Electrophysiological Correlates of Binaural Interaction in Free Field Using Phase-Modulated Speech in Noise.

Purpose: This study investigated the applicability of speech-induced binaural beats (SBBs), a phase modulation procedure that can be applied to arbitrary speech signals to generate cortical auditory evoked potentials (CAEPs) as an objective marker of binaural interaction when presented dichotically, in a free-field environment. Furthermore, the effect of speech-shaped masking noise on CAEPs was investigated.

Method: Nineteen normal-hearing participants listened to sentences from a sentence matrix test. Sentences were presented from two loudspeakers situated 1 m away to the left and right of the participant. Each sentence contained one SBB and was presented in silence and in three different variations of masking noise: (a) identical noise from the same loudspeakers as the speech signals, (b) modified/phase-modulated noise from the same loudspeakers as the speech signals, and (c) noise presented from a separate loudspeaker placed behind the participants. Additionally, five participants listened to the sentences without noise, with and without one ear occluded, to ascertain the possibility of acoustic interference.

Results: CAEPs were successfully recorded in all participants, in the no noise condition and all noise conditions. The presentation of noise from a separate loudspeaker significantly reduced the N1 amplitude. No CAEPs were recorded when one ear was occluded, indicating no contribution of acoustic interference.

Conclusions: SBBs can be used to reliably evoke CAEPs as an objective marker of binaural interaction in the free field with masking noise. The advantage of this method is the use of speech material and the possible integration with existing behavioral tests for binaural interaction that utilize speech signals.

Supplemental material: https://doi.org/10.23641/asha.30063004.