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Chapter 9

PS260 Chapter 9 - Concepts and Generic Knowledge.docx

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Anneke Olthof

CHAP 9: CONCEPTS & GENERIC KNOWLEDGE DEFINITIONS FAMILY RESEMBLANCE  we need a way of identifying concepts that highlights what the various members of a category have in common. while simultaneously allowing exceptions to whatever rule we propose.  one way to achieve this is by keeping the content of our definitions but being more flexible in our use of definitions.  the probabilistic phrasing of a sentence preserves what is good about definitions - the fact that they do name sensible, relevant features.  but this phrasing also allows some degree of uncertainty.  Wittgenstein's  notion was that members of a category have a family resemblance to each other.  family resemblance: notion that members of a category resemble each other. Family resemblance relies on some number of features being shared but may shift from one subset of the category to another.  imagine the "ideal" for each family - someone who has all of the family's features; this person may not exist  each member of the family has at least some features in common with this idea, and therefore some features in common with other family members  proposed that thousands of categories we can think about (e.g. dog, game, furniture) work in the same fashion.  we can identify "characteristic features" for each category - features that most category members have. PROTOTYPES AND TYPICALITY EFFECTS  one way to think about definitions is that they set the "boundaries" for a category  prototype theory: the claim that mental categories are represented by means of a single "best example", or prototype, identifying the "center" of the category.  may represent the 'ideal' for the category  all judgments about a dog for example, are made with reference to this ideal.  categorization; deciding whether something is a dog or not would involve a comparison between a test case and the prototype represented in your memory.  if there is no similarity between them, then the creature before you is probably not in the category, if there is some similarity, then you identify it in the 'dog' category.  a prototype will be an average of the various category members you have encountered o e.g. the prototype dog will be the average colour of the dogs you've seen, average size of dogs you've seen, etc.  the prototype will serve as a benchmark, an anchor for our conceptual knowledge FUZZY BOUNDARIES AND GRADED MEMBERSHIP  what it means to "know" a concept is simply to have some mental representation of the concept's prototype.  since the category is characterized by its center (the prototype) and not by its boundaries, there's no way we can say whether something is inside of the category or outside.  each category will have a fuzzy boundary with no clear specification of category membership and non- membership  categories that depend on a prototype have graded membership: the idea that some members of a category are "better" members and are more firmly in the category than other members.  e.g. some dogs may be more "doggier" than others TESTING THE PROTOTYPE NOTION  in a sentence verification task, the speed of response varies from item to item within a category.  e.g. response times are longer for sentences like "a penguin is a bird than for "a robin is a bird"  this is because participants make these judgements by comparing the test item to their prototype for that category.  when there is similarity between the test case and the prototype, participants can make their decisions quickly  in a production task (a task where a person is asked to name as many example as possible), according to a prototype view, they will do this production task by first locating their bird or dog prototype in memory and then ask themselves what resembles this prototype.  they will start with the center of the category (the prototype) and work their way outward from there  what matters in both tasks is proximity to the prototype  over and over, in category after category, members of a category that are "privileged" on one task, turn out also to be privileged on other tasks.  various tasks converge in the sense that each task yields the same answer.  category members mentioned early in production task are also "privileged" in a picture-identification task, yielding faster responses.  the same category members are privileged in a rating task.  when people think about a category they are thinking about the prototype for that category  people will come up with appropriate statements for that prototype BASIC-LEVEL CATEGORIES Rosch  argued that there is a "natural" level of categorization, neither too specific nor too general, that we tend to use in our conversations and reasoning.  basic-level categorization: usually represented in our language via a single word, while more specific categories are identified only via a phrase.  e.g. "chair" is basic level, where as "lawn chair" is not so basic  if asked to describe an object, we are likely spontaneously to use the basic-level term  if asked to explain what members of a category have in common with one another, we have an easy time with basic-level categories, but some difficulty with more-encompassing categories.  the importance of basic-level categories also show up in our memory errors.  if a story contains general terms, they're normally misremembered as being more specific than they actually are.  the errors tend to "revise" the story in the direction of basic-level categorization EXEMPLARS  our conceptual knowledge is represented via a prototype and that we categorize by making comparisons to that prototype. ANALOGIES FROM REMEMBERED EXEMPLARS  in some case, categorization can draw on knowledge about specific category members rather than on more general info about the overall category.  exemplar-based reasoning: reasoning that draws on knowledge about specific category members, rather than drawing on more-general info about the overall category.  it can be supported by memories of a specific category  you categorize objects by comparing them to a mentally represented "standard".  for prototype, the standard IS the prototype  for exemplar, the standard is provided by whatever example of the category comes to mind  the judgment is the same: assess similarities between the candidate object and this standard EXPLAINING TYPICALITY DATA WITH AN EXEMPLAR MODEL  exemplar-based can also explain the graded-membership pattern  people make their judgements by comparing the pictures to specific memories of an object, mentally represented examples.  if a picture shows a co
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