Concepts & Categories
Concepts & Categories
Mental representations of classes of things (Murphy, 2002)
‘Glue’ that hold out world together
What are Concepts for?
Concepts allow us to make sense of the world, and to make accurate predictions about novel items of a category
The Classical View of Concepts
Grounded in philosophical tradition of formal logic
Concepts can be defined by the presence or or absence of features (e.g. if conditions A,B,C and D are satisfied, then object X belongs to category Y)
Necessity and Sufficiency: Properties A, B, C, and D are both necessary and sufficient for object X to be categorized as an instance of Y
Concepts are merely lists of necessary and sufficient conditions
Problems with Classical View
Wittgenstein: What are the necessary and sufficient conditions for the concepts of ‘game’?
Even fairly simple concepts do not have a definition making it difficult to create a concept list
Wittgenstein: What are the the necessary and sufficient conditions for concept of ‘game’
Inconsistency with an individual-
McCloskey and Glucksberg (1978): when asked whether an olive is a fruit, people changed their minds when asked more than once
A dog is a dog is a dog is a dog?
Classical view predicts that all members of a category are ‘equal’. In other words, a Chinese crested dog is equally as good of an example of ‘dog’ as a golden retriever
Typicality and The Fall of the Classical View
Eleanor Rosch and Typicality
Rosch: members of a category differ in terms of how well they represent the category as a whole. A sparrow is a typical bird, whereas a chicken is a atypical bird.
Typical it’s are categorized more quickly and more consistently
What makes an item “typical”?
Family Resemblance- the extent to which exemplar X shares attributes with other exemplars in category A, but not exemplars from carry B, determines ‘typicality’
Typicality
Exemplars of a category can vary widely in terms of how ‘typical’ they are for that category
Categorization behaviour is sensitive to exemplar typicality
Rips, Shoben, & Smith (1973): participants were faster to verify the robin is a bird than ostrich because it is a more typical
Induction: the ability to generalize or extend properties of some category members to others
Premise: Robins have sesamoid bones?
Do sparrows have sesamoid bones?
Rips (1975): People are more likely to believe sparrows have sesamoid bones when the premise involves a typical category member (e.g. robin) than when we premise involves an atypical category member (e.g. penguin)
Typicality and Fear Generalization
Dunsmoor and Murphy (2014): Does stimulus typicality determine how broadly conditioned fear is generalized?
Typical group: Typical mammals paired with aversive shock during conditioning phase
Atypical group: Atypical mammals paired with aversive shock during conditioning phase
Does stimulus typicality determine how broadly conditioned fear is generalized?
Typical mammals paired with aversive shock during conditioning phase
Atypical mammals paired with aversive shock during conditioning phase
Does stimulus typicality determine how broadly conditioned fear is generalized
Broad conditioning makes generalized fear easier
Alternatives to the Classical View
Prototype Theory
Concepts are represented by a categorical ‘prototype’
Prototypes capture the central tendency of a category- ‘summary’ representation
Categorization is based on the similarity between an exemplar and the prototype for that concept
Posner and Keele (1968)
Training Phase
Participants see multiple exemplars from ‘different’ categories
Exemplars consist of low and high distortion items from each ‘category’
Test Phase
Participants are shown new exemplars and the prototypes themselves from each ‘category’ and asked to classify them
Results: Better accuracy for low vs. high distortion exemplars
Accuracy highest for prototypes despite never seeing them
Exposure to exemplars created a ‘prototype’ representation for each category
Categorization of new exemplars was based on comparison to prototype representation
Exemplar Theory
Subjects do not form an abstract ‘prototype’ for each category
Individual exemplars are stored in memory
Categorization is based on the similarity between a new test item and stored exemplars
Whittlesea (1983)
Created categories based in CVCV strings (i.e.FRUIG, NOBAL) as prototypes
Only children of the words are shown and people were told to guess which parent the word came from
Similarity of exemplars to prototype varied by changing one, two, or three letters from category prototype
Do people categorize based on similarity to stored exemplars?
Exemplar theory suggest as we move away from the children of the exemplar it should become more difficult to recognize as belonging to that category
Prototype theory suggests as we move away it should not matter as we are comparing the example to a prototype we’ve made up
Brooks, Norman, Allen (1991)
Seasoned dermatologist and inexperienced medical residents shown labelled pictures of different skin diseases- asked to judge how ‘typical’ each one is of that diagnostic category
The asked to categorize new pictures (unlabeled) that were from the same diagnostic categories, but were either superficially similar or dissimilar from the original images
Results showed that doctors were more likely to diagnose images that looked typical to examples they had just been shown
Alternatives to Classical View
A general consensus regarding the correct theory of concepts (prototypes vs. Exemplars) has yet to be reached
There is evidence for both theories
Some have suggested that when leaning a new category, people initially use individual exemplars to guide their categorization decision , but switch to using a prototype once sufficient experience accrues
Not whoever eve experts rely on similarity between novel exemplars and previously encountered examples (possibly even more than novices)
The Role of Prior Knowledge
Majority of research on concepts has focuses on category leaning with artificial materials
This is done to ensure that prior knowledge can’t influence category learning
Allows researchers to examine ‘pure’ category representations
However, most new concepts that we learn are in some way associated with related prior knowledge
Lin & Murphy (1997)
When groups were told different uses for an item then showed a collection of images of FINSIHHHHHH
Prior knowledge has a large impact on how people categorized objects
How are Concepts Organized?
Categorical knowledge is structured in a nested hierarchy- taxonomic organization
Transitivity- All dogs are mammals, and all mammals are animals. Therefore all dogs are animals
Property Inheritance- all lower categories inherit the properties associated with higher taxonomic
Importance of Basic Categorization
Preferred Level of categorization
Most often used when spontaneously naming an object
Balance the trade between informativeness and distinctiveness
Are often the first categories that children learn based on sorting and naming
Rosch et Al. (1976)
Faster Res to verify category image pairs when category label is at basic category level
Demonstrates that there is seemingly something special about the basic level (default level)
Basic category identification is the last to degenerate in patients with dementia
Categorization and Expertise
Does expertise in a particular domain affect preferred level of categorization?
Expertise on some level represents categorization at its highest level
It takes a dog expert the same amount if time to classify a cocker spaniel as a
Expertise eliminates the advantage FINSIH THIS
Chi Feltovich, Glaser (1981)
Asked novices and experts to classify different types if physics problems
Novices tended to sort problems based on superficial properties, whereas experts tended to sort based on underlying commonalities, forming few overall groups
Experts know when to lump and when to split when appropriate and are not distracted by false commonalities