Department of Otolaryngology-Head and Neck Surgery, Medical University of South Carolina, Charleston, South Carolina 29425-5500, USA.
Ear Hear. 2009 Apr;30(2):203-18. doi: 10.1097/AUD.0b013e31819769c1.
To assess the extent to which hearing aids improve spatial benefit by restoring the availability of interaural difference cues, the benefit attributable to spatial separation of speech and babble with and without bilateral hearing aids was measured as a function of low-pass cutoff frequency.
Twenty-one older adults with sloping high-frequency hearing loss were provided commercially available bilateral hearing aids. After a 3 to 6 month acclimatization period, speech levels corresponding to 50% correct recognition of sentences from the Hearing in Noise Test (HINT) were measured in a 65-dB SPL babble, with speech and babble low-pass filtered at 1.8, 3.6, and 5.6 kHz. Sentences were always at 0 degrees azimuth, and babble was at either 0 degrees or 90 degrees . Speech and babble spectra for all conditions were digitally recorded using a probe microphone placed in each ear canal of each subject. Spectra and levels of speech and babble and unaided thresholds for narrowband noises were used to calculate the aided audibility index and provide predictions of unaided and aided thresholds for HINT sentences, hearing aid benefit, and spatial benefit for each cutoff frequency. In addition, subjects' willingness to tolerate background noise with and without amplification was measured in the spatially coincident and spatially separated conditions using the Acceptable Noise Level (ANL) procedure.
Thresholds for HINT sentences in babble and ANL improved significantly when aided and when speech and babble were spatially separated. Specifically, hearing aid benefit improved significantly as cutoff frequency increased from 1.8 to 3.6 kHz but only when speech and babble were spatially separated; likewise, spatial benefit improved significantly from 1.8 to 3.6 kHz but only in the aided condition. No further improvement in hearing aid or spatial benefit was observed when cutoff frequency was increased from 3.6 to 5.6 kHz, although improvement in hearing aid benefit was predicted.
Hearing aid benefit, although significant, was poorer than predicted, suggesting that these older adults with high-frequency hearing loss did not take full advantage of the increase in audible speech information provided by amplification. Hearing aid benefit was also limited because hearing aids for some subjects did not restore speech audibility across the full bandwidth of speech. Unaided and aided spatial benefit was significantly greater than predicted, and aided spatial benefit was greater than unaided. This suggests that these older adults were able to take advantage of interaural level and time difference cues to improve speech recognition in babble and that they benefited from these cues to a greater extent with than without bilateral hearing aids. Finally, in contrast to results of previous studies, ANL may vary for an individual depending on the listening condition.
评估助听器通过恢复耳间差异线索的可用性来提高空间增益的程度，测量了归因于言语和背景噪声的空间分离的益处，以及在有和没有双侧助听器的情况下，作为低频截止频率的函数。
21 名高频听力损失呈斜坡状的老年人配备了市售的双侧助听器。在适应期 3 至 6 个月后，在 65dB SPL 背景噪声中测量与听力噪声测试（HINT）中句子的 50%正确识别相对应的言语水平，言语和背景噪声在 1.8、3.6 和 5.6kHz 处进行低通滤波。句子始终位于 0 度方位角，背景噪声位于 0 度或 90 度。使用置于每个受试者耳道内的探针麦克风，对所有条件下的言语和背景噪声以及未助听的窄带噪声的频谱和水平进行数字记录。使用频谱和言语及背景噪声水平以及未助听的窄带噪声阈值，计算助听可听度指数，并提供对 HINT 句子的未助听和助听阈值、助听器增益和每个截止频率的空间增益的预测。此外，使用可接受噪声级（ANL）程序，在空间重合和空间分离条件下测量受试者在有和无放大时对背景噪声的容忍度。
在助听和言语及背景噪声空间分离时，HINT 句子在背景噪声中的阈值显著提高。具体来说，当截止频率从 1.8kHz 增加到 3.6kHz 时，助听器增益显著提高，但仅在言语和背景噪声空间分离时；同样，当截止频率从 1.8kHz 增加到 3.6kHz 时，空间增益显著提高，但仅在助听条件下。当截止频率从 3.6kHz 增加到 5.6kHz 时，助听器或空间增益没有进一步提高，尽管预测会有提高。
助听器增益虽然显著，但低于预测值，这表明这些高频听力损失的老年人并没有充分利用放大提供的可听言语信息的增加。助听器增益也受到限制，因为对于一些受试者，助听器并不能在整个言语带宽内恢复言语可听度。未助听和助听的空间增益明显大于预测值，且助听的空间增益大于未助听的。这表明，这些老年人能够利用耳间水平和时间差线索来提高背景噪声中的言语识别能力，并且他们从双侧助听器中受益程度大于单侧。最后，与先前研究的结果相反，ANL 可能因个体的听力状况而异。
