The early novelty source was preceded by an equally well-defined novelty N2 sink (179) at precisely the same sites that was not observed for targets. It is, therefore, this sink/source pair (i.e., 179/241) that best qualifies as a substrate for the response to novelty. To the extent that the novelty vertex source defines onset of the volume-conduced ERP at the midline, its differential engagement could contribute to, or even account for, the characteristic early onset of novelty P3, as well as its topographic shift with repetition (Friedman & Simpson, 1994). In contrast, the fact that the frontal P3 source for targets is comparable to that observed for novels precludes a unique role for this later frontal source in the automatic attentional response to novelty. To the contrary, the focal novelty vertex source suggests a more posterior generator (i.e., in or behind SMA),4 which is consistent with the localization of an equivalent dipole for go/no-go P3 in portions of cingulate cortex near motor areas (Verleger et al., 2006), and is a location more consistent with processes related to response inhibition than with task-specific stimulus classification or error processing per se.
