Wednesday, November 04, 2009 11/4/09 - cognitive misers

In today's excerpt - the human brain is a "cognitive
miser"- it can employ several approaches to solving a
given problem, but almost always chooses the one
that requires the least computational power:

"We tend to be cognitive misers. When approaching a
problem, we can choose from any of several cognitive
mechanisms. Some mechanisms have great
computational power, letting us solve many problems
with great accuracy, but they are slow, require much
concentration and can interfere with other cognitive
tasks. Others are comparatively low in computational
power, but they are fast, require little concentration
and do not interfere with other ongoing cognition.
Humans are cognitive misers because our basic
tendency is to default to the processing mechanisms
that require less computational effort, even if they are
less accurate.
Are you a cognitive miser? Consider the following
problem, taken from the work of Hector Levesque, a
computer scientist at the University of Toronto. Try to
answer it yourself before reading the solution.

Problem: Jack is looking at Anne, but Anne is looking
at George. Jack is married, but George is not. Is a
married person looking at an unmarried person?

A) Yes

B) No

C) Cannot be determined

"More than 80 percent of people choose C. But the
correct answer is A. Here is how to think it through
logically: Anne is the only person whose marital status
is unknown. You need to consider both possibilities,
either married or unmarried, to determine whether you
have enough information to draw a conclusion. If Anne
is married, the answer is A: she would be the married
person who is looking at an unmarried person
(George). If Anne is not married, the answer is still A:
in this case, Jack is the married person, and he is
looking at Anne, the unmarried person. This thought
process is called fully disjunctive reasoning -
reasoning that considers all possibilities. The fact that
the problem does not reveal whether Anne is or is not
married suggests to people that they do not have
enough information, and they make the easiest
inference (C) without thinking through all the
Most people can carry out fully disjunctive reasoning
when they are explicitly told that it is necessary (as
when there is no option like 'cannot be determined'
available). But most do not automatically do so, and
the tendency to do so is only weakly correlated with

"Here is another test of cognitive miserliness, as
described by Nobel Prize-winning psychologist Daniel
Kahneman and his colleague Shane Frederick.

"A bat and a ball cost $1.10 in total. The bat costs
$1.00 more than the ball. How much does the ball

"Many people give the first response that comes to
mind - 10 cents. But if they thought a little harder, they
would realize that this cannot be right: the bat would
then have to cost $1.10, for a total of $1.20. IQ is no
guarantee against this error. Kahneman and
Frederick found that large numbers of highly select
university students at the Massachusetts Institute of
Technology, Princeton and Harvard were cognitive
misers, just like the rest of us, when given this and
similar problems."

Keith E. Stanovich, "Rational and Irrational Thought:
The Thinking That IQ Tests Miss," Scientific American,
November/December 2009, pp. 35-36.


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