Date of Award
Master of Arts
Research indicates that executive functioning is a multidimensional construct in school-age children (Korkman, Kemp, & Kirk, 2001; Welsh & Pennington, 1988). Executive dysfunction is primarily associated with Attention-Deficit/Hyperactivity Disorder (ADHD; Barkley, 2003). This association is because of a `core' deficit in inhibitory control found in ADHD-Combined Type (ADHD-C; Barkley, 1997); however, inhibitory control is only one component of executive functioning. Children with dyslexia are thought to demonstrate a `core' deficit in phonological awareness (Wagner & Torgesen, 1987). However, little consideration is given to the potential executive deficits that may exist in children with dyslexia. Therefore, the purpose of the present study was to test for convergent and divergent executive functioning deficits in 8-to 12-year-old children with ADHD or dyslexia using a comprehensive battery of executive measures. On neuropsychological measures when intelligence (IQ) was used as a covariate, the ADHD group did not demonstrate divergent deficits while children with dyslexia had deficits in nonverbal fluency. No convergent deficits were found. When IQ was not used as a covariate, children with ADHD and dyslexia were found to have convergent deficits in nonverbal fluency and problem-solving. Furthermore, children with dyslexia had divergent deficits in processing speed and phonological short-term storage. On a behavioral rating measure (BRIEF) children with ADHD-C and Attention-Deficit/Hyperactivity Disorder-Predominantly Inattentive (ADHD-PI) had convergent deficits in behavioral regulation while children with ADHD-C, ADHD-PI, and dyslexia were all rated more poorly on a metacognitive factor compared to controls. An exploratory analysis was conducted to further understand convergent and divergent abilities on the Behavior Rating Inventory of Executive Functioning (BRIEF). Results indicated that ADHD-C and ADHD-PI shared deficits on the metacognitive subscales, but that ADHD-C demonstrated divergent deficits on subscales of behavioral regulation, particularly Inhibit, and on a Monitor subscale. Children with dyslexia were rated comparably to controls on all subscales of the BRIEF. Overall, it was found that executive deficits were not exclusive to ADHD. Rather, children with ADHD and dyslexia demonstrated convergent and divergent executive functioning deficits. The convergent deficits warrant further investigation as to whether they are a source of the comorbidity between dyslexia and ADHD. The limitations of the present study, recommendations for future directions, and clinical implications are discussed.
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