The response to novel stimuli was characterized by the expected midline frontocentral P3 source, both in patient and control groups. However, CSD-PCA separated an additional source contributing to the midline novelty P3: the novelty vertex source (241), which was present only for novels, and was distinct from a later frontal source (343) having the same latency and topography as observed for targets. This source is evidenced in ERP waveforms as an inflection on the rising phase of the novelty P3 (cf. Figure 1, midline sites at latencies following nontarget P2) and accords well with findings by Yago, Escera, Alho, Giard, and Serra-Grabulosa (2003), who also reported an early central source “before the onset of the [novelty P3] waveform, contributing solely to its early phase” (p. 383).
