THE INFLUENCE OF SPEAKING RATE ON VOWEL SPACE AND SPEECH-INTELLIGIBILITY FOR INDIVIDUALS WITH AMYOTROPHIC-LATERAL-SCLEROSIS

The relationship between speaking rate, vowel space area, and speech i ntelligibility was studied in a-group of 9 subjects with amyotrophic l ateral sclerosis (ALS) and 9 age- and gender-matched controls. Subject s 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 w ords containing the vowels /i/, /ae/, /a/, and /u/. To quantify change s in vowel space area across speaking rate, the area of the vowel quad rilateral was calculated for each speaker at each speaking rate. In ad dition, intelligibility estimates at each speaking rate were obtained for the dysarthric, speakers. Results revealed that dysarthric speaker s exhibited smaller vowel space areas and less systematic changes in v owel space as a function of speaking rate, when compared to the neurol ogically intact speakers. In an examination of the relationship betwee n vowel space area and speech intelligibility; vowel Space was found t o account for 45% of the variance in speech intelligibility. This resu lt suggests that vowel space area is an important component global est imates of speech intelligibility.