We used posterior alpha power, a putative marker of the strength of visual attention 91, 92, to evaluate the effects of age and exogenous stimulation on visual attention of the target stimuli presented in the task. Following single-trial spectral decomposition, we extracted, squared, and averaged the magnitude length of the complex number vectors, yielding a measure of intertrial total spectral power for a given frequency, time point, and electrode. Power values were baseline corrected (−200 to 0 ms prior to target onset) by calculating the relative signal change where Pcorrectedt,f=Pt,f−Pbaseline(f)/Pbaseline(f) for the individual frequencies. Analysis focused on alpha-band frequencies (8–14 Hz) during a conservatively broad temporal window (100 to 400 ms after target onset), collapsed across occipital and parietooccipital electrodes on memory blocks.
