The Influence of Speaking Rate on Vowel Space and Speech Intelligibility for Individuals With Amyotrophic Lateral Sclerosis

TLDR

The study measured vowel durations and formant frequencies for selected vowels in 9 ALS patients and 9 matched controls while they read a standard passage at habitual, fast, and slow rates, then calculated vowel quadrilateral areas and obtained intelligibility estimates for the dysarthric speakers. Dysarthric ALS speakers showed reduced vowel space areas and less systematic rate‑related changes than controls, and vowel space explained 45 % of the variance in speech intelligibility, underscoring its importance for global intelligibility estimates.

Abstract

The relationship between speaking rate, vowel space area, and speech intelligibility was studied in a group of 9 subjects with amyotrophic lateral sclerosis (ALS) and 9 age- and gender-matched controls. Subjects read a standard passage (the Farm Passage) at three speaking rates, including HABITUAL, FAST, and SLOW. Vowel segment durations and target formant frequencies were measured at each speaking rate from select words containing the vowels /i/, /æ/, /a/, and /u/. To quantify changes in vowel space area across speaking rate, the area of the vowel quadrilateral was calculated for each speaker at each speaking rate. In addition, intelligibility estimates at each speaking rate were obtained for the dysarthric speakers. Results revealed that dysarthric speakers exhibited smaller vowel space areas and less systematic changes in vowel space as a function of speaking rate, when compared to the neurologically intact speakers. In an examination of the relationship between vowel space area and speech intelligibility, vowel space was found to account for 45% of the variance in speech intelligibility. This result suggests that vowel space area is an important component of global estimates of speech intelligibility.