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The Wisconsin Card Sorting Test® (WCST) is a neuropsychological test of "set-shifting", i.e. the ability to display flexibility in the face of changing schedules of reinforcement.

Initially, a number of stimulus cards are presented to the participant. He or she is then given a stack of additional cards and asked to match each one to one of the stimulus cards, thereby forming separate piles of cards for each. The participant is not told how to match the cards; however, he or she is told whether a particular match is right or wrong.

The original WCST used paper cards and was carried out with the experimenter on one side of the desk facing the participant on the other.^[1] Since the early 1990s, however, computerized versions of the task have been available, the most recent version being the windows-compatible version 4.0.^[2] The latter has the advantage of automatically scoring the test, which was quite complex in the manual version. The test takes approximately 12-20 minutes to carry out and generates a number of psychometric scores, including numbers, percentages, and percentiles of: categories achieved, trials, errors, and perseverative errors.

Clinically, the test is widely used by psychiatrists, neurologists and neuropsychologists in patients with acquired brain injury, neurodegenerative disease, or mental illness such as schizophrenia. Although successful completion of the test relies upon a number of intact cognitive functions including attention, working memory, and visual processing, it is loosely termed a "frontal lobe" test on the basis that patients with any sort of frontal lobe lesion generally do poorly at the test. In particular, patients with lesions of the dorsolateral frontal lobe make a higher number of perseverative errors than control participants.^[3] Having achieved the first category they often continue to sort the cards according to the first rule long after that rule has been superseded. A recent factor analysis of the WCST has shown these perseverative errors to be the most useful outcome measure in assessing caseness.^[4] A more sophisticated description of deficits of this type is "executive dysfunction".

The WCST has been used in neuroimaging paradigms such as PET and MRI. As predicted by the acquired brain injury literature, completing the task involves activation primarily of the dorsolateral prefrontal cortex.^[5][6] The test's use in neurodegenerative diseases such as motor neurone disease has identified at least a subgroup of these patients for whom there is some subtle degree of cognitive dysfunction, in contrast to the traditional view that these were pure disorders of the motor system.

The test is also widely used in research into schizophrenia e.g.^[7][8]

• A free implementation of the Wisconsin Card Sorting Task is available as part of the PEBL Project.