Scalp topography of auditory evoked responses elicited by binaural beat illusions

Auditory binaural beat (BB) illusions are elicited when two sinusoidal sounds with slightly differing frequencies are presented separately to each ear. Neural processing of BBs can be explored using auditory evoked potentials (AEP). In this study BB AEP topography is investigated using eight bipolar channels with 9 electrodes (Fz, Cz, Pz, Oz, A1, A2, T3, T4 and Neck) and a ground placed on the forehead. Young adults with normal hearing were recorded with the BB paradigm using 400Hz, 50ms beats with a repetition rate of 1Hz. The Electroencephalogram (EEG) was acquired at 5Ksps and - references, Neck and Avg ((A2+A1)/2), were generated offline. Results demonstrated that while the Avg reference montage showed higher peak amplitudes for all electrodes, the A1 and A2 earlobe electrodes exhibited significant activity for the first BB peak (100ms) when referenced to the Neck. Additionally, the Neck reference revealed several differences between scalp regions: a maximum amplitude at Cz for the second peak (180ms), a polarity reversal for early peaks and substantial suppression of late peaks at T3 and T4. These results suggest lateral generators for the first BB peak and deep central/rostral generators for the late BB peaks.