Averaged auditory evoked potentials (AEP) waveforms over the subjects to each vowel sound.

AEPs were recorded on the right and left anterior auditory fields (AAFs). Overall, the neural responses were elicited 0.2–0.4 s after the sounds stimulus onset and showed different peak latencies and amplitudes depending on the vowel stimulus. The AEPs recorded on both AAFs were generally similar. The bold lines represent the averaged AEP waveforms, and the shaded areas represent the standard deviation.