Effects of stimulus preexposure. Stimulus preexposure affects our ability to perceive and discriminate stimuli: Stimulus recognition memory – in humans

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


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


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

atio

Day 1 Day 8 Test

rats responding for food;novel stimulus suppresses this responding

low ratio--> high suppression

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Same

Different


up

pre

ssio

n R

atio

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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14

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C o lu m n 1

Data from Hoffeld 1962 (Redrawn from Hall 1991)

Level of training %

Mea

n n

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


up

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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

io

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

4321010

20

30

40

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

4

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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:


AX AX --> LiCl BX ?

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


AX AX --> LiCl BX ?

BX AX --> LiCl BX ?


In Group W X is novel and conditions well – BX very nasty


AX AX --> LiCl BX ?

BX AX --> LiCl BX ?



In Group AX X is latently inhibited and conditions less well – BX less nasty


AX AX --> LiCl BX ?

BX AX --> LiCl BX ?



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


AX AX --> LiCl BX ?

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:


AX AX AX AX BX BX BX BX AX --> LiCl BX ?

AX BX AX BX AX BX AX BX AX --> LiCl BX ?

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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:




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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


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?



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Amount Drunk (ml)

IntermixedBlocked



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

Documents

Effects of stimulus preexposure. Stimulus preexposure affects our ability to perceive and discriminate stimuli: Stimulus recognition memory – in humans