Interference Pattern Caused by Bilateral Bone Conduction Stimulation Impairs Sound Localization

While bilateral fitting of bone conduction hearing devices (BCHDs) enhances spatial hearing, further improvements are constrained by the unresolved effects of crosstalk - an influential factor that disrupts binaural acoustic cues, such as interaural level difference (ILD) and interaural phase differences (IPD), essential for accurate sound localization. This paper introduces a simplified theoretical model to describe the crosstalk phenomenon and predict the cochlear vibrational responses under bilateral bone conduction (BC) based on principles of wave interference and superposition. The model reveals sound lateralization patterns across different ILD and IPD combinations, different from well-established principles governing air conduction (AC) sound localization, including the precedence effect and intensity rule. These predicted patterns are experimentally validated through cadaveric vibration measurements and are further corroborated in psychoacoustic sound lateralization tests conducted on healthy volunteers. The findings suggest that crosstalk induces wave interference in the skull and leads to the superposition of bilateral signals at the cochleae, resulting in these atypical lateralization patterns. This evidence highlights the inherent challenges of sound localization under BC compared to AC, identifying crosstalk-induced wave interference as a primary obstacle to improved spatial hearing for bilateral BCHD users.