A primary reason the TF measures outperformed the time-domain P3 measure is that the time-region defined by the TF-PCA approach was more sensitive to differences due to externalizing. This stimulus-related activity was not apparent in the time-domain alone, and current time-domain measurement approaches offered no rational approach to selecting this window. In particular, approaches based on ranges of time or time-frequency activity (i.e. time-windows or TF regions of interest) are not data driven, and activity must be visually apparent or defined a priori. The most widely used time-domain data driven approach, PCA, generally produces separate measures for P2, N2, and P3 (see e.g. Chapman & McCrary, 1995; Dien et al., 2003; Spencer, Dien, & Donchin, 1999, 2001), rather than spanning that time range like the TF-PC3 from the current decomposition. The current results demonstrate that this new approach to ERP decomposition can extract time- and frequency-specific activity that is more sensitive to externalizing-related variance in the ERP than P3 peak amplitude, and offers support for the idea that TF-PCs from this approach may better represent processes relevant to these psychopathologies.
