<p>Error monitoring is a critical cognitive function that enables the detection of deviations from intended goals and the initiation of corrective actions. Two influential theoretical frameworks propose distinct mechanisms underlying this process: conflict detection and reinforcement learning. The conflict detection account emphasizes the recognition of incompatible response tendencies, while reinforcement learning models focus on predicting error likelihood and updating expectations based on outcomes. Disentangling the contributions of these mechanisms remains challenging, as errors frequently involve both heightened response conflict and unexpected results. The present study aimed to differentiate these mechanisms using functional magnetic resonance imaging (fMRI) in the stop-signal task. Forty-four participants completed the task, during which response conflict intensity (reflected in stop-signal delay, SSD) and error expectancy (indexed by stop-response interval, SRI) were assessed. fMRI data were analyzed to investigate how these measures relate to neural activity associated with error processing. The results revealed that both SSD and SRI influenced post-error slowing. However, only SSD—reflecting response conflict—was significantly associated with error-related brain activity, particularly in the pre-supplementary motor area and superior frontal gyrus. These findings support the conflict detection theory, emphasizing the central role of response conflict in the neural mechanisms underlying inhibitory control failures.</p>