioning as a function of interval
Higher latency = better conditioning
4-8s = optimal conditioning
see notes
CS-US pairing not enough
Rescorla - “truly random control” (involves both partial reinforcement and free-US) leads to no conditioning despite some CS-US pairing: contingency is necessary
Kamin “blocking” - no acquisition when CS2 is paired with a US to which a strong CR to CS1 has already been established, if CS1 and CS2 are always presented together: is surprise necessary? – need learning to be novel – cannot be redundant
These and other phenomena were addressed by the Rescorla-Wagner theory
Rescorla-Wagner (R-W) learning rule
LEARN FROM TUTORIAL CARDS
see notes
Bear in mind that associative strength as computed by Rescorla-Wagner does not necessarily translate directly into responding – but we usually assume that the relationship between the two is monotonic. - see notes
contingency
Defined as p(O|R)-p(O|R’)
Wasserman et al. (1983)
In this experiment your task is to find out whether tapping a telegraph key (the response, R) has any effect on the occurrence of a white light (the outcome, O).
It is to your advantage to tap some of the time and not tap (this is R’) some of the time…
After each problem, choose a number on the -100 to 100 rating scale that best characterises the degree to which your tapping affected the occurrence of the white light.
The problems will be separated by a minute or two to allow you to make your rating.
Black – prob didn’t tap = .5
Blue – prob didn’t tap = .875
Ratings – have learnt contingencies
see notes
The Rescorla (1968) graph again.
This is evidence that rats can also track contingencies. As p(US|noCS) increases, the contingency,
p(US|CS) – p(US|noCS) decreases, and conditioning becomes less effective (higher suppression ratios).
see notes
timeline diagrams
see notes
significance of Pavlovian conditioning - then
A form of learning that could be described entirely objectively.
Provided a scientific underpinning for the concept of an association.
Contributed to the dominance of behaviorism in early twentieth century psychology; adopted as an account of all learning
significance of Pavlovian conditioning - now
Reliable, widespread phenomenon with determinable laws.
Practically useful, e.g. behavior therapy.
May account for involuntary, dysfunctional forms of human learning e.g. phobias.
Continued investigation of theories of Pavlovian conditioning (Rescorla-Wagner, Pearce-Hall, Dickinson, etc) – including some that are cognitive in nature, i.e. require animals to have mental representations of CS and UCS
It is not an explanation of all learning, but may give insight into fundamental learning processes. And these processes may well apply to humans.
human Pavlovian conditioning - case study
expectancy rating
SCR
Shown stimuli – paired with shock/light
autonomic conditioning
Note how over trials two things happen:
1) The participants expectancy of shock rises for S+ and drops for S-.
2) The change in skin conductance for S+ becomes larger than that for S-.
On this basis Lovibond and others have claimed that this is a form of Pavlovian conditioning in humans.
see notes
By separating out those participants who are aware of the contingencies (getting shocked to S+ not S-) from those who are not, it is possible to demonstrate that the effect is driven by the participants who have an expectancy of shock.
There is little evidence of conditioning in those who do not.
Hence, the claim that Pavlovian conditioning in humans requires a conscious cognitive expectancy of the US, and may not be the same as in other animals (e.g. the rat).
see notes
Hughdahl and Ohman (1977)
Further evidence in support of this view comes from the observation that if you now tell participants that no more shocks will occur - then the response quickly disappears (below left), in contrast to those tested in extinction (top left) but not given this information
see notes
If we use “fear relevant” stimuli (e.g. images of spiders and snakes) in this electrodermal conditioning paradigm then the results change.
There is now evidence that the responses are not entirely governed by conscious expectancy - and instead that there may be an automatic component that is more properly regarded as being due to Pavlovian conditioning.
see notes
McAndrew et al. (2012)
Given shocks – brown cylinder/pink square – 50% chance of shock
Rate expectancy of whether getting shock
Way respond depends on what recently experienced
A “run length” of -2, for example, means that we are looking at a trial following two non-reinforced (no shock)trials.
A run length of +2 would involve a trial following two reinforced (shock) trials.
Whether the current trial is reinforced or not does not come into consideration.
+1 = shock trial before
+2 = 2 shock trials before
-1 = no shock but brown cylinder – extinction
see notes
As no. Shock trial increase, expectancy of another one decreases – gamblers fallacy – but link between cylinder and shock incrwased
Expectancy not governing emotional reaction
see notes
