Human error monitoring during implicit and explicit learning of a sensorimotor sequence

During the acquisition of a sensorimotor sequence error monitoring as reflected by the error-related negativity (ERN) of the event-related brain potential was studied in normal human subjects. The central, imperative letter in an Eriksen-like flanker task either followed a repeating sequence or was determined randomly. 'Explicit learners' were informed about the presence of a sequence, whereas 'implicit learners' were not. Both groups learned the sequential structure inherent in the material as indicated by a speed-up in response time for structured compared to random trials. Most importantly, the ERN was larger for explicit compared to implicit learners. Thus, explicitly searching for a sequential regularity led to a more intensive engagement of the error monitoring system as reflected by the ERN.