Wisconsin Card Sort Test

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

Method
Initially, four stimulus cards are presented to the participant: the first has one red triangle, the second has two green stars, the third has three yellow crosses, and the fourth has four blue circles. He or she is then given a stack of additional cards and asked to match each one to one of the four stimulus cards, thereby forming four separate piles of cards. The participant is not told how to match the cards; however, he or she is told whether a particular match is right or wrong.

To determine whether each card is sorted correctly, a specific rule is chosen. A trial is correct if it is placed in the pile which matches the card on the dimension of the rule. If the participant successfully sorts a specific number of consecutive trials, the rule is changed. The task continues for 128 trials or until all rule changes have been accomplished successfully (called achieved categories).

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. Since the early 1990s, however, computerized versions of the task have been available, the most recent version being the windows-compatible version 4.0. 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 the following results:
 * Number of categories achieved
 * Number of trials
 * Number of errors
 * Number of perseverative errors
 * Percentage perseverative errors

Clinical use
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. 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. A more sophisticated description of deficits of this type is "executive dysfunction".

Use in research
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. The test's use in neurodegenerative diseases such as motor neurone disease and multiple sclerosis 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.