phases of corresponding signals were random (Rayleigh test, p>10−3). Thus, amplitudes of signals were variably positive or negative in different penetration sites, and they cancelled one another when combined. Second, at a fixed timing (24 ms), not all FB signals were at their peaks. In fact, mean phases of FB2 were near π/2 above and −π/2 below the inversion, that accounted for the signal amplitudes of FB2 tended to be near zero. To circumvent these phase sensitivities of signals, we also derived the distributions of the increments of FB power from the baseline (Fig. 6B). There were notches at the depth of inversion due to the fact that inversion reduces the amplitudes of signals in all FBs. Above that depth, the power in all FBs decreased gradually. However, at all depths, all FBs maintained significant (above zero) elevation in power (bootstrap, p<0.05). Thus, volume conduction occurs irrespective of frequency band.
