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PSYC*2650 Ch 9.doc

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PSYC 2650
Anneke Olthof

Monday, Feb 18, 2012 Chapter 9: Concepts and Generic Knowledge Definitions: What Do We Know When We Know What a Dog Is? - we all know what a dog is but what is that knowledge? - one possibility is that we know something akin to a dictionary definition: “a dog is a creature that is (a) mammalian, (b) has 4 legs, (c) barks and (d) wags its tail - the difficulty with this proposal was made clear by Ludwig Wittgenstein who noted that philosophers had been trying for thousands of years to define terms like “virtue” and “knowledge” - since these are subtle, philosophically rich terms they are resistant to definition - he wondered if this was really the problem, he wondered whether we could find defini- tions even for simple ordinary terms e.g. “game” - hide-and-seek (a) is an activity most often practiced by children, (b) is engaged in for fun, (c) has certain rules, (d) involves multiple people, (e) is in some ways competitive and (f) is played during periods of leisure - what about the Olympic Games? the competitors are not children and aren’t necessari- ly having fun - what about card games played by one person? They are played alone without competi- tion - for each clause of definitions, we can find an exception Family Resemblance - what we need is a way of identifying concepts that highlights what the various mem- bers of a category have in common while simultaneously allowing exceptions to whatev- er rule we propose - one way to achieve this is by keeping the content of our definitions but being much more flexible to the use of our definitions - e.g. a dog is a creature that probably has fur, four legs and barks - Wittgenstein’s proposal was that members of a category have a Family Resemblance to each other - imagine the “ideal” for each family, someone who has all of the features, in many fami- lies this person does not exist - each member of a family has at least some features in common with this ideal this is why family members resemble each other - Wittgenstein proposed that the thousands of categories we can thinking about (dog, game) work in the same fashion Monday, Feb 18, 2012 - there may be no features that are shared by all dogs or all games which is why a rigid definition is not possible - we can identify “characteristic features” for each category - the more of these features an object has, the more we believe it is in the category - family resemblance is a matter of degree, not all-or-none Prototypes and Typicality Effects - one way to think about definitions is that they set boundaries for each category Prototype Theory - the best way to identify a category, to characterize a concept, is to specify the “center” of the category rather than the boundaries - categorization would involve a comparison between a test case and the prototype - in some cases a prototype may literally represent the ideal for the category, more com- monly it will be an average of the various category members - different people may have different prototypes Fuzzy Boundaries and Graded Membership - our hypothesis is that what it means to “know” a concept is simply to have some men- tal representation of the concept’s prototype - there is an odd implication here: since the category is characterized by its center/proto- type and not by its boundaries, there’s no way we can say whether something is inside the category or outside - each category will have at best a Fuzzy Boundary, with no clear specification of cate- gory membership and nonmembership - not all category members are equal, objects closer to the prototype are better mem- bers of the category - categories that depend on a prototype have Graded Membership with some dogs be- ing “doggier” than others Testing the Prototype Notion - in the Sentence Verification Task, research participants are presented with a succes- sion of sentences and their job is to indicate whether a sentence is true or false - in most experiments we are interested in how quickly participants can do this task - their speed depends on the number of steps the participants must traverse to confirm the sentence, they respond more quickly for true sentences and familiar categories - speed of response varies from item to item within a category Monday, Feb 18, 2012 - participants make these judgments by comparing the thing mentioned (penguin) to their prototype for that category (bird prototype) - when there is much similarity between the test case and the prototype, participants can make their decisions quickly - in a Production Task we ask people to name as many birds or dogs as they can - they will first locate their bird or dog prototype and ask themselves what resembles it - they will start with the center of the category and work outward from there - the first birds should be the birds that yielded fast response times in the verification task because what matters most in both tasks is proximity to the prototype - birds mentioned later should have slowed response times in verification - this is exactly what happens - members of a category that are “privileged” on one task are also privileged on others - the same happens in a Picture-Identification Task, and a Rating Task - in Typicality studies, participants are asked to judge how typical various category members were for the category - a related pattern emerges if we ask people to think about categories - in a study participants were asked to generate simple sentences about a category e.g. “I like to feed birds in the park” - next the experimenter rewrote the sentences