Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.1 Reasoning and Decision Making Five general strategies Reasoning and Logic Two hypotheses –inherently logical –logic must be learned

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.2 Reasoning and Decision Making Evidence –categorical syllogisms sources of error –conditional reasoning sources of error Bounded rationality

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.3 Five General Strategies Prototype matching –is an instance a member of a category Representativeness heuristic –intuitive predictions –stereotypes –e.g. Is the man, with the glasses and tweed jacket who is reading a book at the lunch table, a truck driver or a college professor? –base rate probabilities Simulation heuristic –imagine a mental model

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.4 Five General Strategies Reasoning by analogy –similarity to past experiences or problems –problem of distinguishing valid from invalid analogies Availability heuristic –frequency versus vividness of examples –examplar search look for counter examples –how easily does an example come to mind

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.5 Reasoning and Logic Reasoning –the thinking involved in determining whether one proposition logically follows from another –attempts to determine the validity of an argument or idea Formal Logic –specify rules of inference that yield valid arguments –validity is independent of content (truth value) –how we “ought” to reason How do we “actually” reason? –Do the rules of formal logic describe actual behavior or do they require careful training?

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.6 Two Hypotheses Information processing stages of reasoning –Stage one - encode a representation in working memory –Stage two - retrieve set of rules to check logic Humans are inherently logical –LTM contains a set of rules of inference equal to formal logic –when people make errors it is because: encode problem incorrectly fail to use inference rules and respond on some other basis Humans are not inherently logical –LTM has no logic rules unless formally trained

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.7 Two Hypotheses Evaluate the hypotheses based on evidence from two types of reasoning –categorical syllogisms –e.g. All M are P All S are M therefore All S are P –conditional reasoning –e.g. If P, then Q P therefore Q

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.8 Categorical Syllogisms Consist of a major and minor proposition (premise) followed by a conclusion A valid syllogism is one in which the conclusion necessarily follows logically from the premises There are four possible figures M-PP-MM-PP-M S-MS-M M-SM-S S-PS-PS-PS-P

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.9 Categorical Syllogisms There are four possible moods –affirmative-universal e.g. All S are P –negative-universal e.g. No S are P –affirmative-particular e.g. Some S are P –negative-particular e.g. Some S are not P There are a total of 256 possible configurations –only 24 of these are valid !

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.10 Sources of Error in Categorical Syllogisms Atmosphere effect –respond to the mood of the premises –whenever at least one premise is negative (particular) then the conclusion chosen tends to be negative (particular) –irrational - not use logic rules just maintain mood (heuristic) –generally true for the valid but can lead to invalid results Content –especially with emotionally laden premises and conclusions –based on believability of conclusion –use biases and prior belief All scientists are honest All women are scientists therefore: All women are honest

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.11 Sources of Error in Categorical Syllogisms Failure to accept the logical task –logic is theoretical NOT empirical –must ignore the truth value of each premise –error in encoding the nature of the problem subjects evaluate the truth not the logic –e.g. Kpelle rice farmers –e.g. children –evidence that education may teach us “when” to reason Failure to discriminate information given in the premise from information retrieved from LTM –unintentionally supplement –e.g. when premise is “Some men are honest”; add “but not all”

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.12 Sources of Error in Categorical Syllogisms Incorrect conversion of premises –assumptions of symmetry –e.g. All A are B does not mean All B are A –real world examples help block incorrect conversions –e.g. All dogs are animals is not converted to All animals are dogs –real world examples may be biased by beliefs e.g. All republicans are rich may convert to All rich people are republicans if you believe this Forgetting premises –three types of common recall errors omit a premise displace terms from one premise to next change quantifiers (some to all)

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.13 Conditional Reasoning Two parts –statement of the condition rule if the first proposition is true then the second is true –statement of the truth value of one of the propositions –e.g. If the world was flat, then you could fall off the edge You fell of the edge Therefore ?

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.14 Conditional Reasoning

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.15 Sources of Errors in Conditional Reasoning Negatives –people have trouble tracing the implications of negation –make more errors when a “not” is present modus tollens and denying the antecedent Confirmation bias –bias to seek answers (evidence ) that confirms supports rather than denies –problem in scientific hypothesis testing –stereotypes and prejudice –e.g. given 2, 4, 6, 8 generate sequences and guess the rule

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.16 Sources of Errors in Conditional Reasoning Confirmation bias continued –whenever we have an hypothesis (belief, prejudice) we seek confirmations not disconfirmations –one piece of disconfirmatory evidence is much more informative than several confirmatory pieces of evidence –problem: scientists have a confirmatory bias which interferes with progress

Cognitive - reasoning.ppt © 2001 Laura Snodgrass, Ph.D.17 Bounded Rationality Human may be inherently capable of logic However –use heuristics –not always accept logical task –processing and memory errors –problems with negatives –“cruising” or “mindlessness” not use our capacity