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Chapter 7

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University of Guelph
PSYC 3100
Hank Davis

Chapter 7 –Cognition Categorization  We group things, places, situation, and even people into categories  The ability to learn concepts is affected by the number of relevant and irrelevant dimensions  However Eleanor Rosch said that many natural categories—categories people spontaneously form outside the psychology laboratory—have an internal structure; this is demonstrated through typicality Typicality  In the real word categories items exhibit different degrees of membership o Categorizes are fuzzy o For example a robin is central/typical of the category, but penguin would be on the periphery  Rosch said natural categories are structured by typicality, that is, by a recognition that some items are more and some items are less central to the category  Typicality must affect how items are stored in memory because reaction time depends on typicality  Typicality affects how we think about the item o Things that are more typical have more common features  Typicality-based categories reflect the nested hierarchy of relatedness among living things  Our fuzzy categorization is very good at recognizing natural kinds—the kinds that evolution creates  In an experiment by Boster and D’Andrade ornithologists, college students and members of a South African tribe were told to categorize groups of birds and all have similar groupings subjects were in fact recognizing that pattern of relatedness  Boster also stated that typicality is better predicted by the number of closely related species than it is by how common the bird is  Our categories have a nested structure including typical and progressively more atypical representativeness. This category structure is highly correlated with the actual structure of evolutionary relatedness among living things, so this cognitive architecture may well have evolved to reflect the world around us  Typicality based categories can give us an evolutionary appropriate way of using out experience to anticipate the properties of living things  It remains to be see whether all categories are organized by typicality Memory  An efficient memory would forget the less useful items  For our memories to function efficiently, we have to forget much of our experience or ignore it in the first place Practice and Retention Effects  People find it easier to retrieve information they have been exposed to many times  this is the practice effect  We are better able to recall recent information  this is the retention effect  Both these effects seem to be best described by power functions o Memories decay rapidly are first and then more and more slowly, as a function of time taken to a negative power Spacing Effects  Items that are tested soon after their last presentation are recalled more accurately of the series of presentations was at short intervals, but items tested longer after the last presentation are recalled more accurate when the presentations were at longer intervals Modeling the Demands on Memory  Does this pattern of retention serve the goal of making the most needed memories the most accessible?  To see what an ideal memory would have to do, Anderson and Schooler studied the events in the world  Took words utters by the new York times, parents and an email o Each word is a power function; the pattern of probability that a word will appear in a paternal utterance, newspaper is a power function of the number of utterances since it last appeared. The probability of getting an email from a person is a power function of when you last received an email from them  Thus our memories decay in the power-function way that is does because this pattern of decay matches the likelihood that we will need to recall them  Testing the spacing effect o To see if the real world clustered in the same way Anderson and Schooler measured 2 things: the presentation interval between two prior occurrences of the same word or name and the test interval, that is, the number of days since its most recent occurrence. Also need to assess how these 2 measures affect the probability that a work or name would appear in the next headline (or utterance or email)  Results: a pattern that strongly paralleled the spacing effect  The practice, retention, and spacing effects seem to match the pattern of real world events Reciprocity: an evolutionary explanation for altruism  Reciprocity  evolve via group selection o ―you scratch my back ill scratch yours‖  The altruist gets a cost and the recipient of the altruism gets a benefit o Altruists are weeded out by selection  Trivers (1971) : costs must be small compared to benefits, and the altruists and recipient must regularly exchange roles o This turns short term altruism into long-term cooperation How can reciprocal altruism pay?  Cheaters are those that take when they need but do not give when others need  The key to altruism is reciprocity: behave altruistically towards other altruists, and withhold altruism from those who do not pay you back  Reciprocal altruism can spread if altruism is withheld from cheaters  Reciprocal altruism is not very likely to evolve unless individuals can recognize each other o Also unlikely to evolve in large, open societies where the same individuals seldom meet twice Game Theory Provides a Formal Model of Reciprocity  Game theory is a branch of math for studying situations in which individuals have conflicting wants  The prisoner’s dilemma  the ―players‖ are 2 people charged with theft and they both know they are guilty but agreed they would remain silent about the crime if caught. If they don’t confess they get 1 year in jail, if they confess they get 5, but of one rats the other person out, he gets off scot free and his partners spends 10 years in jail  Iterated Prisoners Dilemma provides an opportunity to punish cheaters  The tit-for-tat strategy  cooperates on the first round and then does whatever its opponent did on
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