configural learning learning about holistic stimulus representations
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Configural learning Learning about holistic stimulus representations. no food. food. Structural discriminations George Ward-Robinson & Pearce, 2001. food. no food. Structural discriminations George Ward-Robinson & Pearce, 2001. Can this be solved in terms of simple associations? - PowerPoint PPT PresentationTRANSCRIPT
Configural learning
Learning about holistic stimulus representations
no food
food
food no food
Structural discriminationsGeorge Ward-Robinson & Pearce, 2001
Structural discriminationsGeorge Ward-Robinson & Pearce, 2001
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food no food
Can this be solved in terms of simple associations?
Can it be solved with conditional learning?
food no food
If green: red-left + red-right - If blue: red-left - red-right +If green: blue-right + blue-left -
food no food
If green: red-left + red-right - If blue: red-left - red-right +If green: blue-right + blue-left -
relies on use of compound cues - red-left etc
food no food
so why not use fact these stimuli are all unique?
red-left&green-right+ red-right&green-left -
Some types of learning associative theory cannot explain.
Last week we saw how conditional learning can explain some of these
Today we consider an alternative approach - configural learning
Can associative theory adapt by changing the way in which the stimulus is represented?
So far have assumed that a compound stimulus is equivalent to the sum of its parts:
A --> food B--> food
A --> crB --> cr
AB --> CR
Predict SUMMATION
Feature negative discrimination
A --> food AB --> no food
CR cr
VA = ( - V )
Learning stops when ( = V )
A --> food AB --> no food
VA = 1 VA + VB = 0
VA = ( - V )
Learning stops when ( = V )
A --> food AB --> no food
VA = 1 VA + VB = 0
A becomes excitatory: V = +1B becomes inhibitory: V = -1
thus A alone predicts food, whereas A+B is neutral
Feature positive discrimination
A --> no food AB --> food
cr CR
VA = ( - V )
Learning stops when ( = V )
A --> no food AB --> food
VA = 0 VA + VB = 1
VA = ( - V )
Learning stops when ( = V )
A --> no food AB --> food
VA = 0 VA + VB = 1
B becomes excitatory: V = +1A eventually becomes neutral: V = 0
Thus A alone predicts nothing, but when B is present food is expected
Performance on feature negative and feature positive discriminations can be explained by the Rescorla-Wagner equation
If you condition to asymptote, it predicts perfect performance
But how about.......
Positive patterning discrimination:
A --> no food B --> no food AB --> food
cr cr CR
VA = ( - V )
Learning stops when ( = V )
A --> no food B --> no food AB --> food
VA = 0 VB = 0 VA + VB = 1
A --> no food B --> no food AB --> food
VA = 0 VB = 0 VA + VB = 1
This one is insoluble - you can never reach asymptote:
what is gained on AB trials is lost on A and B trials
A --> no food B --> no food AB --> food
But associative theory can explain accurate performanceBoth A and B acquire associative strength on compound trials, and lose some on element trials
Animals respond more on AB trials (when two signals for food are present) than on A or B trials (when there is only one)
But it doesn't predict perfect performance
Negative patterning discrimination
A --> food B --> food AB --> no food
CR CR cr
VA = ( - V )
Learning stops when ( = V )
A --> food B --> food AB --> no food
VA = 1 VB = 1 VA + VB = 0
Simple associative theory can never predict accurate performance here
A --> food B --> food AB --> no food
If A and B have enough associative strength to elicit responding, then the compound of A and B must elicit more responding, not less
-- violates summation principle
So can animals learn nonlinear discriminations of this type?
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click + tone --> no food
tone --> foodclick --> food
Redrawn from Rescorla, 1972
Blocks of 60 Trials
Percentage responses
Wagner (1971) and Rescorla (1972) suggested the unique stimulus account:
A stimulus compound should be treated as the combination of its elements...
A B+
A stimulus compound should be treated as the combination of its elements... PLUS a further stimulus that is generated only when those elements are presented together:
A B
ab
+
A stimulus compound should be treated as the combination of its elements... PLUS a further stimulus that is generated only when those elements are presented together:
A B
ab
+configural stimulus notvery salient; so only learned about when absolutely "forced"
Now the negative patterning discrimination looks like this:
A --> food B --> food AB --> no food
Now the negative patterning discrimination looks like this:
A --> food B --> food AB ab --> no food
Now the negative patterning discrimination looks like this:
A --> food B --> food AB ab --> no food
VA = 1 VB = 1 VA + VB+ Vab = 0
A --> food B --> food AB ab --> no food
VA = 1 VB = 1 VA + VB+ Vab = 0
B becomes excitatory: V = +1A becomes excitatory: V = +1ab becomes inhibitory: V = -2
...and the discrimination is solved...
