effects of stimulus preexposure. stimulus preexposure affects our ability to perceive and...
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Effects of stimulus preexposure
Stimulus preexposure affects our ability to perceive and discriminate stimuli:
Stimulus recognition memory – in humans can be by report- in animals indexed by spontanous object recognition task
A A A B
if recognise A will explore B more (A is
boring)Ennaceur & Delacour 1988
Aim was to develop a memory task parallel to those used in humans
for e.g. studying amnesia
Perceptual learning -- improves discrimination between stimuli
How do these effects work? We need to understand exactly what stimulus exposure does
Gibson & Gibson (1955) proposed: "percepts change over time by progressive elaboration of qualities, features and dimensions of variation"
They assumed that effects of stimulus exposure are not associative - but no formal mechanism was proposed
Were they right?
Or are these phenomena the result of associative processes?
In lecture we will ask what are possible explanations of
1 object recognition?
2 perceptual learning?
in doing so we will talk about what the general associative model says are the effects of stimulus preexposure
According to the associative model, stimulus preexposure can have several effects on
behaviour:
1 it can reduce responding – habituation
this will help us understand recognition memory
- relevance to human amnesia
According to the associative model, stimulus preexposure can have several effects on
behaviour:
2 it can reduce learning -- latent inhibition
this will help us understand those conditions in which learning is aberrant or harmful
- schizophrenia- chemotherapy ANV- phobias- drug tolerance effects
According to the associative model, stimulus preexposure can have several effects on
behaviour:
3 it can produce learning among elements of the stimulus – within-compound associations
helps us understand how we learn about complex events
Stimulus object recognition
This seems very similar to habituation task:
A? large UCR
A A A A A? small UCR
A A A B
Three theories of habituation
Fall within general associative model:
Wagner's theory
S-R theory
Nonassociative (maybe!) -- Comparator theory
Wagner's theory
Short term habituation
After many trials CS elements in A2 --> reduced response
I A1
A2
I A1
A2
Wagner's theory
Long term habituation
Context becomes associated with CS.
Sends CS elements into A2 --> reduced response
context
I A1
A2
I A1
A2
How can we test Wagner's theory?
predicts unconditioned response will return in a different context
Honey and Hall (1989) investigated this:
habituated stimulus in one context, test same or different context
Train
tone
Test
Same tone ucr
Different tone UCR
what is wrongwith thisdesign?
Train
tone
Test
Same tone
Different tone
Train
tone click
Test
Same tone
Different tone
Train
tone click
Test
Same tone click
Different tone click
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Same
Different
Data redrawn from Hall & Honey, 1989S
up
pre
ssio
n R
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Day 1 Day 8 Test
rats responding for food;novel stimulus suppresses this responding
low ratio--> high suppression
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Same
Different
Data redrawn from Hall & Honey, 1989S
up
pre
ssio
n R
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Day 1 Day 8 Test
rats responding for food;novel stimulus suppresses this responding
low ratio--> high suppression
This interpretation of Wagner's theory fails in explaining simple habituation...
how about other theories?
S-R theory and comparator theory say nothing about context...
S-R theory
Link between S and R becomes less effective with use
UR
UR
Comparator theory
Stimulus compared with internal representation. Novel stimulus has no internal representation, so strong UCR is elicited
Mismatch!
Large UR
Comparator theory
...but preexposure gradually allows a mental representation of the stimulus to be established:
Partial mismatch!
Smaller UR
Comparator theory
until detailed stimulus representation is formed
Match!
small UR
Which is right? The stimulus omission effect
Train with a compound stimulus
Test with all or part
?
?
S-R theory says.....
UR UR UR UR
UR
Habituation maintained
Comparator theory says.....
Habituation abolished
Mismatch!
Mismatch!
Match!
Habituation is abolished (see Hall 91)... but is it good evidence for comparator theory? Or could S-R theory explain it…?
UR UR UR UR
UR
aftereffects of tone are like anovel stimulus
UR
Other evidence for comparator theory
Extended exposure increases detail in stored representation
After short training.... After extended training
Other evidence for comparator theory
test stimulus
Hard to discriminate Easy to discriminate
Stimulus now easier to discriminate from other, similar stimuli
*
*
*
*
predicts extended training will reduce generalisation:
A+ CR
A+ A+ A+ A+ A+ A+ cr
predict less generalised responding to B after more training
(usually more training
--> more generalisation as more responding to A)
A B
50 95 190 285543210
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C o lu m n 1
Data from Hoffeld 1962 (Redrawn from Hall 1991)
Level of training %
Mea
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um
ber
of
test
res
po
nse
s
Responding to B
Training of A -->
Hoffeld 1962 cited in Hall 91
Problem: comparator theory has no mechanism.
…. and is it necessarily nonassociative?
