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 the stimuli that evoke ERP components, like the P300, influence oscillatory changes within the dynamics of ongoing EEG rhythms (Basar-Eroglu and Basar, 1991; Demiralp et al., 2001a, 2001b; Karakas et al., 2000a, 2000b; Schurmann et al., 1995, 2001; Yordanova and Kolev, 1996;). This synchronization or enhancement of ongoing EEG oscillations by a time locked cognitive and/or sensory process is termed an event-related oscillation (ERO) (Basar et al., 2000; Begleiter and Porjesz, 2006; Roach and 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 with respect to their energy and phase relationships over a millisecond time scale with respect to task events.
