Also known as the Wisconsin Card Sorting Task, the WCST is quick and easy to administer, requiring no specialized equipment but the deck of cards itself and a book to compare scores to. It's used to determine competence with abstract reasoning, and ability to change problem solving strategies when needed. Since those abilities are primarily determined by the frontal lobe, the WCST is often used in cases of possible brain damage to determine if there are problems with that area.

A WCST deck is made up of 128 response cards, and 4 stimulus cards. Each stimulus card has a different number, color, and shape of symbol: a red triangle, two green stars, three yellow crosses, and four blue circles. The response cards each have a different combination of those parameters, one has four red crosses, another has two yellow circles, and so forth. At the beginning of the test, the experimenter places the four stimulus cards on the table, and tells the subject that he is to sort the cards in the response deck on to each pile. This is purposefully ambiguous in order to make sure the subject will make incorrect placements, making it possible to tell how well the subject is picking up sorting rules during the game. The subject is also warned that the rules of sorting will change during the experiment.

From then on the experimenter answers only "right" or "wrong" to each card placement by the subject. Since there are only three possible characteristics to judge by (number, color, and shape), the experimenter can only change sorting rules twice. With each change of sorting rule, the experimenter watches to see how long it takes the subject to figure out the rules have changed, how long it takes him to learn the new rules, and what mistakes he makes while learning them.

With severe frontal and prefrontal cortex damage, the subject will actually get stuck in one sorting modality, and be unable to sort the cards any other way than by the first rule, no matter how many times they're told the placement is wrong. ADHD sufferers tend to have this same problem (known as perseveration) to a much lesser degree.

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