Rescorla tested this interpretation with the following experiment:
A + B + AB - AB + A ? B ?
A + B + C - AB + A ? B ?
Which group will respond more in the test?
Stage 1 Stage 2 Test
A + B + AB ab - AB ab + A ? B ?
Stage 1 Stage 2 Test
A + B + AB ab - AB ab + A ? B ?
In Stage 1 A and B become excitatory and ab inhibitory; the combination of A, B and ab should therefore be neutral
Stage 1 Stage 2 Test
A + B + AB ab - AB ab + A ? B ?
In Stage 1 A and B become excitatory and ab inhibitory; the combination of A, B and ab should therefore be neutral
In Stage 2 the neutral AB ab is paired with food; the food is surprising, and A, B and ab all gain associative strength
Stage 1 Stage 2 Test
A + B + AB ab - AB ab + A ? B ?
In Stage 1 A and B become excitatory and ab inhibitory; the combination of A, B and ab should therefore be neutral
In Stage 2 the neutral AB ab is paired with food; the food is surprising, and A, B and ab all gain associative strength
In the Test A and B now have more associative strength than they started with
Stage 1 Stage 2 Test
A + B + C - AB + A ? B ?
Stage 1 Stage 2 Test
A + B + C - AB + A ? B ?
In Stage 1 A and B become excitatory
Stage 1 Stage 2 Test
A + B + C - AB + A ? B ?
In Stage 1 A and B become excitatory
In Stage 2 the excitatory A and B both predict food -- thus two foods are predicted, but only one happens; this produces inhibitory learning, and the strength of A and B drops...
Stage 1 Stage 2 Test
A + B + C - AB + A ? B ?
In Stage 1 A and B become excitatory.
In Stage 2 the excitatory A and B both predict food -- thus two foods are predicted, but only one happens; this produces inhibitory learning, and the strength of A and B drops...
In the Test A and B now have less associative strength than they started with
Responding to A and B
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Group C-Group C-
Group AB-Group AB-
Redrawn from Rescorla 1973
Blocks of 10 trials
Mean percentage responses
So.. can Rescorla & Wagner explain everything?
Not quite: consider the following discriminations:
Discrimination 1: A+ AB-
Discrimination 2: AC+ ABC-
In the second case a common element C has been added on both reinforced and nonreinforced trials; this should make the discrimination harder...
So.. can Rescorla & Wagner explain everything?
Not quite: consider the following discriminations:
Discrimination 1: A+ AB-
Discrimination 2: AC+ ABC-
In the second case a common element C has been added on both reinforced and nonreinforced trials; this should make the discrimination harder...
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A +
AC+ABC-
AB-
Redrawn from Pearce 1994
Session
Responses per minute
BUT Rescorla & Wagner's theory predicts that the AC+ ABC- discrimination will be learned most easily
Because AC has more elements than A, it will acquire associative strength faster
Discrimination 1: A+ AB-
Discrimination 2: AC+ ABC-
BUT Rescorla & Wagner's theory predicts that the AC+ ABC- discrimination will be learned most easily
Because AC has more elements than A, it will acquire associative strength faster
Discrimination 1: A+ AB-
Discrimination 2: AC+ ABC-
on first trial VA = ( - V ) = ( - 0 )
Vc = ( - V ) = ( - 0 )
So AC will have twice as much strength as A after trial 1
Faster EXCITATORY learning
Discrimination 1: A+ AB-
Discrimination 2: AC+ ABC-
And the more AC predicts food, the greater the surprise on ABC- trials, and so the faster B will become inhibitory
Faster INHIBITORY learning
Discrimination 1: A+ AB-
Discrimination 2: AC+ ABC-
The faster the excitatory and inhibitory learning is acquired, the faster the discrimination is acquired
oops!
Nor can Rescorla & Wagner's theory explain any instance of generalization decrement
e.g. external inhibition (Pavlov, 1927)
control A+ test A CR=10
A+ test AB CR=5
the presence of B makes the animals respond less to A
yet if associative strengths summate, as Rescorla and Wagner predict, then if A = 1 and B = 0, then AB = A = 1
Pearce's theory of stimulus generalization (1987; 1994)
Limited capacity buffer representing overall pattern of stimulation that is present
Every stimulus is a
configure
and
unique
tone
context
context
Pearce's theory of stimulus generalization (1987; 1994)
a compound stimulus isNOT the sum of itselements
so you need a way of working out how much learning about one stimulus will affect responding to another
tone
context
context
Changing the stimulus in any way changes the contents of the buffer
you work out how similarthey are, and use that tocalculate how muchgeneralisation occurs
tone
context
context
clicker
context
context
Compound stimuli are unique -- NOT the sum of theirelements
or are they..?!
