Veugen Lidwien C E, Hendrikse Maartje M E, van Wanrooij Marc M, Agterberg Martijn J H, Chalupper Josef, Mens Lucas H M, Snik Ad F M, John van Opstal A
Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, P.O. Box 9101, 6500 GL, Nijmegen, The Netherlands.
Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, P.O. Box 9101, 6500 GL, Nijmegen, The Netherlands; Department of Otorhinolaryngology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, The Netherlands.
Hear Res. 2016 Jun;336:72-82. doi: 10.1016/j.heares.2016.04.008. Epub 2016 May 10.
Interaural differences in sound arrival time (ITD) and in level (ILD) enable us to localize sounds in the horizontal plane, and can support source segregation and speech understanding in noisy environments. It is uncertain whether these cues are also available to hearing-impaired listeners who are bimodally fitted, i.e. with a cochlear implant (CI) and a contralateral hearing aid (HA). Here, we assessed sound localization behavior of fourteen bimodal listeners, all using the same Phonak HA and an Advanced Bionics CI processor, matched with respect to loudness growth. We aimed to determine the availability and contribution of binaural (ILDs, temporal fine structure and envelope ITDs) and monaural (loudness, spectral) cues to horizontal sound localization in bimodal listeners, by systematically varying the frequency band, level and envelope of the stimuli. The sound bandwidth had a strong effect on the localization bias of bimodal listeners, although localization performance was typically poor for all conditions. Responses could be systematically changed by adjusting the frequency range of the stimulus, or by simply switching the HA and CI on and off. Localization responses were largely biased to one side, typically the CI side for broadband and high-pass filtered sounds, and occasionally to the HA side for low-pass filtered sounds. HA-aided thresholds better than 45 dB HL in the frequency range of the stimulus appeared to be a prerequisite, but not a guarantee, for the ability to indicate sound source direction. We argue that bimodal sound localization is likely based on ILD cues, even at frequencies below 1500 Hz for which the natural ILDs are small. These cues are typically perturbed in bimodal listeners, leading to a biased localization percept of sounds. The high accuracy of some listeners could result from a combination of sufficient spectral overlap and loudness balance in bimodal hearing.
声音到达时间（ITD）和强度（ILD）的双耳差异使我们能够在水平面上定位声音，并有助于在嘈杂环境中进行声源分离和语音理解。对于双耳佩戴设备（即一侧佩戴人工耳蜗（CI），另一侧佩戴助听器（HA））的听力受损听众而言，这些线索是否同样可用尚不确定。在此，我们评估了14位双耳佩戴设备听众的声音定位行为，他们均使用相同的峰力助听器和先进生物电子公司的人工耳蜗处理器，且在响度增长方面相互匹配。我们旨在通过系统地改变刺激的频段、强度和包络，来确定双耳线索（强度差、时间精细结构和包络ITD）和单耳线索（响度、频谱）对双耳佩戴设备听众水平声音定位的可用性和贡献。声音带宽对双耳佩戴设备听众的定位偏差有很大影响，尽管在所有条件下定位表现通常都很差。通过调整刺激的频率范围，或简单地打开和关闭助听器和人工耳蜗，响应可以系统地改变。定位响应在很大程度上偏向一侧，对于宽带和高通滤波声音，通常偏向人工耳蜗一侧，而对于低通滤波声音，偶尔偏向助听器一侧。在刺激频率范围内，助听器辅助阈值优于45 dB HL似乎是指示声源方向能力的一个先决条件，但并非保证。我们认为，即使在自然ILD较小的1500 Hz以下频率，双耳声音定位可能也基于ILD线索。这些线索在双耳佩戴设备听众中通常会受到干扰，导致对声音的定位感知出现偏差。一些听众的高精度可能源于双耳听力中足够的频谱重叠和响度平衡。
