Fourakis M
Central Institute for the Deaf, St. Louis, Missouri 63110.
J Acoust Soc Am. 1991 Oct;90(4 Pt 1):1816-27. doi: 10.1121/1.401662.
Two processes that affect the acoustic characteristics of vowels, namely, phonological and phonetic vowel reduction are discussed. Phonological vowel reduction applies to unstressed vowels. Phonetic vowel reduction is supposed to apply to all vowels and be caused by fast speech rates, context, as well as lack of stress. In this experiment, the effects of changes in stress and in rate of speech (tempo) on the acoustic characteristics of American English monophthongal, nonretroflex vowels were examined. Four male and four female native speakers produced these vowels in two contexts, [h_d] and [b_d], in a carrier sentence, under four conditions of tempo stress (slow-stressed, slow-unstressed, fast-stressed, and fast-unstressed). Measurements of duration and fundamental frequency showed that the subjects did, in fact, vary tempo and stress as instructed. The effect of a change in stress on vowel duration was found to be slightly larger than that of a change in tempo. The putative vowel portion of each utterance was analyzed, formant tracks were obtained, and these were plotted in an auditory-perceptual space [J.D. Miller, J. Acoust. Soc. AM. 85, 2114-2134 (1989)]. These plots served to determine the part of the utterance that could, in most cases, be considered its steady state. For each utterance, an average of the coordinates of this steady-state portion was taken and was used to represent the utterance as a point in the auditory-perceptual space. The distance of these data points from the point representing the acoustic characteristics of a vowel produced by a neutral vocal tract was used to determine the magnitude of phonetic vowel reduction caused by faster tempo and less stress, relative to the slow-stressed condition. Although the results indicate that tempo and stress may not have a major influence on the distances of individual vowels from the neutral point, the size of the vowel space overall was affected. The vowel space was largest for the slow stressed condition and smallest for the fast unstressed condition. In addition, several vowel classifications schemes were tested using linear discriminant analysis, and the one proposed by Miller (1989) performed better than other combinations of fundamental frequency and the first three formants.
本文讨论了影响元音声学特征的两个过程，即音系学上的元音弱化和语音学上的元音弱化。音系学上的元音弱化适用于非重读音节中的元音。语音学上的元音弱化被认为适用于所有元音，其成因包括语速过快、语境以及缺乏重音。在本实验中，研究了重音和语速（节奏）变化对美式英语单元音、非卷舌元音声学特征的影响。四名男性和四名女性以母语者身份在两种语境（[h_d]和[b_d]）下，于一个载体句子中，在四种节奏重音条件（慢速重读、慢速非重读、快速重读和快速非重读）下发出这些元音。时长和基频的测量结果表明，受试者确实按照指示改变了节奏和重音。结果发现，重音变化对元音时长的影响略大于节奏变化。对每个发音的假定元音部分进行了分析，获取了共振峰轨迹，并将其绘制在听觉感知空间中[J.D. 米勒，《美国声学学会杂志》85, 2114 - 2134 (1989)]。这些图表用于确定在大多数情况下可被视为发音稳态部分的发音段落。对于每个发音，取该稳态部分坐标的平均值，并将其作为一个点用于在听觉感知空间中表示该发音。这些数据点与代表中性声道发出元音声学特征的点之间的距离，用于确定相对于慢速重读条件，由较快节奏和较小重音导致的语音学上元音弱化的程度。尽管结果表明节奏和重音可能对单个元音与中性点的距离没有重大影响，但元音空间的整体大小受到了影响。慢速重读条件下的元音空间最大，快速非重读条件下的元音空间最小。此外，使用线性判别分析测试了几种元音分类方案，米勒（1989）提出的方案比其他基频与前三个共振峰组合的方案表现更好。
