Processing speed and inhibitory control in children with ADHD and their relationship with the symptoms of ADHD

Attention Deficit/Hyperactivity Disorder (ADHD) is a prevalent neurodevelopmental disorder characterized by persistent patterns of inattention, hyperactivity, and impulsivity that impair functioning across multiple domains. While deficits in inhibitory control and processing speed are well-documented in ADHD, the precise neurocognitive mechanisms underlying these impairments and their specific relationships with ADHD symptom dimensions remain poorly understood. This study examined distinct profiles of processing speed and inhibitory control at the subcomponent level in 41 children with ADHD compared to 45 typically developing peers. Specifically, processing speed was dissociated into perceptual and verbal components, assessed via a visual recognition task (based on the theory of visual attention) and a rapid digit naming task, respectively. Inhibitory control was fractionated into response and interference inhibition, separately evaluated via go/no-go and flanker tasks. ADHD symptoms were assessed using the Swanson, Nolan, and Pelham rating scale IV. Results indicated that children with ADHD exhibited significantly lower verbal processing speed and impaired interference inhibition. Given significant correlations among these cognitive subcomponents and inattentive symptom, four mediation models were tested. Notably, only the model in which verbal processing speed mediated the relationship between interference inhibition and inattention was significant, suggesting that distinct cognitive deficits interact differentially to shape the clinical presentation of ADHD. These findings provide novel insights into the cognitive mechanisms underlying ADHD and have important implications for developing targeted cognitive interventions.