McLaren & Mackintosh 2000 proposed several associative mechanisms arising from stimulus preexposure that could produce such effects
unitisation (sticking units together)
this idea is actually very similar to Wagner’s model...
when elements are linked they send each other into A2, explaining habituation
temporal B relatively novel
spatial A’ and B’ in unfamiliar place
B B A BA A
A B
A’ B’
A B
B’ A’
can this theoryexplain thesestimulus recognition effects?
from Good Barnes Staal McGregor & Honey 2007
Train
Test
A A
A B
B B
A A
A B
A B
A’ B’
A B
B’ A’
can this theoryexplain thesestimulus recognition effects?
Before Perceptual Learning --Latent inhibition (LI)
Preexposing a stimulus reduces learning about it. Can’t really talk about effects of stimulus preexposure without talking about latent inhibition
LI important for a number of practical reasons
faulty latent inhibition indicated in schizophrenia
relevant to preventing anticipatory nausea and vomiting
relevant to phobias, drug addiction – determines what is learned about
Theories of Latent Inhibition
1 Wagner's theory: CS predictability
2 CS predictive ability (Pearce &Hall 1980, Mackintosh 1975)
3 Retrieval failure
Wagner's account: CS predictability
context context context context
CS CS CS CS+
If CS preexposed, association forms between context and CS
Now context puts most CS elements into A2
CS can't easily recruit elements into A1 poor learning
Theory predicts that latent inhibition will be context specific
Honey and Hall 1989 – context specificity of habituation – went on to look at latent inhibition in same experiment:
TRAIN
tone click
TEST
Same tone click
Different tone click
TRAIN
tone click
TEST
Same tone+ click+
Different tone+ click+
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Same
Different
Data redrawn from Hall & Honey, 1989S
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Day 1 Day 8 Test Conditioning
Wagner's account also predicts that extinguishing the context should reduce latent inhibition, because this will weaken the context-->CS association:
click
click
click+ SLOW
click+ FAST
Baker and Mercier (1982) tested effect of context extinction:
Group no pre click+ FAST
Group pre click click+ slow
Group pre/ext click click+ FAST
group pre should show latent inhibition, but group pre/ext should not
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Group pre
Group pre/ext
Group no pre
Data redrawn from Baker and Mercier Experiment 1
Days
Su
pp
ress
ion
rat
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predictability of CS does not determine latent inhibition
....so Wagner's theory not completely right
can you think of another wayWagner can explain latent inhibition?
CS predictive ability theories
V = ( - V)
refers to associability of a stimulus. Rescorla & Wagner assumed that this was a fixed property of a stimulus
But Mackintosh (1975) suggested that might change with experience --
good predictors command attention
Mackintosh 1975
VA = ( - VA)
A >0 if I - VAI < I - VxI
if CS is better at predicting the outcome than anything else, then its goes UP
A <0 if I - VAI >= I - VxI
if CS is no better at predicting the outcome than anything else, then its goes
DOWN
Unique evidence for this comes from intradimensional/extradimensional shift tasks
+
+
Train colour relevant (shape irrelevant)
then test on a new task with different stimuli
+
+
+
+Test colour relevant (shape irrelevant)
+
++
+
+
+Test colour relevant (shape irrelevant)
or shape relevant (colour irrelevant)
If colour stays relevant, test is easier.
Theory is that attention to predictive colour dimension has increased, whereas attention to nonpredictive shape dimension has decreased
(e.g. Mackintosh & Little, 1969)
but not all the evidence is that good....
Pearce & Hall, 1980
Pearce and Hall (1980) also suggested that might change with experience –
but they predict the opposite
bad predictors command attention
A novel stimulus has high because its outcome is uncertain
but if stimulus is preexposed -- latent inhibition -- drops because CS is a good predictor of nothing
Pearce & Hall, 1980
... if a stimulus is conditioned and the outcome always occurs -- drops
CS+ CS+ CS+ CS+
this is because CS is a good predictor of something
... but if a stimulus is conditioned and the outcome only occurs occasionally -- stays high
CS+ CS- CS+ CS-
this is because CS is an unreliable predictor
Pearce & Hall, 1980
V = S
n = In-1 - Vn-1I
suggested that related to the orienting response (OR)
uncertain outcome -- High -- lots of orienting
certain outcome -- low -- little orienting
Swan & Pearce manipulated the predictive ability of a light CS to be higher in Group Same than in Group Different:
Group Same
Group Different
tone
click
light
light
food
food
tone
click
light
light
food
food
tone
click
light
light
food
food
Predict:
Group Same: light has (relatively) predictable outcomes
low -- little orienting and learned about slowly....
Group Different: light had unpredictable outcomes
high -- high orienting and learned about fast....
