PSYC 2650 Chapter Notes - Chapter 13: Confirmation Bias, Syllogism, Belief Bias

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Published on 14 Apr 2013
University of Guelph
PSYC 2650
Chapter 13
Reasoning: Thinking Through the Implications of What
You Know
- Deduction: a process through which we start with claims or assertions that
we count as “given” and ask what follows from these premises
o Prediction based on our beliefs
- If we make deduction based on our beliefs then we turn out to be wrong, that
tells us that something is wrong with our beliefs
Confirmation and Disconfirmation
Confirmation Bias
- a strong tendency to seek out confirming evidence and to rely on that
evidence to make conclusions
- people are far more likely to seek our information that reinforces their belief
- when disconfirming evidence is found people tend to fail to use them in
adjusting their beliefs
- when people find confirming evidence they take it at face value
Memory for Disconfirming Evidence
- people accept confirming information at face value
- Gilovich
o People place bets on football teams
o When they loose they insist that they were right in picking the right
team but due to a fluke they lost
o And when people win they were in correcting the right team too
o Gamblers maintain their views despite the (seemingly) contrary
evidence provided by their own empty wallets
Belief Preservance
- even when disconcerting evidence is undeniable and in plain view sometimes
people don’t use it this is reffered to as belief preservance
- L. Ross, Lepper
o People were given suicide notes to read some were taken from the
police and some were written by college students (fake)
o Decide whether they were real or not
o People who were told they were right continued to think that their
social sensitivity was above average
o Those who were told they were wrong preserved their beliefs
o They search through their memory seeking information to confirm
that they have good social sensitivity
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Reasoning about Syllogisms
- Categorical syllogisms: are a type of logical argument that begins with two
assertions (the problems premises) each containing a statement about a
- Valid arguments (valid syllogisms)
- invalid syllogism
All P are M
All S are M
Therefore, all S are P
- This is invalid, to see this we must think about it in a different way
- All Plumbers are Mortal, All Sadists are Mortal, Therefore all Sadists are
- People who are asked to reason about syllogisms do quite poorly
Sources of Logical Errors
- Belief bias: if a syllogism’s conclusion happens to be something people
believe is true already, they are more likely to judge the conclusion as
following logically from the premises
- If the conclusion happens to be something they already thought was false
they easily reject the conclusion
The Four-Card Task
- Wason’s four card task
- People are shown a set of 4 cards (A,6,J,7)
- They are told if one card has a vowel on one side, it must have an even
number on the other, which cards must be turned over to put this rule to the
- Most people choose the A and the 6
- However the correct answer was to turn over the A and the 7
The Effects of Problem Content
- Performance is much better in some variations of the four-card task
- Griggs and Cox
o “If a person is drinking beer then the person must be over 19
o There were four cards again (Drinking a beer, 16, 22, Drinking a coke)
o People did much better on this task by selecting “Drinking a beer and
- This describes the rule of thought
- It seems then that the way we think depends on what we’re thinking about
Detecting Cheaters
- Our ancestors needed to reason in terms of betrayal and reason
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