Richardson Benjamin N, Kainerstorfer Jana M, Shinn-Cunningham Barbara G, Brown Christopher A
Neuroscience Institute, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA.
Department of Biomedical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA.
J Acoust Soc Am. 2025 Feb 1;157(2):1045-1056. doi: 10.1121/10.0034869.
Bilateral cochlear implant (BiCI) usage makes binaural benefits a possibility for implant users. Yet for BiCI users, limited access to interaural time difference (ITD) cues and reduced saliency of interaural level difference (ILD) cues restricts perceptual benefits of spatially separating a target from masker sounds. The present study explored whether magnifying ILD cues improves intelligibility of masked speech for BiCI listeners in a "symmetrical-masker" configuration, which ensures that neither ear benefits from a long-term positive target-to-masker ratio (TMR) due to naturally occurring ILD cues. ILD magnification estimates moment-to-moment ITDs in octave-wide frequency bands, and applies corresponding ILDs to the target-masker mixtures reaching the two ears at each specific time and frequency band. ILD magnification significantly improved intelligibility in two experiments: one with normal hearing (NH) listeners using vocoded stimuli and one with BiCI users. BiCI listeners showed no benefit of spatial separation between target and maskers with natural ILDs, even for the largest target-masker separation. Because ILD magnification relies on and manipulates only the mixed signals at each ear, the strategy never alters the monaural TMR in either ear at any time. Thus, the observed improvements to masked speech intelligibility come from binaural effects, likely from increased perceptual separation of the competing sources.
双侧人工耳蜗（BiCI）的使用使植入用户有可能获得双耳优势。然而，对于BiCI用户来说，耳间时间差（ITD）线索的获取有限以及耳间声级差（ILD）线索的显著性降低，限制了将目标声音与掩蔽声音在空间上分离所带来的感知优势。本研究探讨了在“对称掩蔽器”配置中，放大ILD线索是否能提高BiCI听众对掩蔽语音的可懂度，这种配置可确保由于自然存在的ILD线索，双耳都不会从长期的正向目标与掩蔽器比率（TMR）中获益。ILD放大估计八度宽频带内的即时ITD，并将相应的ILD应用于在每个特定时间和频带到达双耳的目标 - 掩蔽器混合信号。在两个实验中，ILD放大显著提高了可懂度：一个实验是让正常听力（NH）听众使用声码刺激，另一个实验是让BiCI用户参与。即使对于最大的目标 - 掩蔽器分离，BiCI听众在自然ILD情况下也未显示出目标与掩蔽器之间空间分离的优势。由于ILD放大仅依赖并操纵每只耳朵处的混合信号，该策略在任何时候都不会改变任何一只耳朵的单耳TMR。因此，观察到的掩蔽语音可懂度的提高来自双耳效应，可能是由于竞争声源的感知分离增加。
