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Chapter 9

Chapter 9. Generalization, Discrimination, and Stimulus Control. Variability. Changing conditions Adaptive learning must adapt Transfer behaviour across situations. Generalization. Tendency for a learned behaviour to occur in the presence of stimuli not present during training

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Chapter 9

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  1. Chapter 9 Generalization, Discrimination, and Stimulus Control

  2. 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 • e.g. Little Albert  conditioned fear to white rat, also afraid of terrier, santa mask, fur coat

  4. Discrimination • Tendency for a learned behaviour to occur in the presence of certain stimuli, but not in their absence • Inversely related to generalization

  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 (or even aversive) outcome

  6. Discrimination Training • Any procedure that establishes the ability to discriminate between stimuli • Process by which stimulus control is established

  7. Generalization

  8. 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)

  9. Generalization Gradients • Measure of generalization/discrimination • Respond to stimuli more like trained stimuli • Train on one stimulus, test on others • Techniques/methodologies Train with yellow stimulus Test with all colours Amount of responding

  10. training stimulus (reinforced) probe stimulus (unreinforced) trials Probe Trials • Insert occasional unreinforced test stimulus • Won’t extinguish since there are still many reinforced trials

  11. Extinction Blocks • Train stimulus to asymptote • Blocks of extinction trials • Each stimulus presented once/block • Extinction constant across stimuli

  12. # of responses 15+11+5 = 30 Generalization Gradient 12+7+3 = 22 3+1+0 = 4 50 7 3 1 15 11 40 Responses 30 0 5 10 1 3 20 10 and so on... Light wavelengths 4+3+1 = 8 ExtinctionBlocks 20+15+10 = 45 Training Block 1 4 20 15 12 3 Block 2 Block 3

  13. Reading a Generalization Gradient Response rate Response rate Response rate Stim. continuum Stim. continuum Stim. continuum Broad: Some discrimination Flat: No discrimination Narrow: Lot of discrimination

  14. 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

  15. Generalization Post Extinction • Classical or Operant training, then extinction • Produces reduction in generalization to other stimuli

  16. Generalization of Punishment • Suppression of behaviour via punishment also generalizes • Honig & Slivka (1964) • Pigeons peck coloured disk, get reinforced (7 colours) • Next, peck green disk, get shocked • Gradient forms • Greatest reduction of pecking to “greener” colours Number of Responses

  17. Discrimination & Training Techniques

  18. 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 Don’t Peck Peck Don’t Peck (No Go) Peck (GO)

  19. 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 Delayed MTS Non-match MTS Don’t Peck Peck

  20. 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

  21. 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 Response corn CORN nothing Sample Sample nothing corn PEAS

  22. Theories of Generalization and Discrimination

  23. Pavlov’s Theory • Physiological interpretation • Species influenced • Discrimination training produces establishes areas of activation in brain • CS+ --> excitatory regions • CS- --> inhibitory regions

  24. 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

  25. 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

  26. Spence’s Theory • Opponent process theory • Excitatory (CS+ or S+) and inhibitory (CS- or S-) gradients • Net sum effect of gradients • Resultant behaviour

  27. Peak Shift • Change in generalization gradient • Peak level of responding • Shift in peak level of responding away from S+ in direction opposite S-

  28. shift direction Responses S+ S- Control (S+ only) Exp. 1 (S+ & S-) Peak Shift

  29. S+ S- Peak Shift: Shift Away from S- +15 Net gradient +10 +5 +15 Excitatory gradient +10 +5 Inhibitory gradient -5 -10 -15

  30. Group 1 S+ S- Responses Group 2 S+ S- Support for Spence’s Theory? • Honig et al. (1963) • Excitatory and inhibitory gradients

  31. 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

  32. Predictions • Previous experience with stimuli will make discrimination training of those stimuli easier • Lack of previous experience will make subsequent training harder

  33. 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

  34. Results • Ambiguous • Possibility that special rearing environment produces neurological damage

  35. 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

  36. 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

  37. Theories • Pavlov’s • Lacks support • Spence and Lashley-Wade • Both have situations that support and contradict predictions

  38. Applications

  39. 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

  40. 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

  41. 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

  42. Example

  43. Training Test S+ S- absolute transfer Transposition • Transfer relational rule to new stimuli set • Kohler (1939)

  44. Stimulus Control • Absolute stimulus control • Successive discrimination tasks • Relational stimulus control • Simultaneous discrimination tasks • Animals do whatever is easiest

  45. Mental Rotation • Rotate letter various amounts and/or inverted • i.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 R R

  46. 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

  47. Experimental Neuroses • When not possible to distinguish between stimuli in discrimination conditions • Consumer situations • Frustration • No-choice as option

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