In this study, the authors aimed to examine 4 domains of executive functioning in adults with attention-deficit/hyperactivity disorder (ADHD)-namely interference control, concept shifting, verbal fluency, and verbal working memory. Four groups of participants were included: (a) adults diagnosed with ADHD (ADHD(-): n = 20), (b) adults diagnosed with both ADHD and 1 or more comorbid disorder(s) (ADHD(+): n = 22), (c) adults referred for ADHD because of ADHD symptomatology but not diagnosed as such (non-ADHD; n = 34), and (d) healthy controls (n = 136). ADHD-related deficits (independent of comorbidity) were revealed for concept shifting and verbal working memory. In addition. the ADHD(+) and non-ADHD groups displayed deficits in terms of general processing speed. Given that these deficits were not found in the ADHD(-) group, the authors contend that these deficits are likely attributable to comorbidity rather than ADHD itself. Contrary to the authors' expectations, these findings do not correspond with the cognitive subtype hypothesis.
Marchetta, N. D. J. M., Hurks, P. P. M., Krabbendam, L., & Jolles, J. (2008). Interference control, working memory, concept shifting, and verbal fluency in adults with attention-deficit/hyperactivity disorder (ADHD). Neuropsychology, 22(1), 74-84. https://doi.org/10.1037/0894-422.214.171.124