The contribution of working memory and inhibition to the executive functioning of children with attention deficit hyperactivity disorder and children with reading disability

Executive functioning refers to self-regulatory processes that are responsible for organization of behavior and complex problem-solving. New paradigms to explain the specific components of executive functioning have, as yet, limited research testing them. One such paradigm is that which views working memory and inhibition as necessary components of executive function and relates executive dysfunction to deficiencies in these processes. The purpose of the present study was to examine the contribution of working memory and inhibition to the executive functioning of children with ADHD and children with Reading Disability (RD). Additionally, group differences in performance and developmental trends were examined. A sample of children with a sole diagnosis of RD (N = 44) and a sole diagnosis of ADHD (N = 50) who ranged in age from six years, 0 months to 11 years, 11 months participated in the study. Stepwise Regression analyses showed working memory (as measured by a Digit Span Backward task) to be a significant predictor of task performance on the Wisconsin Card Sorting Test (WCST) and on the Controlled Oral Word Association test (COWA-FAS Version). However, inhibition (as measured by the number of commission errors on the Gordon Diagnostic System) failed to significantly predict performance on these measures. Furthermore, working memory and inhibition failed to contribute significantly to performance on the Tower of London. Between-subjects design 2 x 2 ANOVAs (Diagnosis x Age) found the RD group to perform significantly poorer than the ADHD group on COWA while the groups did not significantly differ on the WCST and TOL measures. Furthermore, both groups performed normally on the WCST measure but were notably impaired on the TOL. Developmental trends were supported as age-related gains in performance were evident within each of the executive function measures. However, when compared to normative peers, impaired performances by younger children on measures of TOL and COWA continued to be apparent in older children. No interaction effects between Diagnosis and Age were found. The theoretical notion that working memory and inhibition are required for effective executive functioning is clearly worth revisiting. Furthermore, the examination of additional diagnostic populations is warranted.