Drift diffusion analysis of the Stroop task reveals impaired adjustments of executive functions in ADHD patients

Background: Attention-deficit/hyperactivity disorder (ADHD) is commonly associated with executive dysfunction, yet traditional measures like mean reaction time (RT), accuracy, and reaction time variability (RTV) have shown limited sensitivity in capturing these deficits. Emotional dysregulation, a core symptom of ADHD, may influence executive control and behavioral adjustment, particularly in emotionally salient contexts. This study aimed to investigate cognitive adaptation in ADHD using both standard and computational analyses of Stroop task performance.Methods: Twenty-five adults with ADHD and 30 healthy controls completed a computerized Stroop task with neutral and emotional conditions. Each trial varied in congruency and was classified based on the congruency of the current and previous trial. Mean RT and RT variability were analyzed using linear mixed-effects models. To probe underlying cognitive mechanisms, Drift Diffusion Modelling (DDM) was applied to estimate drift rate, boundary separation, and non-decision time.Results: Standard analyses revealed significant Stroop and adaptation effects only in the emotional condition as the neutral condition did not induce the expected Stroop effect. Moreover, these analyses showed no group differences. In contrast, the DDM-analysis revealed robust group differences: ADHD patients showed lower drift rates (probability difference [PD] = 0.996), higher non-decision time (PD = 0.992), and reduced adaptation to conflict in all DDM parameters, particularly following incongruent trials (e.g., iC vs. cC drift rate difference: PD = 0.955) in the emotional Stroop.Conclusions: A DDM-analysis revealed that ADHD patients have impaired adaptation to cognitive conflict, particularly in emotionally salient contexts. These findings suggest that computational modelling may uncover executive dysfunctions in ADHD otherwise missed by conventional analysis.