Stimulus Control. Stimulus Control of Behavior Having stimulus control means that the probability of the behavior varies depending upon the stimuli present.

Slide 1 Stimulus Control Slide 2 Stimulus Control of Behavior Having stimulus control means that the probability of the behavior varies depending upon the stimuli present Most of our behavior is under stimulus control –A person that contributes to charity generously while in church may watch every penny spent while at work Slide 3 Slide 4 Discrimination and Stimulus Control Discrimination is demonstrated when the subject responds differently to different stimuli. Train Test Reynolds (1961) Slide 5 Generalization Generalization is when responses to one stimulus occur to other, usually similar, stimuli Generally, as the training and test stimuli become more different responding will decline, producing what is called a generalization gradient Slide 6 Generalization Gradient Guttman & Kalish (1956) –pigeons reinforced for pecking a 580 nm lit key (orange-yellow) (S+) on a VI schedule –A test session was then given where many different colored key lights were presented in extinction S+ Slide 7 Interpreting Generalization Gradients Pigeons trained to peck a moderately bright light (S+) to get food. (S- = dim light) After asymptote is reached, present occasional non- reinforced probe trials at various wavelengths or levels of brightness. Slide 8 Excitatory and inhibitory gradients Pigeons trained to peck at a 800 hz tone (S+), with a 500 nm light S-. Slide 9 1000 Hz Tone always on 1000 Hz Tone S+ / No Tone S- 1000 Hz Tone S+ / 950 Hz Tone S- Slide 10 Peak Shift Effect – Hanson (1959) Slide 11 Spence’s Theory to Account for Peak Shift S+ S- Slide 12 Interdimensional discrimination Discrimination: S+ = 555nm Light; S- = Tone Slide 13 How do we learn discriminations with complex stimuli? Slide 14 Perceptual learning: Examples Pre-exposureDevalueTest --Saline-Lemon  LiCLSucrose-Lemon? LemonSaline-Lemon  LiCLSucrose-Lemon? Another example… Pre-exposureDevalueTest --Saline-Lemon  LiCLSucrose-Lemon? Sal-L/Suc-LSaline-Lemon  LiCLSucrose-Lemon? Slide 15 How do we learn discriminations with complex stimuli? A B A+BA+B Slide 16 Peceptual learning: Mechanism Trial 1Trial 2Trial 3Trial 4Trial 5Trial 6 Total # Presentations Sucrose 3 Saline 3 Lemon 6 Slide 17 Perceptual Learning: The Method of Pre- Exposure Matters Mondragon & Hall (2002) A = lemonB = saltC = sucroseX = quinine Pre-Exposure:AX  BX  AX  BX | CX  CX  CX  CX Devalue:AX  LiCL Test:BX?CX? Question:How much does aversion generalize to BX and CX? Slide 18 What’s going on? Juxtaposition of stimuli clearly matters But why? AX  AX  AX … produces habituation to AX AX  B X  A X  B X …. A Remember: expected things are less salient or associable B Slide 19 Treating Different Stimuli Alike: Categorization “Categorization can be viewed as the ability to treat similar, but not identical, things as somehow equivalent, by sorting them into their proper categories and by reacting to them in the same manner” (Huber, 2001) Classical view: categories united by a defining feature or features (e.g., triangles v. non-triangles) But Consider: Oak leaves v. Non-oak leaves Chairs v. non chairs Slide 20 What is “Chairness” Slide 21 Categorization Experiments TrainTest Scenes with Trees +New Set tree scenes Scenes w/o trees -New Set of no-tree scenes "A pigeon pecks rapidly at a small photograph of Harvard Yard containing trees, buildings, people, sky. After a few seconds, a hopper of grain appears and the pigeon eats. Now the scene changes to a treeless Manhattan street. The bird emits a few desultory pecks, then turns away and paces about. After a minute or so, a picture of a leafy suburban garden appears and the bird begins pecking again." (Shettleworth 1998) Slide 22 Other categories pigeons can form Aerial v. non-aerial photos Chairs Humans Cars Defective pharmaceutical capsules! Oak leaves versus other leaves Slide 23 Human v. Non-Human Slide 24 How do they do it? Exemplar theory: remember category members and then generalize. –Vaughn & Greene 1984: pigeons can remember no less than 320 individual slides! Outdoor scenes randomly assigned to + or – Slide 25 Testing exemplar theory Huber et al., (1999) Category: “symmetric” v. “asymmetric” Slide 26 Exemplar theory: more evidence Cook (1990) –Birds versus Mammals used in slides –Real Category Group: Birds v. Mammals –Pseudocategory Group: Random Bird & Mammals versus Random Birds & Mammals Slide 27 Feature Theory Individual features acquire associative value. Response rate to stimulus depends on total expectancy (V) evoked. Slide 28 Feature Theory: Evidence Cerella (1980):Train: Charlie Brown +, other characters – Test: Keep all features intact, but alter whole Slide 29 Prototype theory Abstract the “ideal” (or average) category exemplar. To test: train with only extreme exemplars, test with average of extremes. Slide 30 Prototype Theory Posner & Keele 1968 Slide 31 Conclusions: Not clear whether birds can extract abstract concepts in categorization experiments Birds may use features and exemplars Another animals may be capable of more complex feats.