What is a concept?

• Part of semantic memory (vs. episodic memory)• A class of items that seem to belong together

– ‘dog’, ‘balloon’, ‘terrorist’ (things) – ‘tall’, ‘ugly’ (properties) – ‘walk’, ‘jump’ (actions)

• A mental construct (vs. the outside world)• Abstract knowledge

• How are things clustered into categories?

• Based on similarity big birdn sesame jump)t

Sesamestreet_bigbird

Sesametstree_jump

German Shepherd

fidoprince puppy

formerly known as prince

bingojessie

- Abstract representation

What does it mean to know what a ‘dog’ is?

• Classical View:– To know what a ‘dog’ is, is to know its definition.– Dog = mammal, four legs, barks, wags tail – These properties are

• Singly necessary: every member must have them• Jointly sufficient: everything that have them is a member

– Categories have sharp boundaries • Either you are in or you are out

– Categories have a homogeneous space• Everyone that is ‘in’ is equally good member of the category

Classical View: Problems• Good definitions are hard to find! • Example: A bachelor is an unmarried man

– is my kid a bachelor? Adult – is the pope a bachelor? intention to get married

• Some members are more typical than others (Categories have internal structure) – Basketball, golf, mini-golf– Cup, tea cup, stanley cup, C-cup

Solution:– There are no defining properties, but rather– properties characteristic of the group (typical features)

Birdie birdBird?

• Is Pluto a planet or a ‘dwarf planet’? Npr(silly question)

Mother:- ‘working’ mother- ‘adoptive’ mother

• A prototype:– is an abstract representation (usually the average)– contains salient features that are true of most instances

e.g., birds usually can fly (but not always) =>

‘ability to fly’ is a salient feature of the category ‘bird’A prototypical bird is one that flies (& have feathers, etc)A bird that doesn’t fly is atypical (weird: penguin, ostrich)

• Prototype Theory (Rosch)– specify the “center” of the category, – leave ‘fuzzy’ boundaries – graded category membership (tea cup vs. Stanley cup)

• some categories don’t obey these properties– Things that have ‘essence’ (‘human’ ‘marriage’)??

Prototypes and Basic Level

• Physical Object• Living Thing• Animal• Mammal• Carnivore• Canine• Dog• Australian Shepherd

Superordinate

BASIC

things

Vehicle Furniture Animal

Truck

Pickup Truck

Chair

Kitchen Chair

Fish

Trout

Subordinate

Living Thing

Animal Plant

Fish Bird

Trout Salmon

Superordinate: Low similarity within category (low coherence) Animals look different from each other

BASIC level:-High similarity within category All fish look the same

-Low similarity between categoriesFishes look different from other animals

Subordinate: High similarity between categories (low discriminability)Different types of fish look similar to each other

Except to Experts

• Properties of the Basic Level Categories– Maximize within-category similarity– Minimize between- Category similarity– Maximum level of abstraction while

maintaining physical similarity– Shorter name

Basic Level

• “There is generally one level of abstraction at which the most basic category cuts can be made. ..

• …the basic level of abstraction in a taxonomy is the level at which categories carry the most information.” Rosch et al. 1976)

• One privileged level

Why are concepts useful? Functions• Coding of experience: Classification of items as members of the

same category

– Reduces cognitive demands – Facilitates communication – Inductive Inferences

• Natural kinds vs. artifacts – Combines to create complex categories

• Contact lens• Digital Camera

Concepts and Misconceptions

• Stereotypes (social categories)– Blacks, Republicans, Arab Nations– Stereotypes reduce complexity– The reduction in complexity leads to errors

• Extreme examples of the category are more heavily weighted – same is true for some other categories, e.g. trees

• Within-category variability is underestimated– “all Bush supporters are the same”

• Insensitivity to disconfirmation– Members who challenge the stereotype are thought to be ‘special cases’ (poor examples of the

category). Therefore – they are thought not to be diagnostic of the category.– “No women is a good soldier. A good female soldier, is less of a woman”

• Stereotypes are more stable than is warranted by evidence – test-retest reliability: after one week .94 after 4 years .92

• Illusory correlation– Distinctive behavior - Distinctive individuals are perceived to ‘go together’ even when they are

independent (e.g., antisocial behavior - blacks)• Misattribution (race – poverty – education- neighborhood)

• Racial stereotypes are thought as ‘essential’ categories

Stereotypical biases