Figure 4.
A, Detection rate plotted as a function of prestimulus log-transformed α power quartiles revealing a significant decrease in target detection with increased power; *p < 0.05. B, Detection rate plotted as a function of opposite phases of prestimulus α phase, comparing high- and low-power trials. The effect of phase was only present for high power trials. **p < 0.005; n.s., not significant at α = 0.05; error bars represent within-subject SE. C, Circular histogram of the difference in mean phase of α activity between detected and undetected targets indicating a non-zero difference in phase. Distance from origin reflects the number of subjects whose difference vector falls within each phase quadrant, indicated by dashed gray lines. The blue arrow represents the average difference in mean phase across subjects. D, Two overlaid circular histograms of the mean phase of α activity preceding both detected (blue) and undetected (red) targets. Arrows represent the average phase of α across subjects for each condition. E, Results of a bootstrap analysis of the mean phase of α activity preceding detected and undetected targets. An equal number of trials were randomly sampled from each condition with replacement for each subject. The grand average phase of each of these samples was obtained for each condition and plotted on the chart. Vectors represent the mean across all bootstrapped samples. There is a clear separation of the mean phase of α between the two conditions, equating trial numbers. F, Grand average ERP at channel Pz in the 100 ms preceding and after the onset of the target. Note the opposite phase for the undetected (dashed) and detected (solid) targets. When collapsed across all targets, no phase-locking is apparent (gray).