Despite claim that elementsnot represented, they areused to calculatesimilarity betweenconfigurations
tone
context
context
Generalization between two stimuli depends on :
(i) their similarity (number of common elements)(ii) the amount of associative strength tone and clicker have common and unique elements(ignore context for simplicity)
clickerunique
comm
n
comm
on
tone unique
comm
on
comm
on
TONE CLICKER
Suppose you condition a tone to asymptote (i.e. V=1) and then test the generalization to a click.
Let 50% of the buffer contents in each case be common elements
clickerunique
comm
n
comm
on
toneunique
comm
on
comm
on
Generalization = (V tone) x click/tone similarity
clickerunique
comm
n
comm
on
toneunique
comm
on
comm
on
Generalization = (V tone) x click/tone similarity
Click/tone similarity = Pcom/Ptone total x Pcom/Pclick total
i.e. common/source x common/target
clickerunique
comm
n
comm
on
toneunique
comm
on
comm
on
Generalization = (V tone) x click/tone similarity
Click/tone similarity = Pcom/Ptone total x Pcom/Pclick total
= 50% x 50%
= 25%
clickerunique
comm
n
comm
on
toneunique
comm
on
comm
on
Need to ask --
(i) associative strength of thing being generalised from?
clickerunique
comm
n
comm
on
toneunique
comm
on
comm
on
Need to ask --
(i) associative strength of thing being generalised from?(ii) what are the common elements mediating generalisation?
clickerunique
comm
n
comm
on
toneunique
comm
on
comm
on
Need to ask --
(i) associative strength of thing being generalised from?(ii) what are the common elements mediating generalisation?(iii) what % are common elements of stimulus generalised
from?
clickerunique
comm
n
comm
on
toneunique
comm
on
comm
on
Need to ask --
(i) associative strength of thing being generalised from?(ii) what are the common elements mediating generalisation?(iii) what % are common elements of stimulus generalised
from?(iv) what % are common elements of stimulus generalised to?
clickerunique
comm
n
comm
on
toneunique
comm
on
comm
on
Suppose you condition a tone+light compound to asymptote (V = +1) and then test generalization to the tone:
TL+ test T
tonetone
light
light
Suppose you condition a tone+light compound to asymptote (V = +1) and then test generalization to the tone:
TL+ test T
Let tone and light share no intrinsic common elementsSo the relevant common elements are those of the tone tone/light equally salient so tone 50% of total
tonetone
light
light
Generalization = (V tone+light) x (tone+light)/tone similarity
tonetone
light
light
Generalization = (V tone+light) x (tone+light)/tone similarity
= P tone/Ptone+light total x Ptone / Ptone total
= 50% x 100%
= 50%
tonetone
light
light
work out generalization in the following cases (V = +1):
(i) condition tone; test (tone+light)
i.e. A+ AB?
(ii) condition tone; test (tone+light+clicker)
i.e. A+ ABC?
(iii) condition (tone+light); test (clicker+light)
i.e. AB+ AC?
work out generalization in the following cases (V = +1):
(i) condition tone; test (tone+light)
i.e. A+ AB? A/A x A/AB = 1/2
(ii) condition tone; test (tone+light+clicker)
i.e. A+ ABC?
(iii) condition (tone+light); test (clicker+light)
i.e. AB+ AC?
work out generalization in the following cases (V = +1):
(i) condition tone; test (tone+light)
i.e. A+ AB? A/A x A/AB = 1/2
(ii) condition tone; test (tone+light+clicker)
i.e. A+ ABC? A/A x A/ABC = 1/3
• condition (tone+light); test (clicker+light)
i.e. AB+ AC?
work out generalization in the following cases (V = +1):
(i) condition tone; test (tone+light)
i.e. A+ AB? A/A x A/AB = 1/2
(ii) condition tone; test (tone+light+clicker)
i.e. A+ ABC? A/A x A/ABC = 1/3
• condition (tone+light); test (clicker+light)
i.e. AB+ AC? A/AB x A/AC = 1/4
There is also a little complication with V....
Compare with Rescorla Wagner equation for one stimulus:
V = ( - V )
Pearce uses this equation for acquisition of V:
V = ( - (V + g))
Adds together acquired strength (V) and generalised strength (g)
generalized associative strength acts like normal associative strength during acquisition
V = ( - (V + g))
generalized associative strength acts like normal associative strength during acquisition
V = ( - (V + g))
but it doesn't generalise!!
