Distraction is a universal feature of human cognition, yet individuals differ markedly in their vulnerability to attentional lapses. While sustained attention failures have been extensively studied, the mechanisms driving distraction remain debated. Recent opportunity-cost and goal-competition theories propose that attention fails when alternative goals become more beneficial than the current one. Building on this framework, our team at the University of Chicago has developed the Switch Continuous Performance Task (Switch-CPT), a novel paradigm that increases competition between task goals. Using this task, we have shown that attentional lapses increase when goals compete, and that distraction is further amplified when an alternative goal is rewarded. The present project aims to extend these findings by examining whether opportunity cost can explain individual differences in distractibility, particularly in Attention-Deficit/Hyperactivity Disorder (ADHD). In Aim 1, we will test ADHD patients and matched healthy controls using the Switch-CPT while recording EEG, in collaboration with the University of Strasbourg/INSERM (France). In Aim 2, we will establish a sustainable US–EU research network by organizing an international conference on distractibility and mental health through the IIRP. Together, this project will advance the mechanistic understanding of distraction and foster long-term transatlantic collaboration in cognitive neuroscience.