Wisconsin Card Sorting test

n. A test of problem solving and ability to alter one's mental set, using 128 cards with geometric shapes in different colors and different numbers. On each trial the subject is asked to sort a card into one of four piles headed by an example card and is told only if the choice is wrong or right but not the rule which the tester has decided upon to determine correctness. After the subject makes 10 consecutive correct choices the principle of correctness is changed and the reactions of the subject observed.