PSY 341 Lecture Notes - Lecture 17: Confirmation Bias, Deductive Reasoning, Belief Perseverance
4/24/18
Confirmation Bias
•Involved in belief perseverance in many domains
• Suggests that confirmation biases play a role in sustaining propaganda / stereotypes belief
• We often fail to see disconfirmation and seek confirmation. Seeking Confirmation is a type of heuristic / bias
Reasoning: Deductive Logic
• 2 kinds of investigations
• Categorical Syllogisms
• Arguments are either valid or invalid
•Validity based ONLY on form and inferences rules
•Conclusions are either sound (true) or unsound (untrue)
•Based on validity AND truth of the 2 premises
• Valid argument, but conclusion unsound / false
• Quantifiers / Operators in Syllogisms - Quantifiers (all, some, few..) and operators (negation: no,
none, not) have big influence on how well people do syllogical reasoning
• Conditional (if-then) Statements: a failure to mentally construct / convert premises and conclusions into
all logic in general
• Normative Model: formal logic systems used to determined validity of arguments
• Validity of argument determined by ONLY the arguments’ form / structure and using some inference rules to
determine truth of conclusion
• If you follow the rules of the formal system, you are guaranteed to come to a valid conclusion about
which the truth or falsity can be accurately determined.
Conversion Bias: a failure to mentally construct premises and conclusions into ll logical possibilities
• This failure is another the reason people have problems with some syllogisms & with deductive logic in general
• What causes conversion (failure of imagination) biases?
•Can be due to faulty comprehension of premises
•Mental laziness: Don’t construct all possible set the premises / aspects of the problem)
• Failure of imagination is another possible reason: Some set relations are more highly available / familiar
than others, therefore we think we’ve uncovered all alternatives when we access them.
Complexity of Mental Models: the more complex (ie more models / set relations that need to be computed), the
more errors in reasoning
•WHY the errors?
• Diff btwn how qualifiers are interested in everyday language & how they are interested logically (eg,
some)
• Processing limitations?
•Failure to construct all alternatives due to lack of memorial resources
•Maybe, but there’s more to it because:
•Errors are systemic, not random.
•Types of errors are evidence for b i a s e s
Atmosphere (Similarity) Bias
• Validity or Invalidity judgement based in the degree of similarity btwn the form of the premises and the form
of the conclusion
• When similar, judgements of validity increase.
• When dissimilar, judgements of invalidity increase
• When the going gets tough, some people give up and use heuristics
• Arguments is invalid
•When conclusions and premise share quantifiers &/ot operators, then take on the same “ atmosphere”
and thus are more likely to be judged valid.
Summary for Syllogistic Reasoning
•Conversion Bias (failure to convert premises into all possibilities)
•Errors due to incomplete evaluation of possibilities cap. w/ qualifiers like all and some operators like not
• We sometimes rely on heuristics (eg atmosphere bias) when deductions are hard
• Atmosphere (Similarity) Bias
•If premises and conclusions are similar -> valid
•If premises and conclusions dissimilar -> invalid
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