The principles
Two general and basic principles are proposed for the formation of categories:
- Has to do with Function of category systems and asserts that the task of category system is to provide maximum information with the least cognitive effort
- Has to do with the structure of the information so provided and asserts that the perceived worlds comes as structured information rather than as arbitrary or unpredictable attributes Cognitive economy
The first principle contains common sense notion that as an organism, what one wishes to gain from one’s categories is a great deal of information about the environment while conserving finite resources as much as possible
- One purpose of categorization is to reduce the infinite difference among stimuli to behaviourally and cognitively usable proportions
Perceived world structure
The second principle of categorization asserts that unlike the set of stimuli used in traditional laboratoryconcept attaining tasks, the perceived world is not an unstructured total set of equiprobable co-occurring attributes –rather the material objects of the world are perceived to possess high correlational structure -What attributes will be perceived given the ability to perceive them is undoubtedly determined by many factors having to do with the functional needs of the knower interacting with the physical and social environment
Category systems have both vertical and horizontal dimensions
Vertical dimension: concerns the level of inclusiveness of the category, the dimension along which the terms collie, dog, mammal, animal and living thing vary
Horizontal dimension: concerns the segmentation of categories at the same level of inclusiveness – the dimension on which dog, cat, car, bus, chair, sofa vary
- Not all possible levels of categorization are equally good and useful
The vertical dimension of categories Basic-level objects
Category: a number of objects that are considered equivalent Pdog, animal)
Taxonomy: is a system by which categories are related to one another by means of class inclusion Pthe greater the inclusiveness of a category within taxonomy, the higher the level of abstraction)
Level of abstraction: Within taxonomy refers to a particular level of inclusiveness PLinnean system for the classification of animals
Cue validity is a probabilistic concept: the validity of a given cue x as a predictor of a given category y Pthe conditional probability of y/x) increases as the frequency with which cue x is associated with categories other than y increases and decreases as the frequency with which cue x is associated with category y increases
- A category with high cue validity is more differentiated from other categories than one of lower validity Category resemblance: which is defined as the weighted sum of the measures of all of the common features within category minus the sum of the measures of all of the distinct features. Distinct features include those that belong to only some members of a given category as well as those belonging to contrasting categories
A working assumption of the research on basic objects is that:
- In the perceived world, information rich bundles of perceptual and functional attributes occur that form natural discontinuities
- Basic cuts in categorization are made at these discontinuities
-Superordinate categories have lower total cue value validity and lower category resemblance than do basic level categories, because they also share most attributes with contrasting subordinate categories PTversky believes they tend to be combined because the weight of the added common features tend to exceed the weight of the distinctive features)
Four investigations provided converging operational definitions of the basic level of abstraction: -Common attributes
-Common Motor movements
-Similarity in shapes
-Identifiability of averaged shapes
Common attributes
Examples of taxonomies used in basic object research, the results of the study predicted: very few attributes were listed for the superordinate categories Pfurniture), a significant greater number listed for the supposed basic-level objects Pchair table), and not significantly more attributes listed for subordinate level objects Pkitchen chair, dining room table) than for basic level
-The basic level as defined by numbers of attributes in common, did not occur at the level of the folk generic but appeared at the level we had originally expected the superordinate ** most in this category
Motor movement
- How we interact and use objects, concrete objects take the form of motor movements
- For example, when performing the action of sitting down on a chair, a sequence of body and muscle movements are typically made that are inseparable from the nature of the attributes of chairs, we sit on the majority of chairs using the same motor programs
Similarity in shapes
-The appearance of the objects
Results showed that the ratio of overlapped to nonoverlapped area when two objects from the same basiclevel category Pe.g two cars) were superimposed was far greater than when two objects from the same superordinate category were superimposed Pe.g. car and motor cycle)
- The gain obtained by shifting from basic level to subordinate objects was significantly less than the gainobtained by shifting from superordinate to basic level Plarger difference)
Identifiability of averaged shapes
- The basic level is the most inclusive level at which shapes of objects of a class are similar and can be recognized
- Results from above show basic objects level were the most general and conclusive categories at which the objects depicted could be identified
Implications for other fields
-Imagery: Isomorphic mental image to the appearance of members of the class as a whole, signal detection paradigm and priming paradigm were used to verify that basic objects appear to be the most abstract categories for which an image could be reasonably representative of the class
-Perception: objects may be first seen or organized as members of their basic category, and that only with the aid of additional processing can they be identified as members of their superordinate or subordinate category
