Categories and categorization

: DEFINING-ATTRIBUTE THEORIES OF CONCEPTS

• The meaning of a concept can be captured by a conjunctive list of attributes (i.e., a list of attributes connected by ANDs).

• These attributes are atomic units or primitives which are the basic building blocks of concepts.

• Each of these attributes is necessary and all of them are jointly sufficient for something to be identified as an instance of the concept.

• What is and is not a member of the category is clearly defined; thus, there are clear-cut boundaries between members and non-members of the category.

• All members of the concept are equally representative.

• When concepts are organised in a hierarchy then the defining attributes of a more specific concept (e.g., sparrow) in relation to its more general relative (Its superordinate; e.g., bird) includes all the defining attributes of the superordinate.

: CONCEPT HIERARCHIES

• People use hierarchies to represent relationships of class inclusion between categories; that is, to include one category within another (e.g., the category of chair within the category for furniture).

• Human conceptual hierarchies have three levels;

a superordinate level (e.g., weapons, furniture),

a basic level (e.g., guns, chair),

a subordinate level of specific concepts (hand-guns, rifles, kitchen chairs, armchairs).

• The basic level is the level at which concepts have the most
“distinctive attributes” and it is the most cognitively economic; it is the level at which a concept’s attributes are not shared with other concepts at that level.

• Categories at the basic level are critical to many cognitive activities; for example, they contain concepts that can be interacted with using similar motor movements, they have the same general shape, and they may be associated with a mental image that represents the whole category.

• The position of the basic level can change as a function of individual differences in expertise and cultural differences. 

A schematic diagram of the sort of hierarchical, semantic networks proposed by Collins and Quillian (1969)

PROTOTYPE THEORY OF CONCEPTS

• Concepts have a prototype structure; the prototype is either a collection of characteristic attributes or the best example (or examples) of the concept.

• There is no delimiting set of necessary and sufficient attributes for determining category membership; there may be necessary attributes, but they are not jointly sufficient; indeed membership often depends on the object possessing some set of characteristic, non-necessary attributes that are considered more typical or representative of the category than others.

• Category boundaries are fuzzy or unclear; what is and is not a member of the category is illdefined; so some members of the category may slip into other categories (e.g., tomatoes as fruit

or vegetables).

• Instances of a concept can be ranged in terms of their typicality; that is, there is a typicality gradient which characterises the differential typicality of examples of the concept.

• Category membership is determined by the similarity of an object’s attributes to the category’s prototype.