Abstract
Inhibitory control challenges have long been theorized to underlie deficits in ADHD, but the precise mechanism(s) have remained unclear. Recent research using “forced-response” conflict tasks and computational modeling, capable of distinguishing the time-dependent contributions of habitual and goal-directed response preparation, has provided evidence that supports the idea that delayed goal-directed processing underlies inhibitory control challenges in adult ADHD. Still, it remains unclear how habitual and goal-directed responding adjust with increased (or decreased) interference that requires more (or less) inhibitory control, which matters because daily life involves varying levels of interference. To address this gap, we recruited adults meeting criteria for ADHD to complete a forced-response version of the arrow flanker task. We created circumstances of increased and decreased interference by manipulating the size of target and non-target (distractor) stimuli relative to each other. We utilized a crossover design, in which participants completed the arrow-flanker once while medicated and once while unmedicated (counterbalanced). Results showed that goal-directed responses were prepared more slowly for participants when unmedicated, regardless of interference circumstance. We directly tested the interaction between medication and interference, and the presence of medication did not especially help in one interference circumstance over the other. These findings add to a growing body of literature working toward better understanding the nature of inhibitory control within adult-ADHD.