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Reasoning & Decision making

Tobias.Johansson@hkr.se. Reasoning & Decision making. Reasoning. Information. Conclusion. Reasoning - deductive. Information. Premise 1 Premise 2 ……. Premise n Conclusion. Conclusion. Valid deductions = if premises true, then conclusion true

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Reasoning & Decision making

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  1. Tobias.Johansson@hkr.se Reasoning & Decision making

  2. Reasoning Information Conclusion

  3. Reasoning - deductive Information Premise 1 Premise 2 ……. Premise n Conclusion Conclusion Valid deductions = if premises true, then conclusion true A deduction can be valid even if premises are false Only form matters, not content

  4. Reasoning - inductive Conclusion Information Inductive reasoning goes beyond the data Conclusions never follow definitely from observations

  5. Deduction - Syllogisms Categorical syllogisms - Deductions involving All, No, Some All A are B All students are smart people All B are C All smart people are rich Therefore, all A are C Therefore, all students are rich Conditional syllogisms - Deductions involving If…Then If p then q If you talk at the movies you go to prison p You talk at the movies Therefore q You go to prison

  6. Categorical Syllogisms Valid and invalid categorical syllogisms Valid Invalid 1 Some A are B 1 All A are B 2 All B are C 2 Some B are C Con Therefore some A are C Con Therefore, some A are C Some cats are lazy All cats are lazy All who are lazy are dogs Some who are lazy are dogs Therefore some cats are dogs Therefore some cats are dogs Valid, despite false premise

  7. Categorical Syllogisms What kind of errors do people make? - Belief bias - If conclusion true, then syllogism valid No A are B Some C are B Therefore some A are not C Invalid A B No babies are evil No heroin is healthy Some dogs are evil Some chemicals are healthy Therefore some babies are not dogs Therefore some heroin is not chemicals People judge A as valid more often than B, more believable conclusion

  8. Categorical Syllogisms

  9. Conditional Syllogisms Premises Conclusion Valid Performance If p then q p q Yes 97 % If p then q Not q Not p Yes 60% If p then q q p No 40% If p then q Not p Not q No 40%

  10. Conditional Syllogisms Why do people make errors in conditional reasoning? - One reason is lack of falsification strategies - which is affected by the format of the problem To see this, we will look at the Wason four-card problem

  11. Wason four-card problem Potential falsifiers 3 6 P A Indicate the minimum number of cards you have to turn to test the rule: If there is a vowel on one side, then there is an even number on the other side.

  12. Wason four-card problem 3 6 P A 89% 16% 62% 25% If there is a vowel on one side, then there is an even number on the other side.

  13. Beer problem 15 years 27 years Soda Beer If a person is drinking beer, then he/she must be at least 19 years old.

  14. Results – beer vs. abstract (Griggs & Cox, 1982) 15 years 27 years Soda Beer 3 6 P A

  15. Theories Why is the beer task easier? Pragmatic reasoning schema (permissions) - people are familiar with checking permissions Cheating detection - Social exchange theory - In order to monitor social exchange, people have developed cheating detection mechanisms that do not presuppose familarity

  16. Permissions (Cheng & Holyoak, 1985) Typhoid Hepatitis Cholera Typhois Hepatitis Transient Enter If one side says ”Enter”, then the other says ”Cholera” A - Tropical diseases B - Inoculations to ensure protection against disease

  17. Results Checking for inoculations indirectly emphasizes to check for permission to enter the country. This ”permission” group performs much better.

  18. Cheating (Cosmides & Tooby, 1992) Found high performance in conditions that were unfamiliar to the participants and involved cheating. Non-cheating situations reduced performance. Permission schema or cheating detection? - support for both accounts

  19. Induction Observation: Everytime I have met John he is rude. And Steve says the same thing about John. Conclusion: John is a rude person. Observation: Only humans seem to use language. Conclusion: Humans have specially developed language mechanisms that other species do not have.

  20. Strength of induction Representativeness Studying aeroplanes does not tell you much about eagles. Frequency A replicated experiment is better than an unreplicated. QualityAn astronomical story is more coherent than an astrological.

  21. Heuristics Some errors in inductive reasoning may be due to heuristics (even though the heuristics themselves may often be useful) Heuristics - ”Rules of thumb”, ”shortcuts” - Can be adaptive, can lead to error - Computationally attractive - Availability heuristic - Representativeness heuristic - Commitment heuristic

  22. Availability heuristic Which is a more likely cause of death? or Tornado Asthma Asthma is 20 times more likely to kill. About 40% chose tornado. Tornados make the news.

  23. Representativeness heuristic How likely is it that X belongs to the class Y. How similar is X to the prototype of Y. People tend to neglect base rates and focus on characteristics.

  24. Representativeness heuristic Conjunction fallacy Linda - 31 years, single, outspoken, bright - philosophy, concerned with justice - antinuclear demonstrations Which is more probable? A - Linda is a bank teller B - Linda is bank teller and active in feminist movement Many people chose B, because that fits with the feminist stereotype (or did?). But, the probability of two events together cannot be higher than the probability of either.

  25. Commitment heuristic (Lagnado & Shanks, 2003) - More people read tabloids than broadsheets. - The Reporter is the most popular newspaper. - More progressives than liberals read the Reporter. - More Liberals than Progressives read the others. - Overall, 50% of readers are Liberals and 50% progressives.

  26. Commitment heuristic - More people read tabloids than broadsheets. - The Reporters is the most popular newspaper. - More progressives than liberals read the Reporter. - More Liberals than Progressives read the others. - Overall, 50% of readers are Liberals and 50% progressives. A reader is drawn randomly from the population. How likely is it that the person is a Liberal? People answer 50% (correct).

