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Professor Greg Francis 1/2/12 PSY 200: Intro. to Cognitive Psychology 1 Purdue University Representation of knowledge PSY 200 Greg Francis Lecture 23 What is a shoe? Purdue University Concepts  What is the information in Long Term Memory?  May be several different types  We have knowledge about the world  Due to personal experience  Or due to language  Such information must be in some kind of format, which we call concepts  But what are the concepts?  what is the concept of “dog,” “walking,” or “free-market capitalism”? Purdue University Concepts  We will look at three topics in concepts  Definitions (don’t really work)  Prototypes (closer to how humans think)  Exemplars (more likely than prototypes)  And then combinations of concepts  propositions Purdue University Definitions  Plato (and Socrates) spent a lot of effort trying to define terms like virtue and knowledge  they were largely unsuccessful  the 20th century philosopher Wittgenstein wondered if definitions of even simple concepts were possible Purdue University Definitions  Consider the concept shoe, you might define it as Webster’s does  A covering for the human foot, usually made of leather, having a thick and somewhat stiff sole and a lighter top.  Anything resembling a shoe in form, position, or use.  Lots of shoes fit this definition Purdue University Definitions  Consider the concept shoe, you might define it as Webster’s does  A covering for the human foot, usually made of leather, having a thick and somewhat stiff sole and a lighter top.  Anything resembling a shoe in form, position, or use.  But now consider some situations and decide if they are really shoes  A shoe that is intended for display onlyProfessor Greg Francis 1/2/12 PSY 200: Intro. to Cognitive Psychology 2 Purdue University Definitions  Consider the concept shoe, you might define it as Webster’s does  A covering for the human foot, usually made of leather, having a thick and somewhat stiff sole and a lighter top.  Anything resembling a shoe in form, position, or use.  But now consider some situations and decide if they are really shoes  a shoe filled with cement, which cannot be worn  a covering worn on the hands of a person without legs who walks on his hands  And this?  Purdue University Definitions  The difficulty is the same one that Plato and Socrates had trying to define virtue  for any definition you come up with, I can find examples that do not seem to fit the definition  But we all know what a shoe is  so our knowledge of this concept must not be based on some precise definition  Note, scientists can (sometimes) create precise definitions (e.g., a dog is defined by a DNA pattern or by mating abilities)  but the definition is somewhat arbitrary Purdue University Prototypes  Perhaps what defines a concept is similarity among its members  there may be no absolutely necessary characteristics  there may be no absolutely sufficient characteristics  Prototype theory supposes that similarity is judged relative to a prototype example of the concept  e.g., an ideal, average, or most frequent version of the concept Purdue University Prototypes  In prototype theory it is possible for an object to be “more” or “less” a certain concept  Consider the concept “coffee cup” Purdue University Prototypes  In prototype theory it is possible for an object to be “more” or “less” a certain concept  Consider the concept “coffee cup”  and variations (some are “cup-ier” than others) Purdue University Prototypes  In prototype theory it is possible for an object to be “more” or “less” a certain concept  Consider the concept “coffee cup”  and variations (some are “cup-ier” than others)Professor Greg Francis 1/2/12 PSY 200: Intro. to Cognitive Psychology 3 Purdue University Prototypes  In prototype theory it is possible for an object to be “more” or “less” a certain concept  Consider the concept “coffee cup”  and variations (some are “cup-ier” than others) Purdue University Prototypes  In prototype theory it is possible for an object to be “more” or “less” a certain concept  Consider the concept “coffee cup”  and variations (some are “cup-ier” than others) Purdue University Prototypes  Lots of experiments suggest the role of prototypes  Posner & Keele (1968): learning category names for random dot patterns  Discriminate two sets of random dot patterns  Each pattern is a variation of one of two prototype patterns Purdue University Prototypes  Prototypes A B Purdue University Prototypes  variations are made by moving some of the dots variant of A variant of B  subjects learn to classify many different variants  they never see the prototypes themselves Purdue University Prototypes  The key test is done after subjects learn to classify the variants  reaction time for judgment is recorded for stimuli they have never seen before » new variants » the prototypes  reaction time is faster for the prototypes  which suggests that the mental representation of the categories (concepts) are built to favor the prototype of the category  Look at CogLab dataProfessor Greg Francis 1/2/12 PSY 200: Intro. to Cognitive Psychology 4 Purdue University Prototypes  Results are based on data from 191 participants.  Pattern type Reaction time (ms)  Prototypes ! !698.5 !! Variants ! !719.3 !! Unanswered by this (and many other) experiments is what a prototype is:  a “thing” that resides in memory and contains information about the category features?  the result of processing information?  A bit of thought suggests it is the result of processing information Purdue University Prototypes  Consider the types of concepts you can have  and how specific they can be  things: bird, dog, chair, shoe,…  actions: walking, running, sleeping,…  goal-derived: “things to eat on a diet”, “things to carry out of a house in case of a fire”,...  ad hoc: “things that could fall on your head”,


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Purdue PSY 20000 - Lecture 23

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