Given prior evidence of P3a and/or P3b (e.g., Atkinson et al., 2012; Frommann et al., 2008) and alpha event-related desynchronization (Koh et al., 2011) abnormalities in CHR patients, we sought to study these time and time-frequency measures concurrently in a novelty oddball paradigm (Bruder et al., 2009). We employed a generic strategy for ERP analysis, which combines current source density (CSD) transformations of surface potentials with principal components analysis (PCA) to yield data-driven and physiologically-meaningful component estimates (e.g., Kayser & Tenke, 2003, 2006a, 2006b). This approach improves on conventional ERP analysis by obtaining unique ERP component measures that are independent of the EEG recording reference (cf. Kayser & Tenke, 2010), while also having an unambiguous polarity and sharper topography (Tenke & Kayser, 2012). This approach also addresses the spatial smearing of the EEG at scalp by volume conduction, which may lead to spurious EEG coherence (e.g., Fein et al., 1988; Guevara et al., 2005; Roach & Mathalon, 2008; Schiff, 2005), although these issues have an even wider impact on EEG spectral analysis (cf. Fig. 1 in Tenke & Kayser, 2005).
