Ecole Normale Supérieure, Inserm U960, Paris, France.
Laryngoscope. 2012 Jan;122(1):167-73. doi: 10.1002/lary.22370. Epub 2011 Nov 17.
Language processing from the cochlea to auditory association cortices shows side-dependent specificities with an apparent left hemispheric dominance. The aim of this article was to propose to nonspeech specialists a didactic review of two complementary theories about hemispheric asymmetry in speech processing. Starting from anatomico-physiological and clinical observations of auditory asymmetry and interhemispheric connections, this review then exposes behavioral (dichotic listening paradigm) as well as functional (functional magnetic resonance imaging and positron emission tomography) experiments that assessed hemispheric specialization for speech processing. Even though speech at an early phonological level is regarded as being processed bilaterally, a left-hemispheric dominance exists for higher-level processing. This asymmetry may arise from a segregation of the speech signal, broken apart within nonprimary auditory areas in two distinct temporal integration windows--a fast one on the left and a slower one on the right--modeled through the asymmetric sampling in time theory or a spectro-temporal trade-off, with a higher temporal resolution in the left hemisphere and a higher spectral resolution in the right hemisphere, modeled through the spectral/temporal resolution trade-off theory. Both theories deal with the concept that lower-order tuning principles for acoustic signal might drive higher-order organization for speech processing. However, the precise nature, mechanisms, and origin of speech processing asymmetry are still being debated. Finally, an example of hemispheric asymmetry alteration, which has direct clinical implications, is given through the case of auditory aging that mixes peripheral disorder and modifications of central processing.
从耳蜗到听觉联合皮质的语言处理显示出与明显的左半球优势相关的侧依赖性特异性。本文的目的是向非语音专家推荐一种关于言语处理半球不对称的两种互补理论的教学综述。从听觉不对称和半球间连接的解剖生理和临床观察出发，本综述随后介绍了评估言语处理半球专业化的行为（双听范式）和功能（功能磁共振成像和正电子发射断层扫描）实验。尽管早期语音水平的语音被认为是双侧处理的，但在更高水平的处理中存在左半球优势。这种不对称可能源于言语信号的分离，在非主要听觉区域内被分成两个不同的时间整合窗口——左侧的快速窗口和右侧的较慢窗口——通过时间理论的不对称采样或频谱-时间权衡来建模，其在左半球具有更高的时间分辨率，在右半球具有更高的频谱分辨率，通过频谱/时间分辨率权衡理论来建模。这两个理论都涉及到这样一个概念，即用于声学信号的较低阶调谐原理可能会驱动言语处理的较高阶组织。然而，言语处理不对称的精确性质、机制和起源仍在争论中。最后，通过听觉老化的案例给出了一个半球不对称改变的例子，该案例混合了外围障碍和中枢处理的改变，具有直接的临床意义。