  27. Commitment heuristic - More people read tabloids than broadsheets. - The Reporters is the most popular newspaper. - More progressives than liberals read the Reporter. - More Liberals than Progressives read the others. - Overall, 50% of readers are Liberals and 50% progressives. A reader is drawn randomly from the population. What newspaper would you guess the person reads? Many people guess the Reporter (reasonable). Now, what party does the person vote for? People now judge the person with 80% certainty (instead of 50) to be a progressive!

  28. Commitment heuristic - More people read tabloids than broadsheets. - The Reporters is the most popular newspaper. - More progressives than liberals read the Reporter. - More Liberals than Progressives read the others. - Overall, 50% of readers are Liberals and 50% progressives. A reader is drawn randomly from the population. What type of newspaper would you guess the person reads? Many people guess Tabloid (reasonable). Now, what party does the person vote for? People now judge the person with 38% certainty (instead of 50) to be a progressive!

  29. Commitment heuristic So what? - The amazing thing is that people change their estimates purely on the basis of no information. - They just guess what type of paper, or what specific paper, the person reads. The person is drawn randomly. - They then commit to the truth of this category and assign estimates of political voting thereafter. - The estimates change (up or down) depending on category specificity (specific paper or type of paper) because the category structure is non-aligned. Non-aligned categories Brazil is the most likely country to win the World Cup. At the same time, it is more likely that a European country will win than a South American country.

  30. Commitment heuristic Lagnado and Shanks (2003) study demonstrates that simply asking about a category makes people use the information associated with that category, at that level. It is an extreme form of base rate neglect, because the subjects are not given any misleading information. They are just asked a question without feedback.

  31. Confirmation bias An additional source of induction errors is confirmation bias - tendency to notice information that supports one´s beliefs. Testing rules(Wason, 1960) What rule do I have in mind with these 3 numbers? 2 4 6 Write down three numbers and I will say whether they follow the rule. Tell me when your are certain you have discovered the rule. Most subjects tried numbers thatfollowed their own hypothesis. They key to discovering the rule is to generate numbers that wouldfalsifyone´s hypothesis.

  32. Judgment and decision making Utility approach - people are rational - maximize expected utility Problems - people do not always act rationally - people have limited computational resources - utility is ambiguous - people focus on different aspects dependning on context

  33. Focusing illusion A -How happy are you? B -How many dates did you have last month?

  34. Framing (Tversky & Kahneman, 1981) A disease is about to burst out. If nothing is done, 600 people will die. There are two programs for dealing with the situation. The estimates of the outcomes are as follows: Program A - 200 people will be saved. Program B - 1/3 probability that 600 people are saved, 2/3 probability that noboby will be saved. 72% chose A

  35. Framing A disease is about to burst out. If nothing is done, 600 people will die. There are two programs for dealing with the situation. The estimates of the outcomes are as follows: Program C - 400 people will be killed. Program D - 1/3 probability that nobody will die, 2/3 probability that 600 people will die. 78% chose D

  36. Framing The results are remarkable, since Program A = Program C (same expected utility) Program B = Program D (same expected utility)

  37. Decision justification Offer to buy a vacation package at low price. Options: - buy - don´t buy - pay 5 dollar fee to postpone decision 2 days Pass group - You just passed an exam Fail group - You just failed an exam Indeterminate group - You will find out about exam results in 2 days

  38. - Many chose ”wait” in the indeterminate group. • But the pass and fail groups indicate that outcome doesn´t matter. • People want some justification, before they make the decision that they will make anyway, no matter what the outcome is.

  39. Reasoning, deciding, & the brain Prefrontal cortex (PFC) - sensory information - memory retrieval - working memory - planning - coordination - anticipation - inhibition - relational integration - emotion/response integration

  40. Reasoning, deciding, & the brain Prefrontal cortex (PFC) Perseveration - task switching difficulty PFC damage reduces performance in - card sorting tasks, which require switching strategies - tasks that require connecting different parts - problem solving tasks generally - Problem solving activates PFC in normal participants - More complex problems activate larger areas of PFC.

  41. Reasoning, deciding, & the brain Prefrontal cortex (PFC) Relational integration (Waltz et al., 1999) Task 1 Easy: A is smaller than B, B is smaller than C Hard: A is smaller than B, C is smaller than A Task 2 Easy Medium Hard

  42. Reasoning, deciding, & the brain Prefrontal cortex (PFC) Relational integration (Waltz et al., 1999)

  43. Emotional decisions and the brain Prefrontal cortex (PFC) IOWA gambling task and somatic markers - four decks of cards - associated with different outcomes and probabilities - participants chose cards from any deck for 100 trials - for each choice they win money, or win and lose money A B C D Win every trial: 100 100 50 50 Net result every 10 trials: -250 -250 +250 +250 Status: BADBADGOOD GOOD

  44. VMPFC patients go for the bad decks Control patients show higher SCR (high consistent wins, but higher variable losses also). response to the bad decks (A B) Control patients learn to go for the good decks VMPFC patients do not. (lower consistent wins, but lower variable losses also).

  45. Emotional decisions and the brain Prefrontal cortex (PFC) IOWA gambling task and somatic markers - PFC is thought to integrate somatic markers, emotion-based bodily signals generated from the body, with different response options - PFC damage reduces task performance and somatic markers associated with different choices A B C D Win every trial: 100 100 50 50 Net result every 10 trials: -250 -250 +250 +250 Status: BAD BAD GOOD GOOD

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