Generalization, Discrimination, and Stimulus Control
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Variability
 Changing conditions
 Adaptive learning must adapt
 Transfer behaviour across situations
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Generalization
 Tendency for a learned behaviour to occur in the
presence of stimuli not present during training
 e.g. Little Albert  conditioned fear to white rat, also
afraid of terrier, santa mask, fur coat
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Discrimination
 Tendency for a learned behaviour to occur in the
presence of certain stimuli, but not in their absence
 Inversely related to generalization
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Stimulus Control
 Stimuli come to exert influence over behaviour
 Application of generalization and discrimination
 CS+ and CS-
 S+ and S S+ indicates more reinforcing outcome, S- less
reinforcing (or even aversive) outcome
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Discrimination Training
 Any procedure that establishes the ability to
discriminate between stimuli
 Process by which stimulus control is established
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Generalization
 Not a given
 Can increase generalization by training in a variety of
settings
 Generalization not always appropriate or useful (e.g.,
generalizing violence from video game to real world)
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Generalization Gradients
 Measure of generalization/discrimination
 Respond to stimuli more like trained stimuli
 Train on one stimulus, test on others
 Techniques/methodologies
Amount of
responding
Train with
yellow
stimulus
Test with
all colours
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Probe Trials
 Insert occasional unreinforced test stimulus
training stimulus
(reinforced)
trials
probe stimulus
(unreinforced)
 Won’t extinguish since there are still many reinforced
trials
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Extinction Blocks
 Train stimulus to asymptote
 Blocks of extinction trials
 Each stimulus presented once/block
 Extinction constant across stimuli
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# of responses
4+3+1 = 8
Extinction
Blocks
20+15+10 = 45
15+11+5 = 30
12+7+3 = 22
3+1+0 = 4
Training
Block 1
Generalization Gradient
4 20 15 12 3
50
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3 1 15 11
Block 3
0 5 10 1 3
and so on...
Responses
Block 2
40
30
20
10
Light wavelengths
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Stim. continuum
Flat:
No discrimination
Response rate
Response rate
Response rate
Reading a Generalization Gradient
Stim. continuum
Broad:
Some discrimination
Stim. continuum
Narrow:
Lot of discrimination
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Semantic Generalization
 Doesn’t have to be a perceptual stimuli
 Generalization of abstract feature
 Adults ate candy (US) to salivate (UR) while shown
words (style, urn, freeze, surf)
 Shown homophones (stile, earn, frieze, serf)
 Shown synonyms (fashion, vase, chill, wave)
 CRs for homophones, but very strong CRs for
synonyms
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Generalization Post Extinction
 Classical or Operant training, then extinction
 Produces reduction in generalization to other stimuli
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Generalization of Punishment
 Suppression of behaviour via punishment also
generalizes
 Honig & Slivka (1964)
Number of
 Pigeons peck coloured disk, get reinforced (7 colours)
Responses
 Next, peck green disk, get shocked
 Gradient forms
 Greatest reduction of pecking to “greener” colours
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Presence/Absence Training
 Successive Discrimination Training
 Go-No Go procedure (operant)

Sometimes, reinforced for “no go”
 S+ & S- alternate randomly (S+ --> reinf., S- -->
extintion)
 Simultaneous Discrimination Training
 S+ & S- presented at same time
Peck
Don’t Peck
Peck (GO)
Don’t
(No Go)
Peck
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 Matching to Sample (MTS)
 Select from 2+ alternatives
(comparison stimuli) the
stimulus that is the same
as the sample
 Mismatching (non-
Delayed
Non-match
MTSMTS
matching to sample)
 Like MTS, but pick
comparison stimulus not
like sample
 Delayed Matching to
Don’t
Peck
Peck
Sample (DMTS)
 Like MTS, but delay
between presentation of
sample and choice
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Errorless Discrimination Training
 Previous techniques slow
 Many mistakes where S- selected
 Present S+ as normal, but start S- at low salience
(short time and “faint”)
 Gradually increase salience of S- to equal S+
 Quick, relatively little frustration for S- choice, greater
discrimination learned
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Differential Outcomes Effect
 Different reinforcers available for different responses
 Can produce faster and stronger discrimination
training than basic forms
 Faster learning and accuracy
DOE
Normally…
Response
Sample
Response
corn
CORN
nothing
Sample
nothing
corn
PEAS
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Pavlov’s Theory
 Physiological interpretation
 Species influenced
 Discrimination training produces establishes areas of
activation in brain
 CS+ --> excitatory regions
 CS- --> inhibitory regions
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Activation
 Stimuli similar to CS+ will excite parts of brain close to
CS+ area
 Dissimilar stimuli will not activate CS+ area
 Result is CR or no CR, respectively
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Inferential Interpretation
 Theory based on inference from observed behaviour
 No independent validation of brain area generation
through conditioning
 Physical proximity of brain areas not needed for
response generation
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Spence’s Theory
 Opponent process theory
 Excitatory (CS+ or S+) and inhibitory (CS- or S-)
gradients
 Net sum effect of gradients
 Resultant behaviour
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Peak Shift
 Change in generalization gradient
 Peak level of responding
 Shift in peak level of responding away from S+ in
direction opposite S-
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shift direction
Responses
Peak Shift
Control (S+ only)
Exp. 1 (S+ & S-)
S+
S28
Peak Shift: Shift Away from SS+ SNet
gradient
+15
+10
+5
Excitatory
gradient
+15
+10
+5
Inhibitory
gradient
-5
-10
-15
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Support for Spence’s Theory?
