In short, in the WCST, people have to classify cards according to different criteria. There are four different ways to classify each card, and the only feedback is whether the classification is correct or not. One can classify cards according to the color of its symbols, the shape of the symbols, or the number of the shapes on each card.
The classification rule changes every 10 cards, and this implies that once the participant has figured out the rule, the participant will start making one or more mistakes when the rule changes. The task measures how well people can adapt to the changing rules.