Speech intelligibility and the vowel space: Normal speech

Abstract

Vowel formant frequency values and related vowel space measures have been widely used in the study of speech intelligibility for normal and disordered talkers. The strength of vowel space measures in predicting speech intelligibility for normal talkers, however, is relatively low: [Bradlow et al. (1996)] found that vowel space dispersion predicted 19% of variance in sentence intelligibility, and [Hazan and Markham (2004)] found that the F2 difference between /i/ and /u/ predicted 16% of variance in word intelligibility scores. Using data from the 45 men and 48 women speakers in the Hillenbrand et al. (1995) database, acoustic characteristics of ten vowels were used to predict identification accuracy. Multiple regressions revealed that global measures (mean f0, F1 and F2, duration, and amount of formant movement) and fine-grained measures (vowel space area, mean distance among vowels, ranges for f0, F1, and F2, duration ratio between long and short vowels, and dynamic ratio between dynamic and static vowels) accounted for less than one-quarter of the variance in identification scores across talkers. Focusing on confusions among spectrally similar vowels may provide better information on intelligibility differences among normal talkers. Goodness ratings may provide a wider range of scores for statistical analysis than identification accuracy.