To see why this is important, let's look at overshadowing and blocking:
light + light? CR = 10
tone+light + light? CR = 5
tone+ tone+light + light? CR = 2
Control light + light ?
light acquires strength in training V = +1
in test responding determined by generalization
P light/Plight x Plight / Plight = 1
lightlight
overshadowing tone&light + light ?
tone&light configure acquires strength in training V = +1
in test responding determined by generalization
P light/Ptone+light x Plight / Plight = 1/2
tonelight
light light
blockingtone + tone&light + light ?
in Stage 1 tone acquires strength in training V = +1
tone
blocking tone + tone&light + light ?
in Stage 2 learning about tone generalises to tone/light :
P tone/Ptone x Ptone / Ptone+light = 1/2
tone tone
light
light
blocking tone + tone&light + light ?
So tone/light starts halfway to asymptote because of generalisation
Vtone+light = ( - (Vtone+light + gtone+light))
= ( - (0 + 1/2))
tone tone
light
light
blocking tone + tone&light + light ?
So tone/light starts halfway to asymptote because of generalisation
Half of its total associative strength will be generalised, and only half will be acquired
tone tone
light
light
blockingtone + tone&light + light ?
So tone/light starts halfway to asymptote because of generalisation
Half of its total associative strength will be generalised, and only half will be acquired
Only the acquired half can generalise to other stimuli
tone tone
light
light
blockingtone + tone&light + light ?
test responding determined by generalization to tone of 1/2 of what is acquired by tone/light: ( P light/Ptone+light x Plight / Plight = 1/2 ) x 1/2 = 1/4
lighttone
light
light
Pearce's model can explain things that the unique cue (Rescorla & Wagner) cannot
But it's a paradox: it rejects the idea of stimulus elements, and yet it uses them all the time
Brandon Vogel and Wagner (2000) analysed Pearce's model in terms of stimulus elements
They argued that the best way of thinking about Pearce's model is in terms of removed elements
Imagine you have two stimuli, A and B:
If you present them in compound, which elements are active?
A B
Simple model
AB compound
A B
Rescorla and Wagner's account:added elements
AB compound
ab
A B
Pearce's account:removed elements (remember buffer is limited capacity)
AB compound
A B
So can these models explain external inhibition?
Simple model
A+ test AB
A
B
A
So can these models explain external inhibition?
Rescorla Wagner added elements model
A+ test AB
A
B
A
ab
So can these models explain external inhibition?
Pearce's removed elements model
A+ test AB
A
B
A
Can removed elements explain other Pearce predictions?
condition tone; test tone+light+clicker
i.e. A+ ABC? A/A x A/ABC = 1/3
A
B
A
C
Can removed elements explain other Pearce predictions?
condition tone+light; test clicker+light
i.e. AB+ AC? A/AB x A/AC = 1/4
A
B C
A
Can removed elements explain other Pearce predictions?
condition tone+light; test clicker+light
i.e. AB+ AC? A/AB x A/AC = 1/4
A
B C
A
A connectionist version of the unique cue view?
foodfood no food
A connectionist version of the unique cue view?
food no food
left right
configural units
A connectionist version of the unique cue view?
food no food
left right
configural units
A connectionist version of the unique cue view?
food no food
left right
configural units
A connectionist version of the unique cue view?
food no food
left right
configural units
Finally - configural cues versus conditional learning
Many of the tasks we have considered today could be solved in terms of conditional learning
e.g. A --> food B --> food AB --> no food
A signals that B is nonreinforced (or vice versa)
but others not so easily:
So which is right?
Configural learning very probably does occur
the question is whether it is enough to explain all data - or do we need a theory of conditional learning too...
the experiments I presented at the end of my last lecture were designed to examine this question...
quite possible that some tasks better solved by a conditional learning mechanism
References
Brandon, S.E., Vogel, A.H., & Wagner, A.R. (2000). A componential view of configural cues in generalization and discrimination in Pavlovian conditioning. Behavioral Processes, 110, 67-72. *
George, D., Ward-Robinson, J., & Pearce, J.M. (2001). Discrimination of structure I: Implications for connectionist theories of discrimination learning. Journal of Experimental Psychology: Animal Behavior Processes, 27, 206-218.
Pearce, J.M. (1987). A model for stimulus generalization in Pavlovian conditioning. Psychological Review, 94, 61-73. *
Pearce, J.M. (1994). Similarity and discrimination: A selective review and a connectionist model. Psychological Review, 101, 587-607.
Rescorla, R.A. (1973). "Configural" conditioning in discrete-trial bar pressing. Journal of Comparative and Physiological Psychology, 79, 301-317. *
Rescorla, R.A. (1972). Evidence for "Unique stimulus" account of configural conditioning. Journal of Comparative and Physiological Psychology, 85, 331-338. *
Wagner, A.R. (1971). Elementary associations. In H.H. Kendler & J.T. Spence (Eds.) Essays in neobehaviorism: A memorial volume to Kenneth W. Spence. New York: Appleton-Century-Crofts.