Easwar Vijayalakshmi, Birstler Jen, Harrison Adrienne, Scollie Susan, Purcell David
Department of Communication Sciences and Disorders & Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin, USA.
National Centre for Audiology, Western University, London, Ontario, Canada.
Ear Hear. 2020 Nov/Dec;41(6):1732-1746. doi: 10.1097/AUD.0000000000000892.
The present study aimed to (1) evaluate the accuracy of envelope following responses (EFRs) in predicting speech audibility as a function of the statistical indicator used for objective response detection, stimulus phoneme, frequency, and level, and (2) quantify the minimum sensation level (SL; stimulus level above behavioral threshold) needed for detecting EFRs.
In 21 participants with normal hearing, EFRs were elicited by 8 band-limited phonemes in the male-spoken token /susa∫i/ (2.05 sec) presented between 20 and 65 dB SPL in 15 dB increments. Vowels in /susa∫i/ were modified to elicit two EFRs simultaneously by selectively lowering the fundamental frequency (f0) in the first formant (F1) region. The modified vowels elicited one EFR from the low-frequency F1 and another from the mid-frequency second and higher formants (F2+). Fricatives were amplitude-modulated at the average f0. EFRs were extracted from single-channel EEG recorded between the vertex (Cz) and the nape of the neck when /susa∫i/ was presented monaurally for 450 sweeps. The performance of the three statistical indicators, F-test, Hotelling's T, and phase coherence, was compared against behaviorally determined audibility (estimated SL, SL ≥0 dB = audible) using area under the receiver operating characteristics (AUROC) curve, sensitivity (the proportion of audible speech with a detectable EFR [true positive rate]), and specificity (the proportion of inaudible speech with an undetectable EFR [true negative rate]). The influence of stimulus phoneme, frequency, and level on the accuracy of EFRs in predicting speech audibility was assessed by comparing sensitivity, specificity, positive predictive value (PPV; the proportion of detected EFRs elicited by audible stimuli) and negative predictive value (NPV; the proportion of undetected EFRs elicited by inaudible stimuli). The minimum SL needed for detection was evaluated using a linear mixed-effects model with the predictor variables stimulus and EFR detection p value.
of the 3 statistical indicators were similar; however, at the type I error rate of 5%, the sensitivities of Hotelling's T (68.4%) and phase coherence (68.8%) were significantly higher than the F-test (59.5%). In contrast, the specificity of the F-test (97.3%) was significantly higher than the Hotelling's T (88.4%). When analyzed using Hotelling's T as a function of stimulus, fricatives offered higher sensitivity (88.6 to 90.6%) and NPV (57.9 to 76.0%) compared with most vowel stimuli (51.9 to 71.4% and 11.6 to 51.3%, respectively). When analyzed as a function of frequency band (F1, F2+, and fricatives aggregated as low-, mid- and high-frequencies, respectively), high-frequency stimuli offered the highest sensitivity (96.9%) and NPV (88.9%). When analyzed as a function of test level, sensitivity improved with increases in stimulus level (99.4% at 65 dB SPL). The minimum SL for EFR detection ranged between 13.4 and 21.7 dB for F1 stimuli, 7.8 to 12.2 dB for F2+ stimuli, and 2.3 to 3.9 dB for fricative stimuli.
EFR-based inference of speech audibility requires consideration of the statistical indicator used, phoneme, stimulus frequency, and stimulus level.
本研究旨在（1）评估包络跟随反应（EFRs）在预测言语可听度方面的准确性，该准确性是用于客观反应检测的统计指标、刺激音素、频率和强度的函数；（2）量化检测EFRs所需的最小感觉级（SL；高于行为阈值的刺激强度）。
在21名听力正常的受试者中，通过男性发音的/susa∫i/（2.05秒）中的8个带限音素诱发EFRs，该刺激在20至65 dB SPL之间以15 dB的增量呈现。通过在第一共振峰（F1）区域选择性降低基频（f0），对/susa∫i/中的元音进行修改，以同时诱发两个EFRs。修改后的元音从低频F1诱发一个EFR，从中频的第二及更高共振峰（F2+）诱发另一个EFR。摩擦音以平均f0进行幅度调制。当单耳呈现/susa∫i/ 450次扫描时，从记录于头顶（Cz）和颈背之间的单通道脑电图中提取EFRs。使用接受者操作特征（AUROC）曲线下面积、灵敏度（具有可检测EFR的可听言语比例[真阳性率]）和特异性（无可检测EFR的不可听言语比例[真阴性率]），将三种统计指标（F检验、霍特林T检验和相位相干性）的性能与行为确定的可听度（估计的SL，SL≥0 dB = 可听）进行比较。通过比较灵敏度、特异性、阳性预测值（PPV；可听刺激诱发的可检测EFR比例）和阴性预测值（NPV；不可听刺激诱发的未检测到的EFR比例），评估刺激音素、频率和强度对EFRs预测言语可听度准确性的影响。使用包含预测变量刺激和EFR检测p值的线性混合效应模型评估检测所需的最小SL。
三种统计指标的结果相似；然而，在5%的I型错误率下，霍特林T检验（68.4%）和相位相干性（68.8%）的灵敏度显著高于F检验（59.5%）。相比之下，F检验的特异性（97.3%）显著高于霍特林T检验（88.4%）。当使用霍特林T检验作为刺激的函数进行分析时，与大多数元音刺激（分别为51.9%至71.4%和11.6%至51.3%）相比，摩擦音具有更高的灵敏度（88.6%至90.6%）和NPV（57.9%至76.0%）。当作为频带（F1、F2+和摩擦音分别汇总为低频、中频和高频）的函数进行分析时，高频刺激具有最高的灵敏度（96.9%）和NPV（88.9%）。当作为测试强度的函数进行分析时，灵敏度随刺激强度的增加而提高（65 dB SPL时为99.4%）。F1刺激的EFR检测最小SL在13.4至21.7 dB之间，F2+刺激的最小SL在7.8至12.2 dB之间，摩擦音刺激的最小SL在2.3至3.9 dB之间。
基于EFRs推断言语可听度需要考虑所使用的统计指标、音素、刺激频率和刺激强度。
