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 leavesChairs v. non chairs

What is “Chairness”

Things that are not chairs

I can sit on this

L-shaped like a chair Built to sit on

Also built to sit on

Marcel Duchamp “Fountain” (1917)

On display at the Centre Georges Pompidou in Paris

Categorization Experiments with Pigeons

Train Test

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.

Other categories pigeons can form•Aerial v. non-aerial photos

•Chairs

•Humans

•Cars

•Defective pharmaceutical capsules!

•Oak leaves versus other leaves

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 theoryHuber et al., (1999)

Some birds trained with “compact” stimuli

Some birds trained with “scattered” stimuli

All birds trained on “symmetrical” v. “asymmetrical”

Testing exemplar theoryHuber et al., (1999)

Category: “symmetric” v. “asymmetric”

TEST SESSION

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 (polymorphic rule).

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.

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)

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.