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Stimulus Control
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
Discrimination
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Discrimination and Stimulus Control• Discrimination is demonstrated when the subject
responds differently to different stimuli.
Train
Test
Reynolds (1961)
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
Generalization GradientGuttman & Kalish (1956)
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– 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+
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.
Excitatory andinhibitory gradients
Pigeons trained to peck at a 800 hz tone (S+), with a 500 nm light S-.
1000 Hz Tone always on
1000 Hz Tone S+ / No Tone S-
1000 Hz Tone S+ / 950 Hz Tone S-
Peak Shift Effect – Hanson (1959)
Spence’s Theory to Account for Peak Shift
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ExcitatoryDifference
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Interdimensional discrimination
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PseudodiscrimDiscrimination
Discrimination: S+ = 555nm Light; S- = Tone
How do we learn discriminations with complex stimuli?
Perceptual learning: Examples
Pre-exposure Devalue Test
-- Saline-LemonLiCL Sucrose-Lemon?
Lemon Saline-LemonLiCL Sucrose-Lemon?
Another example…
Pre-exposure Devalue Test
-- Saline-LemonLiCL Sucrose-Lemon?
Sal-L/Suc-L Saline-LemonLiCL Sucrose-Lemon?
How do we learn discriminations with complex stimuli?
A BA+B
Peceptual learning: Mechanism
Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Trial 6Total #
Presentations
Sucrose Sucrose Sucrose 3
Saline Saline Saline 3
Lemon Lemon Lemon Lemon Lemon Lemon 6
Perceptual Learning: The Method of Pre-Exposure Matters
Mondragon & Hall (2002)
A = lemon B = salt C = sucrose X = quinine
Pre-Exposure: AXBXAXBX | CXCXCXCX
Devalue: AXLiCL
Test: BX? CX?
Question: How much does aversion generalize to BX and CX?
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 leavesChairs v. non chairs
Categorization Experiments
Train Test
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)
Other categories pigeons can form•Aerial v. non-aerial photos
•Chairs
•Humans
•Cars
•Defective pharmaceutical capsules!
•Oak leaves versus other leaves
Human v. Non-Human
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 –
Testing exemplar theory
Huber et al., (1999)
Category: “symmetric” v. “asymmetric”
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
Feature Theory
• Individual features acquire associative value.
• Response rate to stimulus depends on total expectancy (V) evoked.
Feature Theory: Evidence
Cerella (1980): Train: Charlie Brown +, other characters –
Test: Keep all features intact, but alter whole
Prototype theory
• Abstract the “ideal” (or average) category exemplar.
• To test: train with only extreme exemplars, test with average of extremes.
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.
