Figure 2.

Alpha Phase Locking for No-TMS Trials in Experiment 2

(A) Instantaneous EEG phase, time locked to sound onset, was computed with the Hilbert transform after applying a band-pass filter (8–14 Hz). Right panel shows the 10 Hz phase-locking topography, with the effect evident in sensors overlaying not only auditory but also highlighted parieto-occipital cortex. Left panel depicts 10 Hz phase-locking for highlighted parieto-occipital sensors, which was significant (p < 0.001) between 50 ms and 250 ms following auditory stimulus onset (shaded window).

(B) Preferred alpha phase at 100 ms delay. Circular statistics were used to estimate PH(100), the mean instantaneous phase at 100 ms post sound (the time of highest sound-induced enhancement of phosphene detection rate in experiment 1). The number of trials within ±10 degrees of PH(100) is shown at left against time since sound, with corresponding topography at right. Note that the fluctuation in number of trials showing preferred phase PH(100) peaks not only at 100 ms (by definition), but also at around ∼200 ms, with the resulting cyclical pattern closely resembling the periodicity of perceived phosphene rate shown in Figure 1, in terms of peak-to-peak interval and peak latencies (i.e., frequency and phase). The shaded windows highlight that PH(100) not only at 100 ms (±20 m) but also at 200 ms (±20) was significantly higher than baseline (BSL) or the 150 delay (±20ms), all ^∗p < 0.05 Bonferroni corrected.

(C) EEG-phosphene correlation for separate datasets from experiments 1 and 2 (same participants). Scatterplot with red points and red line shows that the number of no-TMS EEG trials showing a phase within PH(100) at 19 equally spaced time points in the window 30 ms to 300 ms (experiment 2) correlates with the corresponding phosphene rates (scored along right axis) from separate experiment 1 (Figure 1). Please note the baseline (no-sound) condition was not considered in this analysis, as a time window relative to sound onset cannot be set for the preferred-phase EEG measure without a sound. Scatterplot with black points and black line shows a similar correlation between phosphene perception rate on the TMS trials in experiment 2 (scored along left axis) and dynamics of preferred phase for no-TMS trials in the same experiment.