Generalization, Discrimination, and Stimulus Control 1 Variability Changing conditions Adaptive learning must adapt Transfer behaviour across situations 2 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 3 Discrimination Tendency for a learned behaviour to occur in the presence of certain stimuli, but not in their absence Inversely related to generalization 4 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 5 Discrimination Training Any procedure that establishes the ability to discriminate between stimuli Process by which stimulus control is established 6 7 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) 8 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 9 Probe Trials Insert occasional unreinforced test stimulus training stimulus (reinforced) trials probe stimulus (unreinforced) Won’t extinguish since there are still many reinforced trials 10 Extinction Blocks Train stimulus to asymptote Blocks of extinction trials Each stimulus presented once/block Extinction constant across stimuli 11 # 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 7 3 1 15 11 Block 3 0 5 10 1 3 and so on... Responses Block 2 40 30 20 10 Light wavelengths 12 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 13 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 14 Generalization Post Extinction Classical or Operant training, then extinction Produces reduction in generalization to other stimuli 15 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 16 17 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 18 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 19 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 20 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 21 22 Pavlov’s Theory Physiological interpretation Species influenced Discrimination training produces establishes areas of activation in brain CS+ --> excitatory regions CS- --> inhibitory regions 23 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 24 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 25 Spence’s Theory Opponent process theory Excitatory (CS+ or S+) and inhibitory (CS- or S-) gradients Net sum effect of gradients Resultant behaviour 26 Peak Shift Change in generalization gradient Peak level of responding Shift in peak level of responding away from S+ in direction opposite S- 27 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 29 Support for Spence’s Theory? Responses Honig et al. (1963) Excitatory and inhibitory gradients Group 1 S+ SGroup 2 S+ S- 30 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 31 Predictions Previous experience with stimuli will make discrimination training of those stimuli easier Lack of previous experience will make subsequent training harder 32 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 33 Results Ambiguous Possibility that special rearing environment produces neurological damage 34 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 35 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 36 Theories Pavlov’s Lacks support Spence and Lashley-Wade Both have situations that support and contradict predictions 37 38 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 39 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 40 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 41 Example 42 Transposition Transfer relational rule to new stimuli set Kohler (1939) Training S+ S- Test transfer absolute 43 Stimulus Control Absolute stimulus control Successive discrimination tasks Relational stimulus control Simultaneous discrimination tasks Animals do whatever is easiest 44 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 45 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 46 Experimental Neuroses When not possible to distinguish between stimuli in discrimination conditions Consumer situations Frustration No-choice as option 47