Gifford René H, Dorman Michael F, Brown Chris, Spahr Anthony J
Vanderbilt University, Department of Hearing and Speech Sciences, Nashville, TN 37232, U.S.A.
J Hear Sci. 2012 Dec;2(4):9-17.
In a previous paper we reported the frequency selectivity, temporal resolution, nonlinear cochlear processing, and speech recognition in quiet and in noise for 5 listeners with normal hearing (mean age 24.2 years) and 17 older listeners (mean age 68.5 years) with bilateral, mild sloping to profound sensory hearing loss (Gifford et al., 2007). Since that report, 2 additional participants with hearing loss completed experimentation for a total of 19 listeners. Of the 19 with hearing loss, 16 ultimately received a cochlear implant. The purpose of the current study was to provide information on the pre-operative psychophysical characteristics of low-frequency hearing and speech recognition abilities, and on the resultant postoperative speech recognition and associated benefit from cochlear implantation. The current data for the 16 listeners receiving cochlear implants demonstrate: 1) reduced or absent nonlinear cochlear processing at 500 Hz, 2) impaired frequency selectivity at 500 Hz, 3) normal temporal resolution at low modulation rates for a 500-Hz carrier, 4) poor speech recognition in a modulated background, and 5) highly variable speech recognition (from 0 to over 60% correct) for monosyllables in the bilaterally aided condition. As reported previously, measures of auditory function were not significantly correlated with pre- or post-operative speech recognition - with the exception of nonlinear cochlear processing and preoperative sentence recognition in quiet (=0.008) and at +10 dB SNR (=0.007). These correlations, however, were driven by the data obtained from two listeners who had the highest degree of nonlinearity and preoperative sentence recognition. All estimates of postoperative speech recognition performance were significantly higher than preoperative estimates for both the ear that was implanted (<0.001) as well as for the best-aided condition (<0.001). It can be concluded that older individuals with mild sloping to profound sensory hearing loss have very little to no residual nonlinear cochlear function, resulting in impaired frequency selectivity as well as poor speech recognition in modulated noise. These same individuals exhibit highly significant improvement in speech recognition in both quiet and noise following cochlear implantation. For older individuals with mild to profound sensorineural hearing loss who have difficulty in speech recognition with appropriately fitted hearing aids, there is little to lose in terms of psychoacoustic processing in the low-frequency region and much to gain with respect to speech recognition and overall communication benefit. These data further support the need to consider factors beyond the audiogram in determining cochlear implant candidacy, as older individuals with relatively good low-frequency hearing may exhibit vastly different speech perception abilities - illustrating the point that signal audibility is not a reliable predictor of performance on supra-threshold tasks such as speech recognition.
在之前的一篇论文中，我们报告了5名听力正常的听众（平均年龄24.2岁）以及17名年龄较大的听众（平均年龄68.5岁）的频率选择性、时间分辨率、耳蜗非线性处理，以及在安静环境和噪声环境下的言语识别情况。这17名年龄较大的听众患有双侧轻度至重度感音神经性听力损失（吉福德等人，2007年）。自该报告发表以来，又有2名听力损失患者完成了实验，使听力损失患者总数达到19名。在这19名听力损失患者中，有16名最终接受了人工耳蜗植入。本研究的目的是提供有关低频听力和言语识别能力的术前心理物理学特征，以及人工耳蜗植入术后的言语识别结果和相关益处的信息。目前这16名接受人工耳蜗植入的听众的数据表明：1）500赫兹时非线性耳蜗处理减少或缺失；2）500赫兹时频率选择性受损；3）对于500赫兹载波，低调制率下时间分辨率正常；4）在调制背景下言语识别能力差；5）在双侧助听条件下，单音节的言语识别高度可变（正确率从0到超过60%）。如先前报道，听觉功能测量与术前或术后言语识别没有显著相关性——除了非线性耳蜗处理以及安静环境（=0.008）和信噪比为+10分贝时（=0.007）的术前句子识别。然而，这些相关性是由两名具有最高非线性程度和术前句子识别能力的听众的数据驱动的。术后言语识别性能的所有估计值均显著高于植入耳（<0.001）以及最佳助听条件下（<0.001）的术前估计值。可以得出结论，患有轻度至重度感音神经性听力损失的老年人几乎没有或没有残余的耳蜗非线性功能，导致频率选择性受损以及在调制噪声中的言语识别能力差。这些人在人工耳蜗植入后，在安静环境和噪声环境下的言语识别都有非常显著的改善。对于那些佩戴合适的助听器仍难以进行言语识别的轻度至重度感音神经性听力损失的老年人来说，在低频区域的心理声学处理方面几乎没有损失，而在言语识别和整体交流益处方面却有很大收获。这些数据进一步支持了在确定人工耳蜗植入候选人时需要考虑听力图以外因素的观点，因为低频听力相对较好的老年人可能表现出截然不同的言语感知能力——这表明信号可听度并不是诸如言语识别等阈上任务表现的可靠预测指标。
