从近似到验证：重新思考人工耳蜗的频率匹配声学模型

文献信息

中文摘要

目的： 本研究旨在通过确定声码器是否能同时捕捉感知音质和言语表现，来验证其作为人工耳蜗声学模型的有效性。我们假设，有效的人工耳蜗声学模型需要输入滤波器与输出音调或噪声频带之间存在听者特定的频率失配量。
设计： 44名成人单侧聋人工耳蜗使用者在其初始刺激后的不同时间点接受了1至5次测试，共计73次测试。参与者在单耳植入人工耳蜗，对侧耳具有正常或接近正常的听力，从而允许进行受试者内比较。在实验1中，参与者使用调整法程序，通过调整三个参数来选择与其人工耳蜗最相似的声学模型：声学输出的低频和高频截止频率，以及通道间相互作用（输出声音载波之间的重叠）。在实验2中，参与者使用评估总体相似性和四个声学维度（可懂度、愉悦度、刺耳度和响度）的问卷，对五种声学模型类型的感知相似性进行评分。这五种模型类型包括：自我选择的模型、两种全通道频率匹配声码器（音调和噪声）以及两种六通道频率匹配声码器（音调和噪声）。频率匹配的声学模型其输出噪声频带或音调与分析滤波器频率匹配。在实验3中，在六种条件下评估言语感知：单独使用人工耳蜗，以及将五种声学模型类型分别呈现给正常听力耳。
结果： 几乎所有参与者（73次测试中的69次）选择的声学模型频率范围与其临床频率分配表不同。自我选择模型的低频边缘显著高于临床分配（Cochlear Ltd.为456 Hz，MED-EL为266 Hz）。超过80%的选择使用了最小的通道相互作用（音调、非重叠噪声频带或相邻噪声频带）。与所有频率匹配模型相比，自我选择模型获得了显著更高的相似性评分（平均6.11，其中6表示“有些相似”，7表示“非常相似”），而频率匹配模型的评分约为3（“不太相似”）。自我选择模型在多个声学维度上被评为与人工耳蜗最相似，并且是唯一在任何维度上与人工耳蜗评分无显著差异的模型。在言语感知方面，全通道频率匹配模型在单词和句子方面均显著高估了与人工耳蜗相比的表现。自我选择模型提供的言语得分最接近人工耳蜗的表现。对相似性评分和言语感知得分的联合分析表明，自我选择模型是唯一同时实现对人工耳蜗的感知相似性（评分为6.11，7为“非常相似”）和可比的言语感知得分（相差在五个百分点以内）的声学模型。
结论： 频率匹配的声学模型无法复制人工耳蜗的声音，而且全通道频率匹配的声学模型还显著高估了言语感知。相比之下，纳入听者特定感知频率失配的自我选择声学模型在主观音质和言语可懂度方面均提供了显著更好的匹配。然而，个体间相似性评分的变异性可能表明，当前参数集仍未涵盖其他感知成分。这些发现对频率匹配的人工耳蜗声学模型在研究应用中的有效性提出了质疑。

英文摘要

OBJECTIVES: This study aims to validate vocoders as acoustic models of cochlear implants by determining whether they capture both perceptual sound quality and speech performance. We hypothesize that valid acoustic models of cochlear implants require listener-specific amounts of frequency mismatch between input filters and output tones or noise bands.
DESIGN: Forty-four adult single-sided deaf cochlear implant users were tested 1 to 5 times for a total of 73 sessions at different time points after initial stimulation. Participants had a cochlear implant in one ear and normal or near-normal hearing in the contralateral ear, allowing within-subject comparisons. In Experiment 1, participants used a method-of-adjustment procedure to select acoustic models most similar to their cochlear implant by adjusting three parameters: low- and high-frequency cutoffs of the acoustic output, and channel interaction (overlap among output sound carriers). In Experiment 2, participants rated the perceptual similarity of five acoustic model types using questionnaires assessing overall similarity and four acoustic dimensions (intelligibility, pleasantness, harshness, and loudness). The five model types included the self-selected model, two all-channel frequency-matched vocoders (tone and noise), and two six-channel frequency-matched vocoders (tone and noise). Frequency-matched acoustic models had output noise bands or tones that were frequency-matched to the analysis filters. In Experiment 3, speech perception was evaluated under six conditions: with the cochlear implant alone and with each of the five acoustic model types presented to the normal hearing ear.
RESULTS: Nearly all participants (69 of 73 sessions) selected acoustic models with frequency ranges different from their clinical frequency allocation tables. The low-frequency edge of self-selected models was significantly higher than clinical allocations (456 Hz for Cochlear Ltd. and 266 Hz for MED-EL). Over 80% of selections used minimal channel interaction (tones, nonoverlapping noise bands, or adjacent noise bands). Self-selected models received significantly higher similarity ratings (mean of 6.11, where 6 means "somewhat similar" and 7 "very similar") compared with all frequency-matched models, which were rated around 3 ("not very similar"). Self-selected models were rated most similar to the cochlear implant across multiple acoustic dimensions and were the only models not rated significantly different from the cochlear implant on any dimension. For speech perception, all-channel frequency-matched models significantly overestimated performance compared with the cochlear implant for both words and sentences. Self-selected models provided speech scores closest to cochlear implant performance. Joint analysis of similarity ratings and speech perception scores demonstrated that self-selected models were the only acoustic models achieving both perceptual similarity to the cochlear implant (rating of 6.11 with 7 being "very similar") and comparable speech perception scores (within five percentage points).
CONCLUSIONS: Frequency-matched acoustic models fail to replicate the sound of a cochlear implant and all-channel frequency-matched acoustic models also significantly overestimate speech perception. In contrast, self-selected acoustic models incorporating listener-specific perceptual frequency mismatch provide substantially better matches in both subjective sound quality and speech intelligibility. However, variability in similarity ratings across individuals may suggest that additional perceptual components remain unaccounted for in the current parameter set. These findings question the validity of frequency-matched acoustic models of cochlear implants in research applications.