Based on the difference ERPs and the scalp distributions and timing of our EEG discriminating components, we believe we are tracking variation related primarily to the P2, N2, and P3 responses (Key et al., 2005), so we discuss our results partly in light of these. More specifically, our topographies are consistent with discrimination of the target-related P3b, frontal P3f, and post-motor potential (Pmp) subcomponents of the P3 (Makeig et al., 1999), as expected for our visual oddball task. Since amplitudes of these components are known to modulate with arousal and attention (Key et al., 2005; Luck et al., 2000; Nieuwenhuis et al., 2005), we use the classifier output (i.e. its decision certainty) to index the subjects’ attentional state (i.e. task engagement) during each trial. Our EEG-based fMRI regressors are thus revealing the BOLD correlates of modulations in task engagement.
