Graduate Center of the City University of New York, 365 Fifth Avenue, New York, New York 10016, USA.
J Acoust Soc Am. 2011 Apr;129(4):2068-79. doi: 10.1121/1.3543945.
Medial olivocochlear (MOC) efferent fibers synapse directly on the outer hair cells (OHCs). Efferent activation evoked by contralateral acoustic stimulation (CAS) will affect OHC amplification and subsequent measures of distortion-product otoacoustic emissions (DPOAEs). The aim of this study was to investigate measures of total and separated DPOAEs during efferent activation. Efferent activation produces both suppression and enhancement of the total DPOAE level. Level enhancements occurred near fine-structure minima and were associated with consistent MOC evoked upward shifts in DPOAE fine-structure frequency. Examination of the phase of the separated components revealed that frequency shifts stemmed from increasing phase leads of the reflection component during CAS, while the generator component phase was nearly invariant. Separation of the two DPOAE components responsible for the fine-structure revealed more consistent reduction of the levels of both components. Using vector subtraction (which takes into account both level and phase) to estimate the changes in the unseparated DPOAE provided consistent evidence of DPOAE suppression. Including phase information provided a more sensitive, valid and consistent estimate of CAS function even if one does not know the position of the DPOAE in the fine-structure.
内侧橄榄耳蜗（MOC）传出纤维直接与外毛细胞（OHC）突触连接。对侧声刺激（CAS）引起的传出激活将影响 OHC 放大和随后的畸变产物耳声发射（DPOAE）测量。本研究旨在研究传出激活期间总 DPOAE 和分离 DPOAE 的测量。传出激活会产生总 DPOAE 水平的抑制和增强。在精细结构最小值附近发生水平增强，并且与 MOC 诱发的 DPOAE 精细结构频率的一致向上移位相关。对分离分量的相位进行检查表明，频率移位源于 CAS 期间反射分量的相位逐渐提前，而发生器分量的相位几乎不变。分离负责精细结构的两个 DPOAE 分量显示两个分量的水平更一致地降低。使用向量相减（考虑到水平和相位）来估计未分离的 DPOAE 的变化，即使不知道 DPOAE 在精细结构中的位置，也能提供 DPOAE 抑制的一致证据。即使不知道 DPOAE 在精细结构中的位置，包含相位信息也能提供更敏感、更有效和更一致的 CAS 功能估计。