substituting the category name either the name of a prototypical member (robin) or a not-so-prototypical member (penguin) - “I like to feed robins in the park” and “I like to feed penguins in the park” - these edited sentences were shown to different participants and they were asked to rate how silly the sentences seems - the hypothesis is that when people think about a category they are thinking about the prototype - the meaning of the sentence won’t change if we substitute a prototypical category member for the category name - substituting a non-prototypical member may yield a ridiculous proposition Basic-Level Categories - certain types of category are also privileged in their structure and how they are used - there is a “natural” level of categorization, neither too specific nor too general, that we tend to use in our conversations and our reasoning - e.g. you are more likely to say people drive cars to work not Fords or Toyotas - the special status of this Basic-Level Categorization can be demonstrated Monday, Feb 18, 2012 - they are usually represented in our language via a single word, while more specific cat- egories are identified only via a phrase - e.g. chair is a basic-level category, lawn chair is a subcategory - the importance of basic-level categories shows up in our memory errors - in one study, participants read a story and then after a delay their memory was tested - if the story contained specific terms, participants often falsely recalled that they had heard something more general e.g. recalling pants instead of jeans - if the story contained general terms, these were misremembered as being more specif- ic than they actually were e.g. recalling dogs instead of animals - the errors tended to revise the story in the direction of basic-level categorization - basic-level categorization is important for a variety of purposes Exemplars - a broad spectrum of tasks reflects the “graded membership” of mental categories - some categories are “better” than others, and the better members are recognized more readily, mentioned more often, judged more typical - typicality does guide many of our category judgments - e.g. in diagnosing diseases, physicians often seem to function as if asking how this case resembles case of disease X - the greater resemblance to a diagnostic prototype, the more likely the diagnosis will be of that disease - the prototype theory isn’t the only way one can think about these data Analogies from Remembered Exemplars - in some cases categorization can draw on knowledge about specific category mem- bers rather than on more general information about the overall category - categorization is supported by memories of a specific chair, rather than remembered knowledge about chairs in general - this is referred to as Exemplar-Based Reasoning, with an exemplar being defined as a specific remembered instance, or an example - this approach is in many ways similar to the prototype view, according tot each oft hem you categorize objects by comparing them to a mentally represented “standard” - the difference between the views lies in what that standard is - for the prototype theory, the standard is the prototype whereas for exemplar theory, the standard is provided by whatever example of the category comes to mind Monday, Feb 18, 2012 Explaining Typicality Data With an Exemplar Model - people are shown a series of pictures and ask them to decide whether each picture shows a fruit or not - people make their judgments on this by comparing the pictures to specific memories of fruits - if the picture shows an apple, your memory search will be extremely fast, apples are common in your experiences so you’ve have many opportunities to establish apple memories, also these memories will be well primed - if the picture shows a fig your memory search will be more difficult Exemplars Preserve Information About Variability - a prototype is an average, but much information is lost in an average, it does not tell you how variable a set is - you do have some knowledge about the variability within a category and you some- times use this to aid in categorization - you can reflect on what you have seen in the past - exemplars preserve information about variability, prototype does not A Combination of Exemplars and Prototypes - people routinely “tune” their concepts to match the circumstances (exemplars) - people can adjust their categories in fairly precise ways - different settings or perspectives would trigger different memories and bring different exemplars to mind - some evidence favors the idea that part of our conceptual knowledge involves exem- plars - at the same type prototypes also have their advantages, they represent an efficient and economical manner what’s typical for a category - it is entirely plausible that our conceptual knowledge includes both prototypes and ex- emplars so it gains the advantage of each - the mix of exemplar and prototype knowledge may vary from person to person and from concept to concept - exemplar and prototype models rely on the exact same processes - a triggering of memory, then a judgment of resemblance and finally a conclusion based on this The Difficulties With Categorizing vis Resemblance Odd Number, Even Number Monday, Feb 18, 2012 - in our view so far, judgments of typicality and judgments and category membership both derive from the same source - resemblance to an exemplar or prototype - we can also find situations in which there is no relation between typicality and category membership, this is inconsistent with claims so far - researchers asked participants to do several of t
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