McClaskey Carolyn M, Dias James W, Dubno Judy R, Harris Kelly C
Medical University of South Carolina, Charleston.
J Speech Lang Hear Res. 2018 Sep 19;61(9):2422-2430. doi: 10.1044/2018_JSLHR-H-18-0097.
Human auditory nerve (AN) activity estimated from the amplitude of the first prominent negative peak (N1) of the compound action potential (CAP) is typically quantified using either a peak-to-peak measurement or a baseline-corrected measurement. However, the reliability of these 2 common measurement techniques has not been evaluated but is often assumed to be relatively poor, especially for older adults. To address this question, the current study (a) compared test-retest reliability of these 2 methods and (b) tested the extent to which measurement type affected the relationship between N1 amplitude and experimental factors related to the stimulus (higher and lower intensity levels) and participants (younger and older adults).
Click-evoked CAPs were recorded in 24 younger (aged 18-30 years) and 20 older (aged 55-85 years) adults with clinically normal audiograms up to 3000 Hz. N1 peak amplitudes were estimated from peak-to-peak measurements (from N1 to P1) and baseline-corrected measurements for 2 stimulus levels (80 and 110 dB pSPL). Baseline-corrected measurements were made with 4 baseline windows. Each stimulus level was presented twice, and test-retest reliability of these 2 measures was assessed using the intraclass correlation coefficient. Linear mixed models were used to evaluate the extent to which age group and click level uniquely predicted N1 amplitude and whether the predictive relationships differed between N1 measurement techniques.
Both peak-to-peak and baseline-corrected measurements of N1 amplitude were found to have good-to-excellent reliability, with intraclass correlation coefficient values > 0.60. As expected, N1 amplitudes were significantly larger for younger participants compared with older participants for both measurement types and were significantly larger in response to clicks presented at 110 dB pSPL than at 80 dB pSPL for both measurement types. Furthermore, the choice of baseline window had no significant effect on N1 amplitudes using the baseline-corrected method.
Our results suggest that measurements of AN activity can be robustly and reliably recorded in both younger and older adults using either peak-to-peak or baseline-corrected measurements of the N1 of the CAP. Peak-to-peak measurements yield larger N1 response amplitudes and are the default measurement type for many clinical systems, whereas baseline-corrected measurements are computationally simpler. Furthermore, the relationships between AN activity and stimulus- and participant-related variables were not affected by measurement technique, which suggests that these relationships can be compared across studies using different techniques for measuring the CAP N1.
从复合动作电位（CAP）的第一个显著负峰（N1）的幅度估计的人类听神经（AN）活动，通常使用峰峰值测量或基线校正测量进行量化。然而，这两种常用测量技术的可靠性尚未得到评估，但通常被认为相对较差，尤其是对于老年人。为了解决这个问题，本研究（a）比较了这两种方法的重测可靠性，（b）测试了测量类型对N1幅度与与刺激（更高和更低强度水平）和参与者（年轻人和老年人）相关的实验因素之间关系的影响程度。
对24名年龄在18至30岁之间的年轻人和20名年龄在55至85岁之间的老年人进行了点击诱发的CAP记录，这些人的听力图在3000Hz以下临床正常。从峰峰值测量（从N1到P1）和针对两种刺激水平（80和110dB pSPL）的基线校正测量中估计N1峰值幅度。基线校正测量使用4个基线窗口进行。每个刺激水平呈现两次，使用组内相关系数评估这两种测量的重测可靠性。使用线性混合模型评估年龄组和点击水平对N1幅度的独特预测程度，以及N1测量技术之间的预测关系是否不同。
发现N1幅度的峰峰值测量和基线校正测量都具有良好到优秀的可靠性，组内相关系数值>0.60。正如预期的那样，对于两种测量类型，年轻参与者的N1幅度显著大于老年参与者，并且对于两种测量类型，在110dB pSPL呈现的点击响应中N1幅度显著大于在80dB pSPL呈现的点击响应。此外，使用基线校正方法时，基线窗口的选择对N1幅度没有显著影响。
我们的结果表明，使用CAP的N1的峰峰值测量或基线校正测量，可以在年轻人和老年人中稳健且可靠地记录AN活动。峰峰值测量产生更大的N1响应幅度，是许多临床系统的默认测量类型，而基线校正测量在计算上更简单。此外，AN活动与刺激和参与者相关变量之间的关系不受测量技术的影响，这表明可以在使用不同技术测量CAP N1的研究之间比较这些关系。
