Wason Task studies provide some evidence to support the idea of two systems of processing, as described in the dual processing model of decision making. To recap, the dual processing model of decision making posits that we have two systems for processing information:

  1. System One: fast, automatic and intuitive
  2. System Two: slow, controlled and rational

In the Wason Task, participants are given a rule to test. The rule is stated as “if P, then Q.” You can see an example below:

Wason Selection Task
From Evans and Stanovich, 2013

Less than 10% of participants give the correct answer (Roth, 1979), which requires careful consideration of the rules and the problem (system two processing). Most people say A or A and 3. They use their intuition (system one processing) and don’t think through the problem rationally. They might select A and 3 since these are the numbers given in the problem itself. But if we think about the problem a bit more carefully we can see:

  • We need to turn over A to check the rule.
  • We don’t need to turn over D, since based on the rules given at the start we know that there must be a number on the other side.
  • We don’t need to turn over 3 since it doesn’t matter what is on the other side – even if it’s not an A, it still wouldn’t prove the rule wrong since the rule states if there’s an A on one side there’s a 3 on the other – there could be a 3 on one side and still have any letter on the other.
  • We need to turn over 7 because if there’s an A on the other side, the rule is proven wrong.

This study demonstrates that our decision making can be influenced by the system we use when processing information.


You can test your understanding of the Wason Task with this interactive video.


A note for IB Psych’ exam preparation

In the new syllabus for IB Psychology it’s most likely that you’ll be asked about “research related to…” thinking and decision making. It is therefore essential that you can explain how one or more studies are related to the dual processing model. The Wason Task studies give you cognitive studies to use, while the Iowa Gambling Task on vmPFC lesion patients gives you a biological connection with dual processing.