The focus of the present study was on the novelty P3, which has a well-documented midline topography. Our reliance on CSD waveforms eliminates quantitative and statistical ambiguities caused by the choice of a recording reference, while sharpening and enhancing these midline topographies, thereby simplifying measurements and comparisons between groups. Moreover, the distinctive pattern of localized sources and sinks observed in the novelty oddball task indicate qualitative differences across conditions (cf. Figure 3b, factors 241, 343, and 542). For this reason, separate repeated measures analyses of variance (ANOVAs; BMDP-4V; Dixon, 1992) were conducted for the sources underlying the late positivities to targets and novels using subsets of electrode sites corresponding to these characteristic topographies. Greenhouse–Geisser ε correction was applied when appropriate (e.g., Keselman, 1998).
