Post-stimulus time-frequency regions of interest (TFROI) were selected based on visual inspection of the grand average TFRs for each of the stimulus types and at selected midline electrode sites of interest (MESOI), these being Fz, FCz, Cz, CPz and Pz. The absolute θ power was computed as the average power within the post-stimulus TFROI. A corresponding pre-stimulus TFROI was also defined, having the same frequency band as the post-stimulus TFROI, but with a time window preceding that of the stimulus onset. The average power within this pre-stimulus TFROI was utilized as a reference for comparing event-related changes in post-stimulus power, and is referred to as the reference θ power. The post-stimulus relative θ power is computed either as the relative percentage change of the θ power to the reference θ power i.e. Equation 1relθpower=absθpower−refθpowerrefθpower∗100or by calculating the log ratio of the absolute θ power to the reference θ power, i.e. Equation 2relθpower=log10(absθpowerrefθpower)Grand average topographical maps across groups were computed for each of the ERONPL θ power measures (reference, absolute and relative).
