National Research Council (CNR), Institute of Biomedical Engineering, I-20133 Milan, Italy.
IEEE Trans Biomed Circuits Syst. 2013 Aug;7(4):401-13. doi: 10.1109/TBCAS.2012.2223212.
A new approach to study nonlinearity in cochlear active mechanisms, as evaluated in transient evoked otoacoustic emissions (TEOAEs), is presented. TEOAEs are signals generated in the cochlea by a mix of linear and nonlinear mechanisms. This new approach was designed to complement the traditional TEOAE analysis performed by currently available systems used in objective hearing screening and assessment. Nonlinearity of TEOAEs was studied by means of the bispectrum, which is able to find out quadratic frequency couplings (QFCs) that occur when a frequency is not only generated by an independent cochlear source, but it is the result of the interaction among a number of cochlear sources. To fit with the technical constraints of currently available TEOAE systems, the bispectrum was estimated by the third-order scaled polyperiodogram. The proposed method was characterized with synthesized TEOAEs as a function of the main TEOAE parameters and then used to analyze TEOAEs recorded in normal hearing adults and full-term neonates. Results revealed the presence of QFCs in both adult and neonatal TEOAEs, with peculiar patterns and significantly different frequency content in the two groups: adults had QFCs mainly around 2 kHz and neonates had QFCs mainly in the range 3.5-4 kHz.
本文提出了一种研究耳蜗主动机制中非线性的新方法，该方法通过瞬态诱发耳声发射（TEOAEs）进行评估。TEOAEs 是由混合的线性和非线性机制在耳蜗中产生的信号。这种新方法旨在补充目前用于客观听力筛查和评估的可用系统中进行的传统 TEOAE 分析。通过双谱来研究 TEOAEs 的非线性，双谱能够找到当一个频率不仅由独立的耳蜗源产生，而且是多个耳蜗源相互作用的结果时出现的二次频率耦合（QFC）。为了适应目前可用的 TEOAE 系统的技术限制，通过三阶缩放多周期图来估计双谱。该方法的特点是作为主要 TEOAE 参数的函数来合成 TEOAEs，然后用于分析正常听力成年人和足月新生儿的 TEOAEs。结果表明，成年人和新生儿的 TEOAEs 中都存在 QFC，在两组中具有特殊的模式和明显不同的频率内容：成年人的 QFC 主要集中在 2 kHz 左右，而新生儿的 QFC 主要集中在 3.5-4 kHz 范围内。
