Experimental Oto-rhino-laryngology, Department of Neurosciences, KU Leuven, University of Leuven, Belgium.
Ear Hear. 2019 May/Jun;40(3):545-554. doi: 10.1097/AUD.0000000000000660.
To establish a framework to unambiguously define and relate the different spatial effects in speech understanding: head shadow, redundancy, squelch, spatial release from masking (SRM), and so on. Next, to investigate the contribution of interaural time and level differences to these spatial effects in speech understanding and how this is influenced by the type of masking noise.
In our framework, SRM is uniquely characterized as a linear combination of head shadow, binaural redundancy, and binaural squelch. The latter two terms are combined into one binaural term, which we define as binaural contrast: a benefit of interaural differences. In this way, SRM is a simple sum of a monaural and a binaural term. We used the framework to quantify these spatial effects in 10 listeners with normal hearing. The participants performed speech intelligibility tasks in different spatial setups. We used head-related transfer functions to manipulate the presence of interaural time and level differences. We used three spectrally matched masker types: stationary speech-weighted noise, a competing talker, and speech-weighted noise that was modulated with the broadband temporal envelope of the competing talker.
We found that (1) binaural contrast was increased by interaural time differences, but reduced by interaural level differences, irrespective of masker type, and (2) large redundancy (the benefit of having identical information in two ears) could reduce binaural contrast and thus also reduce SRM.
Our framework yielded new insights in binaural processing in speech intelligibility. First, interaural level differences disturb speech intelligibility in realistic listening conditions. Therefore, to optimize speech intelligibility in hearing aids, it is more beneficial to improve monaural signal-to-noise ratios rather than to preserve interaural level differences. Second, although redundancy is mostly ignored when considering spatial hearing, it might explain reduced SRM in some cases.
建立一个框架，明确地定义和关联语音理解中的不同空间效应：头部阴影、冗余、抑制、空间掩蔽释放（SRM）等。接下来，研究双耳时间和水平差异对语音理解中这些空间效应的贡献，以及这如何受到掩蔽噪声类型的影响。
在我们的框架中，SRM 被独特地定义为头部阴影、双耳冗余和双耳抑制的线性组合。后两个术语被组合成一个双耳术语，我们将其定义为双耳对比：一种来自于双耳差异的益处。这样，SRM 是一个单耳和一个双耳术语的简单和。我们使用该框架来量化 10 名正常听力参与者在不同空间设置下的这些空间效应。参与者在不同的空间设置下完成语音可懂度任务。我们使用头相关传递函数来操纵双耳时间和水平差异的存在。我们使用了三种频谱匹配的掩蔽器类型：固定语音加权噪声、竞争说话者和调制有竞争说话者宽带时域包络的语音加权噪声。
我们发现：（1）无论掩蔽器类型如何，双耳对比都因双耳时间差异而增加，但因双耳水平差异而减少；（2）大冗余（双耳同时具有相同信息的益处）会降低双耳对比，从而也会降低 SRM。
我们的框架为语音理解中的双耳处理提供了新的见解。首先，在现实听力条件下，双耳水平差异会干扰语音可懂度。因此，为了优化助听器中的语音可懂度，改善单耳信噪比比保留双耳水平差异更有益。其次，尽管在考虑空间听觉时冗余通常被忽略，但它可能解释了某些情况下 SRM 的降低。