-Development: classification into categories is over-determined because perception, motor movements, functions and iconic images would all lead to the same level of categorization -> thus basic objects should be the first categorization made by children Pgeneral in children) basic-level of grouping “seen as the same type of thing” ie a chair
-Language: people use the most useful and basic names to name items even if they new the subordinate names
- In sign language basic level categories that were most often coded by single signs and superordinate but subordinate categories that were missing
The horizontal dimension: internal structure of categories: prototypes
-Categories do not have clear boundaries
-Categorical judgements become a problem only if one is concerned with boundaries
-Prototypes are the members of a category that most reflects the redundancy structure of the category as a whole
- Prototypes of categories means the clearest case of category membership, defined by people’s judgements of goodness of membership in the category
A lot of confusion about prototypes has arisen from two sources:
- The notion on prototypes has tended to become reified as though it meant a specific category member or mental structure
- the empirical finding about protptypicality have been confused with theories of processing, for example there has been a failure to distinguish the structure of categories from theories concerning the use of that structure in processing
For categories of concrete objects a reasonable hypothesis is that prototypes develop through the same principles such as maximization of cue validity and maximization of category resemblance as those principles governing the formation of the categories themselves
- The more prototypical of a category a member is rated the more attributes it has in common with other members of the category
Effects of Prototypicality on psychological dependent variables
Prototypicality of items within a category can be shown to affect virtually all of the major dependent variables used as measure in psychological research
Speed of processing: reaction time
- One of the most widely used processing in the semantic memory
- Rate of learning of new material and the naturally obtainable measure of learning reflect in developmental order are two of the most pervasive dependent variables in psychological research – Using a “category-membership verification technique” Rosch found that difference in reaction time to verify good and poor members were far more extreme for 10 year olds then adults -> this demonstrates that the children had learned the category membership of the prototypical members earlier than that of other members
- Prototypical items were the first and most frequently produced items
Effect of advance information on performance: set, Priming
For colours, for natural superordinate semantic categories and for artificial categories, the degree of Prototypicality determines whether advanced information about the category name facilitates or inhibits responses in a matching task
The logic of natural languages use of category terms: hedges, substitutability into sentences, superordination in ASL
-Prototypicality as a variable indicates that prototypes must have some place in psychological theories of representation, processing and learning, however prototypes themselves do not constitute any particular model of processes, representation or learning
Hedges: term such as almost, virtually, technically, sort of.
Substitutability into sentences: The meaning of works is intimately tied to their use in sentences, for example a bird is on my window sill; sparrow-> substituted for bird-> but does not work if we use turkey
Productive superordinate in ASL: when superordinate goals in ASL are generated by means of a partial fixed list of category members, those members are the more prototypical items in the category
Prototypes themselves do not constitute any particular model of processes, representation or learning because:
- To speak of a prototype at all is simply a convenient grammatical fiction, what are really referred to are judgments of degree of prototypicality, only in some categories is there a literal single prototype 2. Prototypes do not constitute any particular processing model for categories, prototypicality do contribute to processing as a constraint but do not determine models of representation
- Prototypes do not constitute a theory of representation of categories
- Although prototypes must be learned, they do not constitute any particular theory of category learning
Two problematic issues
The nature of perceived attributes
The role of context in basic level objects and prototypes
-It is not clear just what experimentally defined context will affect what dependent variables for what categories
-The basic level of abstraction is that level of abstraction that is appropriate for using, thinking about or naming an object in most situations in which the object occurs, when the context is not specified in an experiment, people must contribute their own context
The role of objects in events
Previous events have been studied primarily from two perspectives in psychology:
-Ecological
-Social psychology
Think of script or events as the level of theory at which we can specify how culture and social structure enter individual mind
- Study on asking to student to remember past event as far back as they could, result found that Furth and further in the past appeared fewer and fewer events were remembered although the type of unit for those that were remembered remain the same
- A good candidate for the basic level of abstraction for events is the type of unit into which the students broke their days
-To Bransford and Johnson context cues are actually the name of basic level events and that one function of hearing the event name is to enable the reader to translate the superordinate terms into basic-level object and actions. Such a translating appears to be necessary aspect of our ability to match linguistic descriptions to world knowledge in a way that produces the “click of comprehension”