Objective and Subjective Measures of Spatial Hearing in Unilateral Cochlear Implant Users with Bilateral Profound Hearing Loss

Abstract

Purpose: The ability to benefit from spatial separation between target and masker signals is important in multi-sound source listening environments. The goal of this study was to measure the spatial release from masking (SRM) in unilateral cochlear implant (CI) users with bilateral profound hearing loss. We also determined the relationships between the SRMs and the self-reported spatial hearing abilities.Methods: Fourteen unilateral CI users with bilateral profound hearing loss participated in this study. The target sentence was always presented to the front of the listener, and the nonfluctuating speech-shaped noise (SSN) or fluctuating speech noise was either co-located with the target (speech at 0°, noise at 0°, S0N0) or spatially separated at ± 90°. The SRM was quantified as the difference between speech recognition thresholds (SRTs) in the co-located and spatially separated conditions. The self-reported spatial hearing abilities were also measured using validated subjective questionnaires.Results: Overall, the SRTs were lower (better) with SSN than with fluctuating speech noise. When the noise was presented to the non-CI ear (speech at 0°, noise at non-CI ear, S0Nnonci), speech-in-noise recognition was the greatest due to head shadow or better-ear listening effect, resulting in the SRMs of approximately 5~6 dB regardless of noise type. When the noise was given to the CI ear (speech at 0°, noise at CI ear, S0Nci), some individuals exhibited positive SRMs (3~8 dB), while others showed negative SRMs, leading to little SRMs overall. When the SSN was given, subjects with less SRMs (less spatial separation benefits on the objective test) reported greater subjective spatial hearing difficulties.Conclusion: The spatial hearing of unilateral CI users varied by the position of the sound source. Listeners' spatial hearing abilities, which are unpredictable from clinical routine tests, need to be assessed by either objective or subjective measures.