Altmann Christian F, Uesaki Maiko, Ono Kentaro, Matsuhashi Masao, Mima Tatsuya, Fukuyama Hidenao
Human Brain Research Center, Graduate School of Medicine, Kyoto University, 54 Shogoin Kawaracho, Sakyo-ku, Kyoto 606-8507, Japan; Career-Path Promotion Unit for Young Life Scientists, Kyoto University, Kyoto 606-8501, Japan.
Career-Path Promotion Unit for Young Life Scientists, Kyoto University, Kyoto 606-8501, Japan; Department of Psychology, Graduate School of Letters, Kyoto University, Kyoto 606-8501, Japan.
Neuropsychologia. 2014 Nov;64:13-23. doi: 10.1016/j.neuropsychologia.2014.09.006. Epub 2014 Sep 16.
Categorical perception of phonemes describes the phenomenon that, when phonemes are classified they are often perceived to fall into distinct categories even though physically they follow a continuum along a feature dimension. While consonants such as plosives have been proposed to be perceived categorically, the representation of vowels has been described to be more continuous. We aimed at testing this difference in representation at a behavioral and neurophysiological level using human magnetoencephalography (MEG). To this end, we designed stimuli based on natural speech by morphing along a phonological continuum entailing changes of the voiced stop-consonant or the steady-state vowel of a consonant-vowel (CV) syllable. Then, while recording MEG, we presented participants with consecutive pairs of either same or different CV syllables. The differences were such that either both CV syllables were from within the same category or belonged to different categories. During the MEG experiment, the participants actively discriminated the stimulus pairs. Behaviorally, we found that discrimination was easier for the between-compared to the within-category contrast for both consonants and vowels. However, this categorical effect was significantly stronger for the consonants compared to vowels, in line with a more continuous representation of vowels. At the neural level, we observed significant repetition suppression of MEG evoked fields, i.e. lower amplitudes for physically same compared to different stimulus pairs, at around 430 to 500ms after the onset of the second stimulus. Source reconstruction revealed generating sources of this repetition suppression effect within left superior temporal sulcus and gyrus, posterior to Heschl׳s gyrus. A region-of-interest analysis within this region showed a clear categorical effect for consonants, but not for vowels, providing further evidence for the important role of left superior temporal areas in categorical representation during active phoneme discrimination.
当对音素进行分类时，尽管从物理特征维度来看它们遵循连续变化，但人们通常会将它们感知为属于不同的类别。虽然有人提出爆破音等辅音是被范畴性地感知的，但元音的表征被描述为更具连续性。我们旨在使用人类脑磁图（MEG）在行为和神经生理水平上测试这种表征差异。为此，我们通过沿着一个语音连续体进行变形来设计基于自然语音的刺激，该连续体涉及辅音 - 元音（CV）音节中浊塞音或稳态元音的变化。然后，在记录脑磁图时，我们向参与者呈现连续的相同或不同CV音节对。这些差异在于，要么两个CV音节都来自同一类别，要么属于不同类别。在脑磁图实验中，参与者积极区分刺激对。在行为层面，我们发现对于辅音和元音，类别间对比的辨别比类别内对比更容易。然而，与元音相比，辅音的这种范畴效应明显更强，这与元音更具连续性的表征一致。在神经层面，我们观察到在第二个刺激开始后约430至500毫秒时，脑磁图诱发场出现显著的重复抑制，即与不同刺激对相比，物理上相同的刺激对的振幅更低。源重建显示这种重复抑制效应的产生源在左侧颞上沟和颞上回，位于颞横回后方。该区域内的感兴趣区域分析显示辅音有明显的范畴效应，而元音没有，这进一步证明了左侧颞上区域在主动音素辨别过程中的范畴表征中起着重要作用。
