Vihla M, Lounasmaa O V, Salmelin R
Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, Post Office Box 2200, 02015 HUT, Espoo, Finland.
Proc Natl Acad Sci U S A. 2000 Sep 12;97(19):10590-4. doi: 10.1073/pnas.180317297.
We compared magnetoencephalographic responses for natural vowels and for sounds consisting of two pure tones that represent the two lowest formant frequencies of these vowels. Our aim was to determine whether spectral changes in successive stimuli are detected differently for speech and nonspeech sounds. The stimuli were presented in four blocks applying an oddball paradigm (20% deviants, 80% standards): (i) /alpha/ tokens as deviants vs. /i/ tokens as standards; (ii) /e/ vs. /i/; (iii) complex tones representing /alpha/ formants vs. /i/ formants; and (iv) complex tones representing /e/ formants vs. /i/ formants. Mismatch fields (MMFs) were calculated by subtracting the source waveform produced by standards from that produced by deviants. As expected, MMF amplitudes for the complex tones reflected acoustic deviation: the amplitudes were stronger for the complex tones representing /alpha/ than /e/ formants, i.e., when the spectral difference between standards and deviants was larger. In contrast, MMF amplitudes for the vowels were similar despite their different spectral composition, whereas the MMF onset time was longer for /e/ than for /alpha/. Thus the degree of spectral difference between standards and deviants was reflected by the MMF amplitude for the nonspeech sounds and by the MMF latency for the vowels.
我们比较了自然元音以及由两个纯音组成的声音（这两个纯音代表了这些元音的两个最低共振峰频率）的脑磁图反应。我们的目的是确定对于语音和非语音声音，连续刺激中的频谱变化是否会被不同地检测到。刺激以四个组块呈现，采用奇偶数范式（20%偏差刺激音，80%标准刺激音）：（i）/α/音素作为偏差刺激音与/i/音素作为标准刺激音；（ii）/e/与/i/；（iii）代表/α/共振峰的复合音与代表/i/共振峰的复合音；以及（iv）代表/e/共振峰的复合音与代表/i/共振峰的复合音。失配场（MMF）通过从偏差刺激音产生的源波形中减去标准刺激音产生的源波形来计算。正如预期的那样，复合音的MMF振幅反映了声学偏差：代表/α/的复合音的振幅比代表/e/共振峰的复合音更强，即当标准刺激音和偏差刺激音之间的频谱差异更大时。相比之下，尽管元音的频谱组成不同，但其MMF振幅相似，而/e/的MMF起始时间比/α/的更长。因此，标准刺激音和偏差刺激音之间的频谱差异程度在非语音声音中由MMF振幅反映，在元音中由MMF潜伏期反映。
