Wason selection task
a reasoning task involving four cards, each with a letter on one side and a number on the other, and a rule supposedly governing their correlation (e.g., if the letter is a vowel, then the number is even). One side of each card is shown (e.g., the cards might show E D 3 8), and the solver is asked which cards must be turned over to determine if the rule has been followed. Most participants demonstrate a confirmation bias, failing to check those instances in which the rule could have been breached (e.g., by turning over E and 3). Also called four-card problem. [developed in 1966 by Peter Cathcart Wason (1924–2003), British psychologist]