Effects of response-set size on error-related brain activity.

To study the effect of response-set size on action monitoring processes, the error-related negativity (Ne/ERN), the correct-related negativity (Nc/CRN), and behavioral indicators of action monitoring were compared across three groups of participants performing a two-choice, a four-choice, or an eight-choice version of the flanker task. After controlling for differential contribution of stimulus-related activity to response-locked averages resulting from large differences in response times across conditions, response-set size had strong effects on Ne/ERN and Nc/CRN. With increasing response-set size, the Ne/ERN amplitude decreased, but the Nc/CRN amplitude increased. Moreover, post-error behavioral adjustments were impaired with an increasing response-set size. These results suggest that action monitoring severely suffers when response-set size is increased. Implications of these findings for present theories of Ne/ERN and Nc/CRN are discussed.