Mäkelä A M, Alku P, May P J C, Mäkinen V, Tiitinen H
Apperception and Cortical Dynamics, Department of Psychology, University of Helsinki, Finland.
Neurol Clin Neurophysiol. 2004 Nov 30;2004:91.
Cortical activity underlying speech perception has been studied mostly by using isolated vowels with constant formant frequencies. Speech, however, is characterized by formant transitions whereby formant frequencies change as a function of time. We used magnetoencephalography (MEG) to investigate cortical activity elicited by isolated vowels and diphthongs containing formant transitions. Ten subjects were presented with two isolated vowels /a/ and /u/ and diphthongs /au/ and /ua/. Stimulus duration was 200 ms, and the diphthongs started and ended with a 50-ms constant-formant period and included a 100-ms linear transition period. Apart from studying the auditory N100m response, we examined subsequent brain activity in a 500-ms poststimulus time window, as the transitions were expected to elicit activity also in later stages of cognitive processing. All the stimuli elicited prominent N100m responses. Thereafter, both the isolated vowels and diphthongs elicited sustained brain activity lasting up to 500 ms. The present observations indicate that identification of the speech sounds as well as changes in their identity are reflected in the auditory N100m. Notably, the stimuli appeared to elicit left-hemispheric activity resembling the N400, typically obtained by using more complicated speech stimuli such as words and sentences.
言语感知背后的皮层活动大多是通过使用具有恒定共振峰频率的孤立元音来进行研究的。然而，言语的特征是共振峰过渡，即共振峰频率随时间变化。我们使用脑磁图（MEG）来研究由包含共振峰过渡的孤立元音和双元音引发的皮层活动。向10名受试者呈现两个孤立元音/a/和/u/以及双元音/au/和/ua/。刺激持续时间为200毫秒，双元音以50毫秒的恒定共振峰期开始和结束，并包括一个100毫秒的线性过渡期。除了研究听觉N100m反应外，我们还在刺激后500毫秒的时间窗口内检查了随后的大脑活动，因为预期这些过渡也会在认知处理的后期阶段引发活动。所有刺激都引发了明显的N100m反应。此后，孤立元音和双元音都引发了持续长达500毫秒的大脑活动。目前的观察结果表明，语音的识别以及其特征的变化都反映在听觉N100m中。值得注意的是，这些刺激似乎引发了类似于N400的左半球活动，通常是通过使用更复杂的语音刺激（如单词和句子）获得的。
