Cognitive and memory performance patterns associated with ADHD subtypes
This study investigated whether there were unique cognitive and memory patterns attributable to Attention Deficit Hyperactivity Disorder Combined or Inattentive subtypes (ADHD C or ADHD-I) or whether the patterns were common to ADHD regardless of subtype. Children ages 8-16 diagnosed with ADHD-C (n= 26) and children diagnosed with ADHD-I (n=30) formed the two clinical groups, and 31 non-clinical children served as control participants. The areas of neurocognitive functioning investigated included verbal working memory, verbal short-term memory, verbal organization and effort, sustained visual attention, and visual processing speed This study did not find verbal working deficits in the ADHD-C group using the WISC-III Arithmetic and Digit Span backwards portion of Digit Span as a working memory task. As predicted, no differences in short-term verbal memory were found, suggesting that children with ADHD regardless of subtype do not have difficulties with encoding verbally presented material. Children with ADHD did not evidence difficulties relative to controls on a CVLT-C learning task. However because the construct validity of the CVLT-C as a measure of executive function is unclear, the finding of no differences in verbal working memory performance across groups may reflect instrumentation error rather than reflect the true absence of group differences. The hypothesis that children with ADHD-C would evidence significantly more errors of commission, have elevated response risk-taking and less perceptual sensitivity to the task on the CCPT than children with ADHD-I and controls was not confirmed. While children with ADHD-C did have significantly fewer correct hits when compared with controls, their performance did not differ significantly from children with ADHD-I. Children with ADHD-I evidenced significantly more errors of omission and had significantly fewer correct hits compared with controls. A unique finding of this study was that severity of inattentive symptoms was significantly related to a restricted risk taking on the CCPT and poorer performance on the WISC-III Coding subtest. These results suggest that when diagnosing ADHD using behavioral checklists, it is important to consider symptom severity as well as the presence or absence of the behavioral symptoms.