基于样本熵的听觉神经锁相机理的实验分析

锁相是指系统的响应与周期性刺激的特定相位同步的物理现象. 听觉神经的锁相对揭示人的听觉认知基本的神经机理及改善听觉感知有重要意义. 然而, 现有研究主要集中于心理物理方法和幅度谱分析, 不能有效区分包络响应和时域细节结构响应, 不能直观反映神经锁相. 本文主要利用拔靴法和离散傅里叶变换, 提出了基于样本熵的时域细节结构频率跟随响应(temporal-fine-structure-related frequency following response, FFR_T)的神经锁相值(phase locking value, PLV)计算方法, 用于分析神经物理实验数据. 两个脑电实验结果表明: FFR_T的PLV样本熵显著大于包络相关频率跟随响应(envelope-related frequency following response, FFR_E)的PLV, 且二者正交独立, 新方法能有效地分别反映听觉系统对包络和时间细节结构的锁相机理; 基频处的响应主要来源于FFR_E的锁相; 基频处, 不可分辨谐波成分包络的锁相能力优于对可分辨谐波; 基频缺失时, 畸变产物是不同的听觉神经通路的FFR_E的混合; 谐波处, FFR_E 集中于低频, FFR_T则集中于中、高频; 听觉神经元锁相能力与声源的频率可分辨性相关. FFR_T的PLV方法克服了现有FFR分析的局限性, 可用于深入研究听觉神经机理.

Experimental analysis of auditory mechanism of neural phase-locking based on sample entropy

Phase-locking is a physical phenomenon that refers to a system response which is synchronized with a specific phase of the periodic stimulus. The auditory neural phase-locking plays an important role in revealing the basic neural mechanism of auditory cognition and improving auditory perception. In the existing auditory researches, psychophysical and amplitude spectral methods are mainly adopted. However, those two methods cannot differentiate the envelope-related auditory response from the temporal-fine-structure-related auditory response, and cannot reveal the neural phase-locking mechanism directly either. In this study, a phase locking value (PLV), based on sample entropy, bootstrapping and discrete Fourier transform, is proposed for analyzing the temporal-fine-structure-related frequency following response (FFR_T). The proposed PLV is applied to computing neural and physical data. Two electroencephalography experiments are carried out. Results show that the sample entropy of FFR_T's PLV is significantly greater than that of FFR_E's PLV, and the two PLVs are orthogonal and independent. Thus, the PLVs of FFR_E and FFR_T reveal the auditory phase-locking mechanisms effectively. In addition, the response to fundamental frequency is mainly attributed to the envelope-related phase locking. And human auditory capability of phase locking to the envelope of the unresolved frequency is superior to the capability of phase-locking to the envelope of the resolved frequency. Moreover, in the case of missing fundamental frequency, the distortion product is the mixture of FFR_E in various auditory neural paths. Also, FFR_E concentrates at the low harmonic frequencies, while FFR_T concentrates at the mid and high order harmonic frequencies. Therefore, the auditory neural phase-locking is related to the frequency resolution of sound. In conclusion, the proposed method overcomes some disadvantages of existing FFR analyses, making it beneficial to exploring auditory neural mechanisms.