A number of investigators has also compared the ERN to a negative deflection in the stimulus-locked ERP: the N2 peaks between 200–400 msec after stimulus presentation, and thus generally occurs prior to the execution of a response. It is most pronounced on trials with high response conflict, and is evident in the incongruent minus congruent stimulus-locked difference waveform on correct trials. For example, in the Flankers task, high response conflict occurs when the flanking arrows are in the opposite direction as the center arrow (< < > < <). The N2 is thought to reflect the coactivation of the correct and incorrect response on correct trials (Falkenstein, Hoormann, & Hohnsbein, 1999; Yeung et al., 2004). Some source localization studies show that the N2 and the ERN have similar scalp topographies and a common neural source (caudal ACC), but they occur at different times relative to the response. That is, N2 occurs prior to correct responses and the ERN occurs following erroneous responses (Carter et al., 1998; van Veen & Carter, 2002; van Veen, Cohen, Botvinick, Stenger, & Carter, 2001; van
