Figure 5.

Prestimulus alpha power and memory accuracy correlate with posterior visual ERPs. Potentials on sensors contralateral to the stimulus (highlighted in white on the topographies, bottom) correlated significantly with posterior contralateral 8–14 Hz power (calculated at the same sensors, 500 to 100 ms before stimulus onset) and with memory accuracy (−|x − θ|) 200 to 250 ms after stimulus onset (see regression time courses, middle). The time range (shaded blue and green boxes, top) when both variables correlated significantly with broadband EEG corresponds approximately to the time of the negative-going N1 potential. This indicates that higher alpha power, which showed a positive correlation (green line, middle), tended to decrease the (negative) amplitude of the EEG, whereas accuracy (blue line, middle) was higher when the ERP was more negative (as indicated by a negative correlation). Both correlations peaked over posterior parietal and occipital sensors (bottom). Shaded errors indicate SEM.