Generalization, Discrimination, and Stimulus Control

1
Chapter 10

• Generalization, Discrimination, and Stimulus
  Control

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Variability

• Changing conditions
• Adaptive learning must adapt
• Transfer behaviour across situations

3
Generalization

• Tendency for a learned behaviour to occur in the
  presence of stimuli not present during training

4
Discrimination

• Tendency for a learned behaviour to occur in the
  presence of certain stimuli, but not in their
  absence

5
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 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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Examples

• Pavlovian
• Producing CR for stimulus slightly different than
  trained CS
• Operant
• Train in one puzzle box, test in variant box

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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

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Probe Trials

• Insert occasional unreinforced test stimulus

• Wont extinguish

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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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ExtinctionBlocks
431 8
201510 45
Training
Block 1
4
20
15
12
3
Block 2
Block 3
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Reading a Generalization Gradient
Response rate
Response rate
Response rate
Stim. continuum
Stim. continuum
Stim. continuum
Broad Some discrimination/ some
generalization
Flat No discrimination/ high
generalization
Narrow High discrimination/ low
generalization
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Semantic Generalization

• Doesnt 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

• 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)
• Pigeons peck plain disk, get reinforced
• Peck, e.g., green disk, get shocked
• Test with other coloured disks
• Greatest reduction of pecking to greener colours

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Different Discrimination Training Techniques
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Presence/Absence Training

• Successive Discrimination Training
• S S- alternate randomly (S --gt reinf., S- --gt
  extintion)
• Simultaneous Discrimination Training
• S S- presented at same time

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Training

• Matching to Sample (MTS)
• Select from 2 alternatives (comparison stimuli)
  the stimulus that is the same as the sample
• Mismatching
• Like MTS, but pick comparison stimulus not like
  sample
• Delayed Matching to Sample (DMTS)
• Like MTS, but delay between presentation of
  sample and choice

Testing
S
Training
Testing
--Delay period--
S
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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

• Reinforcers available for different responses
• But, reinforcers are different
• Learn multiple three-term contingencies
• Can produce faster and stronger discrimination
  training than basic forms

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Theories of Generalization and Discrimination
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Pavlovs Theory

• Physiological interpretation
• Species influenced
• Discrimination training produces establishes
  areas of activation in brain
• CS --gt excitatory regions
• CS- --gt 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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Spences 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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Peak Shift
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Peak Shift Shift Away from S-
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Net gradient
10
5
15
Excitatory gradient
10
5
-5
Inhibitory gradient
-10
-15
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Support for Spences Theory?

• Honig et al. (1963)
• Excitatory and inhibitory gradients

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Lashley-Wade Theory

• Generalization gradients depend on prior
  experience with stimuli similar to those used in
  testing
• Discrimination training --gt 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) --gt reinf., S- (quiet) --gt no reinf.
• Group 2 pigeons
• S (tone) --gt 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

• Pavlovs
• Lacks support
• Spence and Lashley-Wade
• Both have situations that support and contradict
  predictions

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Applications
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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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Herrnsteins 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)

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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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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
• Cant establish stimulus control
• Consumer situations
• Frustration
• No-choice as option