A widely used test of abstract thinking, planning, and ability to alter mental set (2) as circumstances require. The test consists of 128 cards differing in colour, form, and number of design markings, and the respondent tries to match them to four target cards, the test administrator telling the respondent merely whether each sort is right or wrong but not what the rule is, and in the latter stages of the test the sorting rule is changed without warning, requiring the respondent to show flexibility. The test was developed at the University of Wisconsin by the US psychologist David A(lexander) Grant (1916–77) and Esta A. Berg and first published in the Journal of General Psychology in 1948. It is regarded as a good indicator of frontal lobe damage, and is especially useful for identifying perseveration (1, 2). WCST abbrev.