Responses
 Honig et al. (1963)
 Excitatory and inhibitory gradients
Group 1
S+
SGroup 2
S+
S-
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Lashley-Wade Theory
 Generalization gradients depend on prior experience
with stimuli similar to those used in testing
 Discrimination training --> discrimination because it
teaches subjects to tell the difference between S+ and
other stimuli
 Everyday experiences produce discrimination learning
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Predictions
 Previous experience with stimuli will make
discrimination training of those stimuli easier
 Lack of previous experience will make subsequent
training harder
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Standard Design
 Rear animals under specific environmental condition
 e.g., darkness so no experience with colours
 Give S+/S- training
 Test for generalization gradient
 If gradient of perceptually deprived subjects flatter
than normally reared subjects, then support for
Lashley-Wade theory
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Results
 Ambiguous
 Possibility that special rearing environment produces
neurological damage
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Jenkins & Harrison (1960)
 Group 1 pigeons
 S+ (tone) --> reinf., S- (quiet) --> no reinf.
 Group 2 pigeons
 S+ (tone) --> reinf., no S- (i.e., tone always on)
 Test both groups for generalization to other tones and
to periods of silence
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Results
 Group 1 birds
 Less likely to respond during silent periods
 Show standard generalization gradient to tones
 Group 2 birds
 Responded same amount during tone or silence
 Flat generalization gradient (i.e., no discrimination of
tones)
 Supports Lashley-Wade theory
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Theories
 Pavlov’s
 Lacks support
 Spence and Lashley-Wade
 Both have situations that support and contradict
predictions
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Concept Formation
 Concept: any class of things sharing one or more
defining features
 Defining features allow discrimination between
stimuli within class and outside class
 Concepts can be learned through discrimination
training
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Herrnstein’s Studies
 Stimuli from natural environment
 Train/test many stimuli
 Positive and negative instances
 Pigeons, 80 pictures
 Tree/no tree = positive/negative instances
 Learn discrimination easily
 Generalization test
 Supports concept formation, not memorization
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Concepts of Absolute or Relative
 Concept of absolute
 Learn individual stimuli
 Specify features of members of class
 Concept of relative:
 Learn relationship between stimuli
 Degrees of similarity of features of class members
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Example
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Transposition
 Transfer relational rule to new stimuli set
 Kohler (1939)
Training
S+
S-
Test
transfer
absolute
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Stimulus Control
 Absolute stimulus control
 Successive discrimination tasks
 Relational stimulus control
 Simultaneous discrimination tasks
 Animals do whatever is easiest
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Mental Rotation
 Rotate letter various
amounts and/or inverted
takes longer the greater
the degree of rotation
 Mental rotation of
internal representation
 Gradient of response
times looks like
generalization gradients
R
R
 Determining inversion
R
 i.e., backwards
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Smoking Relapse
 Smoking gives frequent reinforcement
 But, not only physiological effects of nicotine
 Social reinforcement
 Environmental factors become conditioned as S+ for
smoking
 Smoke in many situations, strong generalization
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Experimental Neuroses
 When not possible to distinguish between stimuli in
discrimination conditions
 Consumer situations
 Frustration
 No-choice as option
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