ExpORL, Department of Neurosciences, Katholieke Universiteit Leuven, Leuven, Belgium.
Ear Hear. 2012 Jan-Feb;33(1):134-43. doi: 10.1097/AUD.0b013e31822c26b9.
Speech intelligibility is strongly influenced by the ability to process temporal modulations. It is hypothesized that in dyslexia, deficient processing of rapidly changing auditory information underlies a deficient development of phonological representations, causing reading and spelling problems. Low-frequency modulations between 4 and 20 Hz correspond to the processing rate of important phonological segments (syllables and phonemes, respectively) in speech and therefore provide a bridge between low-level auditory and phonological processing. In the present study, temporal modulation processing was investigated by auditory steady state responses (ASSRs) in normal-reading and dyslexic adults.
Multichannel ASSRs were recorded in normal-reading and dyslexic adults in response to speech-weighted noise stimuli amplitude modulated at 80, 20, and 4 Hz. The 80 Hz modulation is known to be primarily generated by the brainstem, whereas the 20 and 4 Hz modulations are mainly generated in the cortex. Furthermore, the 20 and 4 Hz modulations provide an objective auditory performance measure related to phonemic- and syllabic-rate processing. In addition to neurophysiological measures, psychophysical tests of speech-in-noise perception and phonological awareness were assessed.
On the basis of response strength and phase coherence measures, normal-reading and dyslexic participants showed similar processing at the brainstem level. At the cortical level of the auditory system, dyslexic subjects demonstrated deviant phonemic-rate responses compared with normal readers, whereas no group differences were found for the syllabic rate. Furthermore, a relationship between phonemic-rate ASSRs and psychophysical tests of speech-in-noise perception and phonological awareness was obtained.
The results suggest reduced cortical processing for phonemic-rate modulations in dyslexic adults, presumably resulting in limited integration of temporal information in the dorsal phonological pathway.
言语可懂度受处理时间调制能力的强烈影响。假设在阅读障碍中，快速变化的听觉信息处理能力缺陷导致音位表征发展不足，从而导致阅读和拼写问题。4 至 20 赫兹之间的低频调制对应于语音中重要音位段（音节和音素）的处理速率，因此提供了低水平听觉和音位处理之间的桥梁。在本研究中，通过正常阅读和阅读障碍成人的听觉稳态响应（ASSR）研究了时间调制处理。
正常阅读和阅读障碍成人在响应语音加权噪声刺激时记录多通道 ASSR，该刺激以 80、20 和 4 Hz 的幅度调制。已知 80 Hz 的调制主要由脑干产生，而 20 和 4 Hz 的调制主要由皮层产生。此外，20 和 4 Hz 的调制提供了与音位和音节处理速率相关的客观听觉性能测量。除了神经生理测量外，还评估了语音噪声感知和音位意识的心理物理测试。
基于响应强度和相位相干性测量，正常阅读和阅读障碍参与者在脑干水平表现出相似的处理。在听觉系统的皮层水平上，阅读障碍受试者与正常阅读者相比表现出异常的音位率反应，而在音节率方面则没有发现组间差异。此外，还获得了音位率 ASSR 与语音噪声感知和音位意识的心理物理测试之间的关系。
结果表明，阅读障碍成人的音位率调制皮质处理减少，可能导致背侧音位通路中时间信息的有限整合。
