Discrimination learning: Introduction

Discrimination learning: Introduction PowerPoint PPT Presentation

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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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Discrimination learning: Introduction

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1. Discrimination learning: Introduction Discrimination learning in nature Simple discriminations How are they learned? 3 theories Discriminating complex stimuli in the lab Do animals learn concepts? 3 theories

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 Three theories Spence Rescorla & Wagner Pearce

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 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 + AB + ABC - 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 transposition Configural discriminations 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 A concept 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

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