Are executive function tests dependent on working memory capacity?

The relationship between working memory (WM) capacity and three executive function tests, which were adopted from clinical neuropsychology, was studied. The subjects were normal 15-16-year-old students. A large set of WM measures included digit and word span, a modified memory-updating task, and five different complex WM span tasks. The complex span measures and the memory-updating task showed high intercorrelations. Of the three executive function tests, the Wisconsin Card Sorting Test (WCST) correlated significantly with WM tasks, the storage function of WM probably being a limiting factor in card sorting. The global performance measures of the WCST were more dependent on WM capacity than the number of perseverations. The two other executive function tests-the Tower of Hanoi and Goal Search Task-did not correlate with WM tasks. None of the executive function tests exhibited any significant intercorrelations. The results are in agreement with earlier studies, which have found separate executive functions. The present results and evidence from earlier studies suggest that there does not exist a unitary, limited-capacity central executive.