Discriminating prey from background. Some things that get eaten are camouflagedPredators' ability to learn difficult discriminations ? evolution of camouflage. This moth matches the kind of tree bark it rests on.On the web: link to experiments in which bluejays look for moths like this. . Discriminating good vs. poisonous food.
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1. Discrimination learning: Introduction Discrimination learning in nature
How are they learned?
Discriminating complex stimuli in the lab
Do animals learn concepts?
2. Discriminating prey from background
4. Discriminating good vs. poisonous food
5. Avoidance of monarch generalizes to harmless butterflies that look similar
6. More mimicry: flies that look like bees
7. How are discriminations learned? Simple discrimination training methods
Rescorla & Wagner
8. Example of a simple discrimination ? reinforcement (S+)
? no reinforcement (S-)
9. What’s going on? Spence’s theory S+ S-
Excitatory associative strength generalizes
10. Spence: Inhibition generalizes less than excitation
11. Spence: Responding determined by net strength
12. Is discrimination absolute or relational? Train
What was learned?
absolute values (“dark gray is positive”)
relationship (“the darker one is positive”)
Transposition test vs.
13. Spence can predict transposition Train
Test stimulus has more positive strength than old S+
14. Difficulty with Spence’s model Idea of generalization is very powerful
But Spence assumed different stimuli present at the same time were independent
Different from Rescorla and Wagner
Spence gets into trouble with compound stimuli….
15. Feature-positive discrimination A+B ? US, B ? no US
? food ?nothing
A (the light) predicts food; tone does not
ALL positive strength should go to the light
NO CR to B (the tone)
But Spence’s model predicts a CR to B
Rescorla & Wagner is the better model here
16. A possible problem for Rescorla-Wagner A? US, B ? US A+B ? no US
? food ? food ? nothing
This should be impossible for animals to learn!
17. A+, B+, AB- can be learned: How?
19. Pearce causes trouble for R&W: a more complex kind of discrimination A +
Two ways to look at these stimuli:
Sums of elements (R-W)
Unique configurations (Pearce)
20. Pearce’s configural theory A+ AB+ ABC-
Animals encode compounds as wholes.
Generalization occurs between a whole and its parts because they are similar
Here, ABC is more like AB than like A
ABC vs. AB should be learned slower than A vs. ABC
21. Pearce’s configural theory A+ AB+ ABC-
R-W predicts that C (red) will become inhibitory
A(yellow) and B (black) will be excitors
AB will be more excitatory than A alone
22. Results:Support Pearce A+, AB+, ABC-
23. Three Theories of Simple Discrimination Learning: Summary Spence
S+ and S- generalization gradients
Rescorla & Wagner: analyze as elements
Pearce: configural theory
Each correct for some situations (book)
24. More complex stimuli: Category discriminations S+ any slide with a tree
S- any slide with no tree
Train on 40 S+, 40S-
Test with novel slides
Birds perform better than chance on novel slides
i.e. they transfer
What is going on?
25. Category discrimination: What is learned? Category discrimination (or classification) = different behavior toward things in different categories.
This is what the birds are doing.
Concept = cognitive structure that may underlie category discrimination.
Have the birds learned a concept?
There are other possibilities…...
26. Memorizing slides plays a role Pigeons learn small irrelevant details
They can memorize 320 individual slides
Probably don’t see the slides as pictures
Memorizing and generalizing both contribute to acquisition and transfer
Data on next slide
27. Person, flower, car, or chair?
Old and new slides mixed
Birds perform above chance on new slides (generalizing)
Better on old ones (memorizing)
28. What is learned in category learning? Simple associations Feature theory: Excitation and inhibition to features (e.g. green patches, leafy textures)
Transfer because features are shared
Exemplar theory: Excitation and inhibition to whole exemplars as configurations
Transfer reflects stimulus generalization
29. What is learned in category learning? More than simple associations A prototype
Average or typical category member
Transfer reflects similarity to the prototype
Functional categories and mediated generalization (in the book)
33. What is learned in category discrimination? Conclusions No good evidence for processes other than association formation
Associations could involve features or whole exemplars
Probably not prototypes
More in the book