1. 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) Important feature of categories: sharp boundaries 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

2. What is “Chairness”

3. Things that are not chairs I can sit on this L-shaped like a chair Built to sit on Also built to sit on

4. Marcel Duchamp “Fountain” (1917) On display at the Centre Georges Pompidou in Paris

5. Categorization Experiments with Pigeons TrainTest Scenes with Trees +New Set tree scenes Scenes w/o Trees -New Set of no-tree scenes When a member of the positive category is shown, pecks are rewarded on VI schedule. When a member of the negative category is shown, each peck extends the trial and is not rewarded.

6. Object Recognition Rotational invariance Size Invariance Translational invariance We recognize an object as being “the same” even as its image on our retina changes

7. Human v. Non-Human

24. Other categories pigeons can form Aerial v. non-aerial photos Chairs Humans Cars Defective pharmaceutical capsules! Oak leaves versus other leaves

25. 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 –

26. Testing exemplar theory Huber et al., (1999) Some birds trained with “compact” stimuli Some birds trained with “scattered” stimuli All birds trained on “symmetrical” v. “asymmetrical”

27. Testing exemplar theory Huber et al., (1999) Category: “symmetric” v. “asymmetric” TEST SESSION

28. 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

29. Feature Theory Individual features acquire associative value. Response rate to stimulus depends on total expectancy (V) evoked (polymorphic rule).

30. Feature Theory: Evidence Cerella (1980):Train: Charlie Brown +, other characters – Test: Keep all features intact, but alter whole

31. Prototype theory Abstract the “ideal” (or average) category exemplar. To test: train with only extreme exemplars, test with average of extremes.

32. Prototype Theory Humans respond more to the triangle than to the others (Posner & Keele 1968) Pigeons respond less to the triangle than to the others (Huber & Lenz, 1996)

33. 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.