Event-related potentials (ERPs) are a series of negative and positive voltage deflections that are time locked typically to either sensory or cognitive events. They consist of several components that are averaged from the ongoing EEG that generally occur between 50 and 1000 msec. It has been suggested that certain ERP components, like the P300, are perhaps not the unitary emergent processes suggested by earlier authors; but that they may influence oscillatory changes within the dynamics of ongoing EEG rhythms (see: Basar-Eroglu & Basar, 1991; Schurmann et al., 1995, 2001; Yordanova & Kolev,1996; Karakas et al., 2000a, b; Demiralp et al., 2001). This synchronization or enhancement of ongoing EEG oscillations by a time locked cognitive and/or sensory process is termed an event-related oscillation (see Basar et al., 2000; Begleiter & Porjesz, 2006; Roach & Mathalon, 2008). EROs are thought to arise by a “phase re-ordering” of the background EEG in several frequency bands (Basar, 1980; Makeig et al., 2002). EROs are typically estimated by a decomposition of the EEG signal into phase and magnitude information for a range of frequencies and then changes in those frequencies are characterized over a millisecond time scale with respect to task events.
