Spectral analysis can also be applied directly to the ERP waveforms to quantify the underlying oscillatory nature of these waveforms. The spectral decomposition of the phase-locked activity may reveal evoked oscillations, often in the theta and alpha bands. The study of evoked oscillations has led to the proposition of an oscillatory model in comparison to the classic evoked model of the ERP. While the evoked model ascribes ERP generation to the superposition of a series of transient post-synaptic responses of pyramidal neurons that are independent of ongoing EEG oscillations (Pfurtscheller and Lopes da Silva, 1999), the oscillatory model accounts for the ERP through (i) partial phase resetting of the ongoing oscillations, with amplitude enhancement occurring through trial averaging of the phase-locked oscillations or (ii) phase-dependent amplitude modulation within single trials (Basar-Eroglu et al., 1992; Fell et al., 2004; Gruber et al., 2005; Klimesch, 1999; Klimesch et al., 2004; Kolev et al., 1997; Makeig et al., 2002; Penny et al., 2002; Schurmann et al., 2001; Shah et al., 2004; Yordanova et al., 2003). Limitations in methodology often make it difficult to