-- tested orienting to light
-- paired light with food to look at learning speed
light food
2010010
20
30
40
50
60
Group Different
Group Same
Redrawn from Swan & Pearce 1988
Sessions
Per
cen
t O
bse
rvat
ion
s
More orienting to light inGroup Different
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20
30
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50
60
Group Different
Group Same
Redrawn from Swan & Pearce 1988
Sessions
Mag
azin
e ac
tivi
ty
More conditioned respondingto light in Group Different
One final theory
Some have argued that learning is normal after latent inhibition, but that retrieval is impaired
Two associations CS--> nothing (from preexposure)
CS--> US (from conditioning)
two associations compete, and so less CR
Not much evidence for this but you should know it's a possibility
Latent inhibition summary 1
Mixed support for Wagner's account – whether CS is predicted matters
context extinction doesn’t eliminate latent inhibition
but it is context specific
could we adapt Wagner’s theory but say elements of the stimulus becoming associated with each other cause LI, not just associations with the context?
Latent inhibition summary 2
Mackintosh and Pearce Hall – whether CS is predictive matters
Mackintosh says predictive stimuli command attention:
evidence -- intradimensional/extradimensional shifts
Pearce & Hall say predictive stimuli ignored:
evidence -- expected effects on orienting and on conditionability
see Le Pelley (2004) for discussion of paradox...
evidence for Pearce-Hall comes from studies with one CS
evidence for Mackintosh looks at stimuli in compounds...
Perceptual Learning
Gibson & Walk (1956) exposed animals to stimuli in their home cages
Then tested them to discriminate between the stimuli in a jumping stand
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Early Control
Late Control
Early Experimental
Late Experimental
Gibson & Walk (1956) (redrawn from Hall 1991)
5-Day Blocks
Err
ors
Standard procedure
AX --> LiCl BX ? 5ml (low)
Rats are conditioned to a compound flavour AX, and then tested with a similar flavour BX (A and B are sucrose and saline, X is lemon)
Distinguish between the common elements (X)and the unique elements (A and B)
Animals reject BX because the common element X was paired with LiCl
preexpose condition test
water AX --> LiCl BX ?
AX AX --> LiCl BX ?
BX AX --> LiCl BX ?
AX BX AX --> LiCl BX ?
preexposing both stimuliseems to help discrimination
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1
Amount drunk (ml)
W
AX
BX
AX/BX Redrawn from
Symonds & Hall1995
What’s the explanation? Clue is in common elements:
water AX --> LiCl BX ?
AX AX --> LiCl BX ?
BX AX --> LiCl BX ?
AX BX AX --> LiCl BX ?
remember animals reject BX because the common element X was paired with LiCl
so the less X conditions the less animals reject BX
water AX --> LiCl BX ?
AX AX --> LiCl BX ?
BX AX --> LiCl BX ?
AX BX AX --> LiCl BX ?
In Group W X is novel and conditions well – BX very nasty
water AX --> LiCl BX ?
AX AX --> LiCl BX ?
BX AX --> LiCl BX ?
AX BX AX --> LiCl BX ?
In Group W X is novel and conditions well – BX very nasty
In Group AX X is latently inhibited and conditions less well – BX less nasty
water AX --> LiCl BX ?
AX AX --> LiCl BX ?
BX AX --> LiCl BX ?
AX BX AX --> LiCl BX ?
In Group W X is novel and conditions well – BX very nasty
In Group AX X is latently inhibited and conditions less well – BX less nasty
In Group BX X is latently inhibited and conditions less well – BX less nasty
water AX --> LiCl BX ?
AX AX --> LiCl BX ?
BX AX --> LiCl BX ?
AX BX AX --> LiCl BX ?
In Group AX/BX X elements are exposed twice as much as in Group AX or BX
-- so conditions twice as badly – BX not very nasty at all
Latent inhibition of common elements is one mechanism of perceptual learning - McLaren & Mackintosh 2000
... but it is not all:
preexpose condition test
AX AX AX AX BX BX BX BX AX --> LiCl BX ?
AX BX AX BX AX BX AX BX AX --> LiCl BX ?
0
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1
Amount Drunk (ml)
IntermixedBlocked Redrawn from
Symonds & Hall1995
Intermixed and blocked schedules of exposure to AX and BX should produce identical latent inhibition to X
... but it is not all: what about this experiment:
preexpose condition test
AX AX AX AX BX BX BX BX AX --> LiCl BX ?
AX BX AX BX AX BX AX BX AX --> LiCl BX ?
0
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1
Amount Drunk (ml)
IntermixedBlocked
so what is going on?!
Learning about elements of a stimulus
McLaren & Mackintosh 2000 proposed several associative mechanisms arising from stimulus preexposure that involve learning about elements of a stimulus, and that could produce perceptual learning
1 unitisation (sticking units together) – see above
2 latent inhibition of common elements
3 mutual inhibition between unique elements
AX BX AX --> LiCl BX ?
