Basic and complex cognitive functions in Adult ADHD

Adults with ADHD frequently show deficits in both basic cognitive processes (processing speed, distractibility) and complex executive functions (working memory, planning, cognitive flexibility). While prior research suggests that complex cognitive impairments may be largely rooted in foundational deficits, the extent to which these basic processes account for executive dysfunction remains debated. This study aimed to replicate previous findings by testing whether basic cognitive deficits explain the variance in ADHD diagnosis when accounting for complex cognitive impairments.

The researchers compared 48 adults diagnosed with ADHD against 48 healthy controls. Basic functions were evaluated using the Vigilance and Sustained Attention Test (WAFV), measuring processing speed via reaction time and distractibility via omission errors and reaction time dispersion. Complex cognitive functions—including selective attention, planning, working memory, cognitive flexibility, verbal fluency, and verbal memory—were assessed through a variety of standardized neuropsychological tests. The team used hierarchical logistic regression to determine how much of the variance in ADHD diagnosis was explained by complex functions alone versus when basic functions were controlled for.

Patients with ADHD demonstrated significantly slower processing speed and higher rates of distractibility compared to controls. When complex cognitive functions were analyzed in isolation, they explained 25% of the variance in ADHD diagnosis. However, once basic cognitive functions were included in the model, the variance explained by complex functions dropped to 9%. This 64% reduction suggests that a substantial portion of what appears to be complex executive dysfunction in adults with ADHD is attributable to underlying, more foundational deficits in basic information processing.