Memory for Action Rules and Reaction Time Variability in Attention-Deficit/Hyperactivity Disorder

Background Patients with attention-deficit/hyperactivity disorder (ADHD) exhibit increased reaction time (RT) variability. This finding is consistent across various choice RT tasks and is considered a core ADHD phenotype, often interpreted as expressing occasional attention lapses. This study explores the selective contribution of perceptual and working memory (WM) processes to increased RT variability in ADHD. Methods Low and high WM demands were manipulated in a battery of choice RT tasks administered to two groups of college students (subjects with ADHD vs. healthy control subjects). Results Ex-Gaussian distribution fitting revealed an increased rate of exceptionally slow RTs (i.e., higher τ values) in subjects with ADHD under all conditions. These group differences interacted with WM demands, showing the largest group differences when WM processing was most demanding (η_p² =.32). Under demanding WM conditions, evidence accumulation modeling demonstrated that increased RT variability in ADHD is not associated with either momentary or constant deficits in perceptual processing of the target. Rather, results favored a model associating increased RT variability in ADHD with reduced rate of WM retrieval. Conclusions These results suggest a pivotal contribution for the retrieval of action rules from WM to increased RT variability in ADHD.