Chapter 10 Generalization Discrimination and Stimulus Control Variability

Chapter 10 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

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

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

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

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

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)

Generalization Gradients • • Measure of generalization/discrimination Respond to stimuli more like trained stimuli Train on one stimulus, test on others Techniques/methodologies

Probe Trials • Insert occasional unreinforced test stimulus training stimulus (reinforced) trials probe stimulus (unreinforced) • Won’t extinguish

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

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

Response rate Reading a Generalization Gradient Stim. continuum Flat: No discrimination/ high generalization Stim. continuum Broad: Narrow: Some discrimination/ High discrimination/ some generalization low generalization

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

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

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

Different Discrimination Training Techniques

Presence/Absence Training • Successive Discrimination Training – S+ & S- alternate randomly (S+ --> reinf. , S- --> extintion) • Simultaneous Discrimination Training – S+ & S- presented at same time

• Matching to Sample (MTS) – Select from 2+ alternatives (comparison stimuli) the stimulus that is the same as the sample Training Testing S+ • 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 Training Testing --Delay period-S+

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 Schoice, greater discrimination learned

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

Theories of Generalization and Discrimination

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

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

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

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

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

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

Peak Shift: Shift Away from SS+ SNet gradient +15 +10 +5 Excitatory gradient +15 +10 +5 Inhibitory gradient -5 -10 -15

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

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

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

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

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

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

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

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

Applications

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

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

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

Example

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

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

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

Experimental Neuroses • When not possible to distinguish between stimuli in discrimination conditions • Can’t establish stimulus control • Consumer situations – Frustration – No-choice as option