Thinking and Deciding

90 LOGIC
before they were forced to this realization. No subject ended up selecting all of the
black shapes. 4
Resistance to instruction
Although subjects can be helped, there is also considerable evidence of resistance
to instruction. Possibly this resistance is a result of subjects’ biased commitment to
their initial answers. They ignore evidence against them because they want them to
be correct. (A way to test this would be to give the instruction before the subject
gives any answer; this has apparently not been tried.) For example, Wason (1977)
reports an experiment in which subjects were faced with clear evidence that they had
made an error, yet the subjects persisted in holding to their initial answer.
In the experiment, each card contained a circle or nothing in the middle, and a
border or nothing around the edge. The rule to be evaluated was this: “Every card
with a circle on it has a border around it.” Subjects were shown the following four
cards:
1. Circle in middle, edge covered up
2. No circle in middle, edge covered up
3. Border around edge, middle covered up
4. No border around edge, middle covered up
The question is to decide which cards must be uncovered in order to test the rule. The
right answer here is cards 1 and 4. Card 4 must be looked at because the rule would
be false if there were a circle. At a critical point in the experiment, the border of card
4 is uncovered, and the subject sees that the card has a circle in the middle. Here
is an example of what one subject, an undergraduate taking advanced mathematics,
who had chosen cards 1 and 3, said to the experimenter about her choice:
Experimenter: Can you say anything about the truth or falsity of the rule
from this card [card 4, with the cover removed, revealing a circle]?
Subject: It tells me [the rule] is false.
E: Are you still happy about the choice of cards you needed to see?
S: Yes.
E: Well, you just said this one makes it false.
S: Well, it hasn’t got a . . . border on it, so it doesn’t matter.
Several other subjects continued to deny that card 4 was relevant, even after they had
admitted that it actually proved the rule false when it was uncovered. Apparently
4 An alternative account of the effect of cutting down the problem to two kinds of cards and of spreading
it out over several trials is that these changes decrease the load on working memory. The problem as
originally presented may simply be too complex to be thought about all at once. An argument against this
account is that there is nothing to stop subjects from trying to overcome such memory limits by doing
for themselves what the experimenters do for them, that is, thinking about cards one by one. In general,
the limits imposed by working memory can be overcome by the use of more time-consuming strategies.
Therefore, although performance might improve if working memory were larger, it might also improve if
subjects simply thought more.