Tempo, stress, and vowel reduction in American English

Abstract

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.

The strong/weak syllable distinction in English

“…The values obtained for the stressed and reduced vowels were in agreement with those reported elsewhere for such tokens, in British English (Howell and W'tlliams, 1992), American English (Fourakis, 1991), and Dutch (van Son and Pols, 1990).…”

Investigating the nature of aspirated stops in Western Andalusian Spanish

“…A substantial body of research has shown that segments produced at faster rates and unstressed syllables are more sensitive to coarticulatory effects than segments spoken at slow speech rates and in stressed syllables (Lindblom 1963, Gay 1981, Browman & Goldstein 1990, Fourakis 1991, Moon & Lindblom 1994, Byrd & Tan 1996, Davidson 2006, among many others). If postaspiration in Andalusian [h + voiceless stop] clusters is caused by changes in intergestural timing, its duration can be expected to be longer at faster speech rates and in unstressed stop consonants.…”

Duration and spectral balance of intervocalic consonants: A case for efficient communication

“…Quite a large body of research has shown that syllable stress and pitch accent strongly affect vowel duration and the level of vowel reduction (eg., Fourakis, 1991;Koopmans-Van Beinum, 1980;Lindblom, 1990;Van Bergem, 1995;Pols, 1990, 1992;Wang, 1997) and consonant reduction (de Jong et al, 1993;de Jong, 1995;Farnetani, 1995;Pols, 1996, 1999a). An archetypal example of reduction is that of vowel realizations becoming more like a schwa in unstressed syllables (eg., Koopmans-Van Beinum, 1980;Lindblom, 1990;Van Bergem, 1995).…”