Frequency compression in bimodal CI users (Sharma et al., 2021)

Purpose: Speech understanding in noise and horizontal sound localization is poor in most cochlear implant (CI) users with a hearing aid (bimodal stimulation). This study investigated the effect of static and less-extreme adaptive frequency compression in hearing aids on spatial hearing. By means of frequency compression, we aimed to restore high-frequency audibility, and thus improve sound localization and spatial speech recognition.Method: Sound-detection thresholds, sound localization, and spatial speech recognition were measured in eight bimodal CI users, with and without frequency compression. We tested two compression algorithms: a static algorithm, which compressed frequencies beyond the compression knee point (160 or 480 Hz), and an adaptive algorithm, which aimed to compress only consonants leaving vowels unaffected (adaptive knee-point frequencies from 736 to 2946 Hz).Results: Compression yielded a strong audibility benefit (high-frequency thresholds improved by 40 and 24 dB for static and adaptive compression, respectively), no meaningful improvement in localization performance (errors remained > 30 deg), and spatial speech recognition across all participants. Localization biases without compression (toward the hearing-aid and implant side for low- and high-frequency sounds, respectively) disappeared or reversed with compression. The audibility benefits provided to each bimodal user partially explained any individual improvements in localization performance; shifts in bias; and, for six out of eight participants, benefits in spatial speech recognition.Conclusions: We speculate that limiting factors such as a persistent hearing asymmetry and mismatch in spectral overlap prevent compression in bimodal users from improving sound localization. Therefore, the benefit in spatial release from masking by compression is likely due to a shift of attention to the ear with the better signal-to-noise ratio facilitated by compression, rather than an improved spatial selectivity.Supplemental Material S1. Individual audibility benefit (dB) for static and adaptive frequency compression and for different sound types. LP = low-pass; HP = high-pass; BB = broadband.Supplemental Material S2. Individual RMSE (deg) for sound localization with (static, adaptive) and without (no) frequency compression and for different sound types. LP = low-pass; HP = high-pass; BB = broadband.Supplemental Material S3. Speech recognition thresholds (dB) for S0N0 condition with and without frequency compression and the corresponding spatial release from masking [SRM (dB)] for each participant. Sharma, S., Nogueira, W., van Opstal, A. J., Chalupper, J., Mens, L. H. M., & van Wanrooij, M. M. (2021). Amount of frequency compression in bimodal cochlear implant users is a poor predictor for audibility and spatial hearing. Journal of Speech, Language, and Hearing Research. Advance online publication. https://doi.org/10.1044/2021_JSLHR-20-00653

目的：在大多数植入式耳蜗（CI）使用者中，配戴助听器（双模刺激）的用户在噪声中的语音理解和水平声源定位能力较差。本研究旨在探讨助听器中静态及较非极端的自适应频率压缩对空间听觉的影响。通过频率压缩，我们旨在恢复高频可听度，从而改善声源定位和空间语音识别。方法：对八位双模CI用户进行了声音检测阈值、声源定位和空间语音识别的测量，包括是否进行频率压缩。我们测试了两种压缩算法：一种为静态算法，该算法压缩超过压缩拐点（160或480 Hz）的频率；另一种为自适应算法，旨在仅压缩辅音而保留元音不受影响（自适应拐点频率从736到2946 Hz）。结果：压缩带来了显著的听觉益处（静态和自适应压缩分别使高频阈值提高了40和24 dB），在定位性能上没有明显的改善（错误率仍大于30度），以及所有参与者的空间语音识别。无压缩时的定位偏差（对于低频和高频声音分别指向助听器和植入侧）在压缩后消失或逆转。每位双模用户获得的听觉益处部分解释了任何个体在定位性能上的改善；偏差的变化；以及八位参与者中的六位在空间语音识别上的益处。结论：我们推测，诸如持续的听觉不对称和频谱重叠不匹配等限制因素阻止了双模用户通过压缩改善声源定位。因此，压缩在空间释放掩蔽方面的益处可能源于压缩通过改善信噪比而促进的注意力转向信号较好的耳朵，而不是空间选择性的改善。补充材料S1. 静态和自适应频率压缩以及不同声音类型的个人可听度益处（dB）。LP = 低通；HP = 高通；BB = 宽带。补充材料S2. 带有（静态、自适应）和未带有（无）频率压缩的声音定位的个人均方根误差（度）以及不同声音类型。LP = 低通；HP = 高通；BB = 宽带。补充材料S3. S0N0条件下的语音识别阈值（dB）以及带有和未带有频率压缩的对应的空间释放掩蔽[SRM（dB）]对于每位参与者。Sharma, S., Nogueira, W., van Opstal, A. J., Chalupper, J., Mens, L. H. M., & van Wanrooij, M. M. (2021). 双模耳蜗植入用户中频率压缩的量对听觉和空间听觉的预测能力较差。言语、语言和听力研究杂志。在线预发布。https://doi.org/10.1044/2021_JSLHR-20-00653