Generalization, Discrimination, and Stimulus Control

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VariabilityChanging conditionsAdaptive learning must adaptTransfer behaviour across situations

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GeneralizationTendency for a learned behaviour to occur in

the presence of stimuli not present during traininge.g. Little Albert conditioned fear to white

rat, also afraid of terrier, santa mask, fur coat

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DiscriminationTendency for a learned behaviour to occur in

the presence of certain stimuli, but not in their absenceInversely related to generalization

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Stimulus ControlStimuli come to exert influence over

behaviourApplication of generalization and

discriminationCS+ and CS-S+ and S-

S+ indicates more reinforcing outcome, S- less reinforcing (or even aversive) outcome

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Discrimination TrainingAny procedure that establishes the ability to

discriminate between stimuliProcess by which stimulus control is

established

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GeneralizationNot a givenCan increase generalization by training in a

variety of settingsGeneralization not always appropriate or

useful (e.g., generalizing violence from video game to real world)

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Generalization GradientsMeasure of generalization/discriminationRespond to stimuli more like trained stimuliTrain on one stimulus, test on othersTechniques/methodologies

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Amount of responding

Train with yellow stimulus

Test with all colours

trials

Probe TrialsInsert occasional unreinforced test stimulus

Won’t extinguish since there are still many reinforced trials

training stimulus(reinforced)

probe stimulus(unreinforced)

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Extinction BlocksTrain stimulus to asymptoteBlocks of extinction trialsEach stimulus presented once/blockExtinction constant across stimuli

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Block 1

Block 2

Block 3

and so on...

Training

4 20 15 12 3

7 3 1 15 11

0 5 10 1 3

4+3+1 = 8

20+15+10 = 45

15+11+5 = 30

12+7+3 = 22

3+1+0 = 4

# of responses

50

30

10

40

20Res

pons

es

Light wavelengths

Generalization Gradient

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Stim. continuum Stim. continuumStim. continuum

Res

pons

e ra

te

Res

pons

e ra

te

Res

pons

e ra

te

Flat:No discrimination

Broad:Some discrimination

Narrow:Lot of discrimination

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Semantic GeneralizationDoesn’t have to be a perceptual stimuliGeneralization of abstract featureAdults 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 ExtinctionClassical or Operant training, then extinctionProduces reduction in generalization to other

stimuli

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Generalization of PunishmentSuppression of behaviour via punishment

also generalizesHonig & Slivka (1964)Pigeons peck coloured disk, get reinforced (7

colours)Next, peck green disk, get shockedGradient formsGreatest reduction of pecking to “greener”

colours

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Number of Responses

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Presence/Absence TrainingSuccessive Discrimination Training

Go-No Go procedure (operant) Sometimes, reinforced for “no go”

S+ & S- alternate randomly (S+ --> reinf., S- --> extintion)

Simultaneous Discrimination TrainingS+ & S- presented at same time

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Peck (GO)Don’t Peck (No Go)Peck

Don’t Peck

Matching to Sample (MTS)Select from 2+

alternatives (comparison stimuli) the stimulus that is the same as the sample

Mismatching (non-matching to sample)Like MTS, but pick

comparison stimulus not like sample

Delayed Matching to Sample (DMTS)Like MTS, but delay

between presentation of sample and choice

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PeckDon’t Peck

Delayed MTSMTSNon-match

Errorless Discrimination TrainingPrevious techniques slowMany mistakes where S- selectedPresent 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 EffectDifferent reinforcers available for different

responsesCan produce faster and stronger

discrimination training than basic formsFaster learning and accuracy

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Sample

Response

Normally…

Sample

Response

corn

nothing corn

nothing

DOE

CORN

PEAS

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Pavlov’s TheoryPhysiological interpretationSpecies influencedDiscrimination training produces establishes

areas of activation in brainCS+ --> excitatory regionsCS- --> inhibitory regions

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ActivationStimuli similar to CS+ will excite parts of

brain close to CS+ areaDissimilar stimuli will not activate CS+ areaResult is CR or no CR, respectively

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Inferential InterpretationTheory based on inference from observed

behaviourNo independent validation of brain area

generation through conditioningPhysical proximity of brain areas not needed

for response generation

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Spence’s TheoryOpponent process theoryExcitatory (CS+ or S+) and inhibitory (CS- or

S-) gradientsNet sum effect of gradientsResultant behaviour

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Peak ShiftChange in generalization gradientPeak level of respondingShift in peak level of responding away from

S+ in direction opposite S-

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S+

Res

pons

es

Exp. 1 (S+ & S-)

Control (S+ only)

shift direction

S-

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S+

+10

+5

-5

-15

-10

+15

+5

+10

+15

S-

Excitatorygradient

Inhibitorygradient

Netgradient

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Support for Spence’s Theory?Honig et al. (1963)

Excitatory and inhibitory gradients

Res

pons

es

Group 1S+ S-

Group 2S+ S-

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Lashley-Wade TheoryGeneralization 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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PredictionsPrevious experience with stimuli will make

discrimination training of those stimuli easierLack of previous experience will make

subsequent training harder

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Standard DesignRear animals under specific environmental

conditione.g., darkness so no experience with colours

Give S+/S- trainingTest for generalization gradientIf gradient of perceptually deprived subjects

flatter than normally reared subjects, then support for Lashley-Wade theory

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ResultsAmbiguousPossibility 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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ResultsGroup 1 birds

Less likely to respond during silent periodsShow standard generalization gradient to tones

Group 2 birdsResponded same amount during tone or silenceFlat generalization gradient (i.e., no

discrimination of tones)Supports Lashley-Wade theory

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TheoriesPavlov’s

Lacks supportSpence and Lashley-Wade

Both have situations that support and contradict predictions

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Concept FormationConcept: any class of things sharing one or

more defining featuresDefining features allow discrimination

between stimuli within class and outside classConcepts can be learned through

discrimination training

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Herrnstein’s StudiesStimuli from natural environmentTrain/test many stimuli

Positive and negative instancesPigeons, 80 pictures

Tree/no tree = positive/negative instancesLearn discrimination easilyGeneralization test

Supports concept formation, not memorization

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Concepts of Absolute or RelativeConcept of absolute

Learn individual stimuliSpecify features of members of class

Concept of relative: Learn relationship between stimuliDegrees of similarity of features of class

members

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No Reinforcer

Reinforcer

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TranspositionTransfer relational rule to new stimuli setKohler (1939)

TestTraining

S+ S- transfer absolute

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Stimulus ControlAbsolute stimulus control

Successive discrimination tasksRelational stimulus control

Simultaneous discrimination tasksAnimals do whatever is easiest

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Mental RotationRotate letter various

amounts and/or invertedi.e., backwards

Determining inversion takes longer the greater the degree of rotation

Mental rotation of internal representation

Gradient of response times looks like generalization gradients

R

RR

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Smoking RelapseSmoking gives frequent reinforcementBut, not only physiological effects of nicotineSocial reinforcementEnvironmental factors become conditioned as

S+ for smokingSmoke in many situations, strong

generalization

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Experimental NeurosesWhen not possible to distinguish between

stimuli in discrimination conditionsConsumer situations

FrustrationNo-choice as option

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