An attempt to discriminate different types of executive functions in the Wisconsin Card Sorting Test.

This study examined the roles of the phonological working memory and the central executive in the Wisconsin Card Sorting Test by altering the materials and the procedure of the task and using a dual-task design, in which cognitive abilities of normal participants were manipulated by performance of the secondary tasks selectively taxing the phonological loop or the central executive. The present study used three novel versions of the Wisconsin Card Sorting Test, namely the WCST-4 stimuli, the WCST-12-stimuli, and the WCST-12-stimuli-box, in all of which the participants were given the exact sorting criterion. So the tasks did not involve processes such as maintenance of inferences about the sorting criterion which would require phonological memory load. However, the tasks were assumed to require the executive process of response inhibition. In the WCST-4-stimuli condition no change was made to the WCST materials. In the other two conditions, relying on the assumption that the three-dimensional nature of the cards triggers inappropriate responses, unidimensional stimulus cards were used instead of the four normal three-dimensional WCST stimulus cards. The difference between these two conditions was that, in the WCST-12-stimuli-box condition, boxes were used to conceal the response cards previously sorted. The results supported Dunbar and Sussman's (1995) argument that some executive processes in the Wisconsin Card Sorting Test require the use of phonological store, and the present design was able to differentiate the type of executive functions that do not involve the use of a phonological loop from the ones that do. In addition, the results concerning manipulations of the visual aspects of the Wisconsin Card Sorting Test suggest that the three-dimensional nature of the WCST stimulus cards leads to an increase in the number of inappropriate responses produced with the executive secondary task interference.