When participants make errors in these speeded response tasks, an ERP component, the error-related negativity (ERN)1, presents as a negative deflection approximately 50–100 ms following the erroneous response (Falkenstein, Hohnsbein, Hoormann, & Blanke, 1991; W.J. Gehring, Goss, Coles, Meyer, & Donchin, 1993). Typical response-locked ERPs for error and correct trials are presented in Figure 1a. The ERN has been observed across tasks that employ a variety of stimulus and response modalities (Bernstein, Scheffers, & Coles, 1995; Holroyd, Dien, & Coles, 1998; Van’t Ent & Apkarian, 1999) and task difficulty (Band & Kok, 2000; Mathalon et al., 2003; Mathewson, Dywan, & Segalowitz, 2005; Moser, Hajcak, & Simons, 2005; Themanson, Hillman, & Curtin, 2006). The ERN is typically measured at midline frontal or central sites where the ERN is largest (i.e., FCz); Figure 1b presents the typical scalp distribution of the ERN. It is hypothesized that the anterior cingulate cortex (ACC) is the generator of the ERN as evidenced by studies using source localization (Dehaene, Posner, & Tucker, 1994; Holroyd et al., 1998; van Veen & Carter, 2002), magnetoencephalography (W. H. Miltner
