The auditory GBR has been quantified with different methods, typically involving the transformation of the time-voltage domain EEG or event-related potential (ERP) signal into the time-frequency domain. Repeated applications of Fourier, Hilbert, or wavelet transformations produce time-frequency decompositions of EEG or ERP signals. Our analysis focuses on measures of total power, evoked power, and phase-locking factor (PLF), and typically these effects are fronto-centrally distributed across EEG channels. Total power (or event-related spectral perturbation (Delorme and Makeig, 2004) is a measure of the event-related change in power across individual trials, including both phase synchronous and asynchronous activity. Evoked power describes only phase-locked event-related changes in power because the time-frequency transformation is derived from the time-domain averaged ERP waveform. Finally, PLF (also called intertrial phase coherence (Delorme and Makeig, 2004) is a measure of phase consistency across trials from a single electrode or source.
