Match each bottom card to one of the four piles at the top. The correct rule is not explained — figure it out from feedback. After every 10 correct responses in a row, the rule changes without notice. This session has 64 trials. Use mouse / touch or keys 1–4 for piles left to right.
WCST forces you to infer a sorting rule from feedback, then adapt when the rule changes. Perseverative errors — sticking with an old rule — are the signature measure of cognitive flexibility in this classic paradigm.
Perseverative errors are incorrect sorts that would have been correct under the previous rule (after a rule change).