We previously showed that, collapsed across lines, frontal N1a and N1b amplitudes increased as a function of the tone loudness. In general, frontal and parietal N1a and N1b amplitudes were greater when the noise tone was presented, compared to the rare and standard tones (Slawecki, et al., 2003). The present findings showed greater frontal theta and alpha/beta ERO energy in response to noise tones during the 0–50 ms and 50–350 ms time windows, compared to standard tones. PLI values in the 0–50 ms and 50–350 ms time windows were significantly higher in noise tones, compared to standard and rare tones. These findings suggest that an increase in phase locking and reduction in phase variability could be responsible for the larger N1a and N1b amplitudes in response to the noise tones.
