Sommers M S, Kewley-Port D
Department of Psychology, Washington University in St. Louis, Missouri 63130, USA.
J Acoust Soc Am. 1996 Jun;99(6):3770-81. doi: 10.1121/1.414972.
The present investigations were designed to establish the features of vowel spectra that mediate formant frequency discrimination. Thresholds for detecting frequency shifts in the first and second formants of two steady-state vowels were initially measured for conditions in which the amplitudes of all harmonics varied in accordance with a model of cascade formant synthesis. In this model, changes in formant frequency produce level variations in components adjacent to the altered formant as well as in harmonics spectrally remote from the shifted resonant frequency. Discrimination thresholds determined with the cascade synthesis procedure were then compared to difference limens (DLs) obtained when the number of harmonics exhibiting level changes was limited to the frequency region surrounding the altered formant. Results indicated that amplitude variations could be restricted to one to three components near the shifted formant before significant increases in formant frequency DLs were observed. In a second experiment, harmonics remote from the shifted formant were removed from the stimuli. In most cases, thresholds for these reduced-harmonic complexes were not significantly different from those obtained with full-spectrum vowels. Preliminary evaluation of an excitation-pattern model of formant frequency discrimination indicated that such a model can provide good accounts of the thresholds obtained in the present experiments once the salient regions of the vowel spectra have been identified. Implications of these findings for understanding the mechanism mediating vowel perception are discussed.
本研究旨在确定介导共振峰频率辨别力的元音频谱特征。最初，在所有谐波的幅度根据级联共振峰合成模型变化的条件下，测量了两个稳态元音的第一和第二共振峰频率偏移的检测阈值。在该模型中，共振峰频率的变化会使与改变的共振峰相邻的分量以及与移动的共振频率在频谱上相距较远的谐波的电平发生变化。然后将通过级联合成程序确定的辨别阈值与当表现出电平变化的谐波数量限制在改变的共振峰周围的频率区域时获得的差别阈（DLs）进行比较。结果表明，在观察到共振峰频率差别阈显著增加之前，幅度变化可以限制在移动的共振峰附近的一到三个分量。在第二个实验中，将与移动的共振峰相距较远的谐波从刺激中去除。在大多数情况下，这些谐波减少的复合体的阈值与全频谱元音获得的阈值没有显著差异。对共振峰频率辨别力的激发模式模型的初步评估表明，一旦确定了元音频谱的显著区域，这样的模型可以很好地解释本实验中获得的阈值。讨论了这些发现对理解介导元音感知的机制的意义。
