Figure 4. Analysis of alpha amplitudes. (A) Lateralized event-related amplitude changes in the frequency range between 0–120 Hz for the grouped configurations observed at the parieto-occipital channels (PO3, PO4, PO7, PO8, O1, and O2). In the figure, cold colors depict a reduction in power. The figure shows the strong decrease in power at frequencies around 8-12 Hz (in the alpha band) during memory retention. (B) Lateralized alpha amplitude, plotted as a function of time for grouped (black), partially grouped (red), and ungrouped (gray) configurations. The dashed rectangle denotes the time window during memory retention (350–1300 ms). (C) Mean lateralized (contralateral-ipsilateral) alpha amplitudes as a function of object configuration during the memory-retention time window (350–1300 ms); higher negative values reflect more reduced contralateral alpha activity. Error bars denote the 95% (within-subject) confidence interval. Significant differences revealed by pairwise comparisons are indicated by asterisks; * p < .05.