Chapter 9 Notes.docx

Page 240-262, 22 pages Page 1 of7 Chapter 9: Knowledge HOW ARE OBJECTS PLACED INTO CATEGORIES? • Concept: A mental representation that is used for a variety of cognitive functions, including memory, reasoning, and using and understanding language. E.g. Concept of cats including what they are, what they look like, etc. • Categorization: The process of placing things into groups of categories. This is essential for helping us understand individual cases we have never seen before, with categories acting as “pointers to knowledge” that once something is categorized a lot of general knowledge can be applied to it while energy can be focused on specifying what’s special about this particular object. • Without categories, we would have to investigate each object or circumstance individually; this would be very complicated and inefficient. Why Definitions Don’t Work for Categories • Definitional Approach to Categorization: Decide whether something is a member of a category by determining whether it meets the definition of a category. • This works well for some things, such as defining a square as “a plane figure with four equal sides”. However, for most natural objects, this does not work as not all members have the same features. • E.g. A chair as “a piece of furniture with a seat, 4 legs, and a back” but there are many chairs which are not designed like this. • Family Resemblance (Wittgenstein): The idea that things in a particular category resemble one another in a number of ways, allowing for some variation rather than setting definite criteria. E.g. A place to sit, a way to support a person’s back for a chair but can be many different sizes and shapes. The Prototype Approach: Finding the Average Case • Prototype Approach to Categorization: Membership in a category is determined by comparing to a “typical”, representative prototype member of the category. This is a statistical approach, based on the average/mean of many instances. • Rosch (1973): The prototype is based on an average of members of a category that are commonly experienced, such as an average of common sparrows, robins, and blue jays for “birds” although the prototype is an average and not an actual member. • Prototypicality describes variations within a category, with high prototypicality meaning a member highly resembles the prototype, while low prototypicality meaning it does not closely resemble the prototype. • Subjects presented with a category title like “bird” and a list of 50 members, with task to rate the extent to which each member represented the category title (1 meaning good example). Results included 1.18 for sparrow, 4.53 for penguin, and 6.15 for bat; for “furniture”, 1.04 for chair and sofa, 2.59 for china closet, 6.68 for telephone Prototypical Objects Have High Family Resemblance • Rosch & Mervis (1975): For a group of common objects, list as many characteristics that you feel are common to them, e.g. “bicycles” have two wheels, pedals, handlebars, are man-powered • When an item’s characteristics have a large amount of overlap with the characteristics of many other items in the category, they have high family resemblance  and thus high prototypicality Page 240-262, 22 pages Page 2 of7 Statements about Prototypical Objects are Verified Rapidly • Smith (1974): Sentence verification technique where subjects are presented with statements and asked to answer “yes” if true, “no” if not, e.g. “An apple is a fruit”. • Typicality Effect: Subjects respond faster for objects that are high in prototypicality (apple for fruit), than objects low in prototypicality (pomegranate). Prototypical Objects are Named First • When subjects are asked to list as many objects in a category as possible, they tend to list the most prototypical members of the category first. Prototypical Objects are Affected More by Priming • Priming occurs when presentation of one stimulus facilitates the response to another. Prototypical members of a category are affected by a priming stimulus more than non-prototypical members. • Rosch (1975): Subjects hear a prime, such as “green”. They then see a pair of coloured circles side by side, and must indicate whether the two circles are the same colour or different. The two circles presented are either 1) the same and good examples of the category (vivid green), 2) the same and poor examples of the category (light green), or 3) different, from different categories (e.g. orange and blue) • Priming with the word “green” resulted in faster “same” judgements for the prototypical good colours, than the nonprototypical poor, light colours. • This is because from priming works to facilitate a subject’s response to a stimulus by providing some of the information they would later need to respond to the stimulus. So subjects imagine a prototypical “good” green when they are primed with the word “green”; thus, prototypicality affects behaviour. The Exemplar Approach: Thinking about Examples • Exemplar Approach to Categorization: Involves determining whether an object is similar to a standard object, but instead of a single “average” stereotype, it’s to exemplars which are actual members of a category that a person has encountered in the past. E.g. Sparrows, robins, and blue jays are each exemplars for “birds” – not a statistical approach with taking an mean • The exemplar approach can explain the typicality effect with faster reaction times, since objects that are more like exemplars are classified faster (family resemblance). • One advantage is that since real examples are used, it can more easily take into account atypical cases. E.g. Instead of comparing a penguin to an “average” bird, we remember there are examples of flightless birds. Thus non-typical examples like ostriches and penguins can be used as exemplars rather than being lost in an average. • The exemplar approach also more easily deals with variable categories, like games – can be covered by variety of exemplars, like football, computer games, marbles, and golf. Which Approach Works Better: Prototypes or Exemplars? • People may use both approaches. In early learning, we may use prototypes and then later take in more exemplar information; in early learning we tend to be poor at taking into account exceptions like ostriches. • For small categories, exemplars may work best (e.g. US presidents), while prorotypes are more efficient for larger categories. IS THERE A PSYCHOLOGICALLY “PRIVILEGED” LEVEL OF CATEGORIES? Page 240-262, 22 pages Page 3 of7 • Hierarchical Organization: Larger, more general categories are divided into smaller, more specific categories. • Although there may be one level that is more psychologically important than others, this may not be the same level for everyone. Rosch’s Approach: What’s special about Basic Level Categories? • There are different levels of categories, ranging from superordinate/global (“furniture”) to basic (“bed”), to subordinate/specific (“double bed”). • When asked to list characteristics of furniture, table, and kitchen table, subjects can only list a 3 features common to all furniture, 0 for all tables, and 10.3 for kitchen table • There is great loss of information about a category from the basic to the global level (3 to 9), and a gain of only a little information from basic to specific (9 to 10.3). Therefore the basic level is psychologically special. • In a naming task when subjects must name 3 pictures, most assign a basic level name, e.g. “guitar” rather than “musical instrument” or “electric guitar”. How Knowledge can affect Categorization • Tanaka & Taylor (1991): Naming task performed on bird experts and nonexperts with objects from many different categories, including of birds. Experts responded the majority of the time by giving specific species names (robin), while nonexperts mostly responded by saying bird • To fully understand categorization, must consider not only properties of the objects, but the learning and experience of the people perceiving these objects. Thus, the level that is psychologically special is not the same for everyone. SEMANTIC NETWORKS: REPRESENTING RELATIONSHIPS BTWN CATEGORIES • Semantic Network Approach: Proposes that concepts are arranged in networks Intro to Semantic Networks: Collins & Quillian’s Hierarchical Model • The network consists of nodes that are connected by links. Each node represents a category or concepts, and links connect related concepts; properties associated with each concept are also indicated. • This is still a hierarchical model since it consists of levels arranged so that more specific concepts, such as “canary”, are at the bottom and more general concepts, such as “animal”, at the top. • To retrieve properties of “canary”, enter at the “canary” concept node. From this node, we see canaries are yellow and can sing. To access more information, more up the link to learn a canary is a bird, and that Page 240-262, 22 pages Page 4 of7 birds have wings, can fly, and have feathers. To access even more, find canary is an animal, and thus has skin. • Cognitive Economy: Storing shared properties just once at a higher level, rather than inefficiently for each node. Exceptions are then encoded at lower nodes, e.g. for “ostrich”, one of its properties is “cannot fly” • This model is concerned with how concepts and properties are associated in the mind, not how they actually correspond to specific structures, nerves, or locations in the brain. • Using the sentence verificat