Enhanced interaural separation improves spatial release from masking in bilateral bone conduction hearing

Objectives Bone conduction (BC) stimulation inherently produces low interaural separation due to cross-head transmission, which limits binaural benefits when BC stimulation is applied bilaterally. This study aimed to determine the improvement in binaural hearing from attenuation of BC cross-head transmission, as quantified by spatial release from masking (SRM), and to compare these outcomes with bilateral air-conduction (AC) stimulation. Methods Twenty normal-hearing adults participated. BC stimulation was simulated using AC headphones combined with an averaged cross-head transmission model representative of mastoid stimulation. Speech-in-noise performance was measured using the Swedish Matrix Test. SRM was calculated as the difference in speech reception thresholds between co-located speech and noise (S 0 N 0 ) and spatially separated condition (S 0 N 45 ). Four stimulation conditions were tested: AC stimulation, simulated BC with unattenuated cross-head transmission, and simulated BC with the same transmission attenuated by 5 dB and 10 dB. Results SRM increased systematically with increasing attenuation of BC cross-head transmission. Unattenuated BC stimulation produced the lowest SRM (mean 3.21 dB). Attenuation by 5 dB significantly improved SRM to 5.46 dB, while 10 dB attenuation further increased SRM to 6.47 dB. AC stimulation yielded the highest SRM (7.16 dB). SRM with 10 dB cross-head attenuation did not differ significantly from AC stimulation, whereas SRM with 5 dB cross-head attenuation remained significantly lower than AC. Conclusion Partial attenuation of BC cross-head transmission substantially improves binaural speech-in-noise performance. A reduction of 5 dB gives a meaningful binaural benefit, while a 10 dB reduction produces SRM comparable to bilateral AC stimulation. These findings indicate that robust attenuation, rather than precise cancellation, of BC cross-head transmission may be sufficient to enhance binaural hearing in bilateral BC applications.