Department of Hearing and Speech Sciences, University of Maryland, College Park, Maryland 20742, USA.
National Military Audiology and Speech Pathology Center, Walter Reed National Military Medical Center, Bethesda, Maryland 20889, USA.
J Acoust Soc Am. 2022 Aug;152(2):1230. doi: 10.1121/10.0013746.
Bilateral cochlear-implant (BICI) listeners obtain less spatial release from masking (SRM; speech-recognition improvement for spatially separated vs co-located conditions) than normal-hearing (NH) listeners, especially for symmetrically placed maskers that produce similar long-term target-to-masker ratios at the two ears. Two experiments examined possible causes of this deficit, including limited better-ear glimpsing (using speech information from the more advantageous ear in each time-frequency unit), limited binaural unmasking (using interaural differences to improve signal-in-noise detection), or limited spectral resolution. Listeners had NH (presented with unprocessed or vocoded stimuli) or BICIs. Experiment 1 compared natural symmetric maskers, idealized monaural better-ear masker (IMBM) stimuli that automatically performed better-ear glimpsing, and hybrid stimuli that added worse-ear information, potentially restoring binaural cues. BICI and NH-vocoded SRM was comparable to NH-unprocessed SRM for idealized stimuli but was 14%-22% lower for symmetric stimuli, suggesting limited better-ear glimpsing ability. Hybrid stimuli improved SRM for NH-unprocessed listeners but degraded SRM for BICI and NH-vocoded listeners, suggesting they experienced across-ear interference instead of binaural unmasking. In experiment 2, increasing the number of vocoder channels did not change NH-vocoded SRM. BICI SRM deficits likely reflect a combination of across-ear interference, limited better-ear glimpsing, and poorer binaural unmasking that stems from cochlear-implant-processing limitations other than reduced spectral resolution.
双侧人工耳蜗植入（BICI）使用者获得的空间掩蔽释放（SRM；空间分离与共位条件下的语音识别改善）比正常听力（NH）使用者少，尤其是对于对称放置的掩蔽器，这些掩蔽器在双耳产生相似的长期目标与掩蔽器比。两项实验研究了这种缺陷的可能原因，包括有限的更佳耳瞥见（在每个时频单元中使用来自更有利耳的语音信息）、有限的双耳掩蔽（利用双耳差异来改善信号噪声检测）或有限的频谱分辨率。听者具有 NH（呈现未经处理或编码的刺激）或 BICI。实验 1 比较了自然对称掩蔽器、理想化的单耳更佳耳掩蔽器（IMBM）刺激，这些刺激自动进行更佳耳瞥见，以及添加较差耳信息的混合刺激，可能恢复双耳线索。对于理想化的刺激，BICI 和 NH 编码的 SRM 与 NH 未处理的 SRM 相当，但对于对称的刺激，SRM 低 14%-22%，表明更佳耳瞥见能力有限。混合刺激提高了 NH 未经处理的听者的 SRM，但降低了 BICI 和 NH 编码的听者的 SRM，表明他们经历了跨耳干扰而不是双耳掩蔽。在实验 2 中，增加声码器通道的数量并没有改变 NH 编码的 SRM。BICI 的 SRM 缺陷可能反映了跨耳干扰、有限的更佳耳瞥见以及较差的双耳掩蔽的结合，这源于除了频谱分辨率降低之外的人工耳蜗处理限制。