Rats fear BX because X has been conditioned… but there is another reason:
-- X is associated with A, which has also been conditioned
… so if you can stop X making the animals think of A, they will drink more BX
A
LiClBX
Intermixed preexposure could stop X making you think of A…
Remember conditioned inhibition...
tone --> food tone+light --> nothing
makes light an inhibitor for food, because tone makes you think about food which doesn't happen...
food
this could happen in AX and BX preexposure:
X A B X
X B A X
A
B
on BX trialsX makes youthink of A, butno A happens..;so B comesto inhibit A
same on AXtrials
this could happen in AX and BX preexposure:
X A B X
X B A X
... so B becomes an inhibitor of A (and vice versa)
A
B
Mutual Inhibition of Unique Elements
So now when tested with BX, even though X tries to make you think of A…
A
LiClBX
Mutual Inhibition of Unique Elements
So now when tested with BX, even though X tries to make you think of A…
… B will stop you thinking of A,
which stops you thinking of LiCl
A
LiClBX
So how does all this help explain this result?
AX AX AX AX BX BX BX BX AX --> LiCl BX ?
AX BX AX BX AX BX AX BX AX --> LiCl BX ?
0
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Amount Drunk (ml)
IntermixedBlocked
AX AX AX AX BX BX BX BX AX --> LiCl BX ?
AX BX AX BX AX BX AX BX AX --> LiCl BX ?
A A A A
AAA A
This mechanism requires a strong XA association... and the association is weaker in the blocked case
Perceptual learning summary
Several types of learning could result from stimulus exposure, that could contribute to perceptual learning
Unitisation (see habituation)
Latent inhibition of common elements
Mutual inhibition of unique elements
So is there any no associative component, as the Gibsons proposed? No one has found one yet...
References
Baker, A.G., & Mercier, P. (1982). Extinction of the context and latent inhibition. Learning and Motivation, 13, 391-416.
Dickinson (1980) Contemporary associative learning theory. Cambridge University Press. Ch. 4 discusses Pearce & Hall and Mackintosh models mathematically
Ennaceur, A., & Delacour, J., (1988). A newone-trial test for neurobiological studies of memory in rats 1: Behavioral data. Behavioural Brain Research, 31, 47-59. Object recognition task
Gibson, E.J., & Walk, R.D. (1956). The effect of prolonged preexposure to visually presented patterns on learning to discriminate them. Journal of Comparative and Physiological Psychology, 49, 239-242.
Good, M.A., Barnes, P., Staal, V., McGregor, A., & Honey, R.C. (2007). Context- but not familiarity-dependent forms of object recognition are impaired following excitotoxic hippocampal lesions in rats. Behavioural Neuroscience, 121, 218-223. Talks about object recognition from an associative perspective
Hall, G. (1991) Perceptual and Associative learning. Oxford University Press. Chapters on habituation, latent inhibition and perceptual learning
Hall, G., & Honey. R.C. (1989). Contextual effects in conditioning, latent inhibition and habituation: Associative and retrieval functions of contextual cues. Journal of Experimental Psychology: Animal Behavior Processes, 15, 232-241. Discusses Wagner’s acount of habituation and latent inhibition
References
Hoffield, D.R. (1962). Primary stimulus generalisation and secondary extinction as a function of strength of conditioning. Journal of Comparative and Physiological Psychology, 55, 27-31.
Le Pelley, M.E. (2004). The role of associative history in models of associative learning: A selective review and a hybrid model. Quarterly Journal of Experimental Psychology, 57B, 193-243. discusses discrepancy between Pearce Hall and Mackintosh theories
McLaren, I.P.L., & Mackintosh, N.J. (2000). An elemental model of associative learning: 1. Latent inhibition and perceptual learning. Animal Learning and Behavior, 26, 211-246. (be selective, it's quite dense; they obviously like their theory)
Mackintosh, N.J. (1975). A theory of attention: variation in the associability of stimuli with reinforcement. Psychological Review, 82, 276-298.
Mackintosh, N.J., & Little, L. (1969). Intradimensional and extradimensional shift learning by pigeons. Psychonomic Science, 14, 5-6.
Pearce, J.M., & Hall, G. (1980). A model for Pavlovian learning: Variations in the effectiveness of conditioned but not of unconditioned stimuli. Psychological Review, 87, 532-552.
Swan, J.A., & Pearce, J.M. (1988). The orienting response as an index of stimulus associability in rats. Journal of Experimental Psychology: Animal Behavior Processes, 14, 292-301.
Symonds, M., & Hall, G. (1995). Perceptual learning in flavor aversion conditioning: Roles of stimulus comparison and latent inhibition of common elements. Learning and Motivation, 26, 203-219. Discusses several associative mechanisms of perceptual learning