The correlation of vowel space and speech intelligibility for individuals with cerebral palsy

Abstract

The relationship between the area of the vowel space (F1/F2 space) and speech intelligibility was studied in a group of 20 Mandarin-Chinese-speaking young adults with cerebral palsy. Subjects read aloud 18 bisyllabic words containing the vowels /i/, /a/, and /u/ using their habitual speaking rate. The words were identified by three normal listeners and the percent corrects of vowel identifications were used as speech intelligibility for the individual cerebral-palsied speakers. Results revealed that cerebral-palsied speakers’ intelligibility varied greatly across individuals (scores ranged from 36% to 100%). Speakers with cerebral palsy exhibited smaller vowel space areas when compared to 10 age-matched controls. The correlation between vowel space area and speech intelligibility was significant (r=0.612, p<0.005). Cerebral-palsied speakers with larger vowels spaces were generally more intelligible than speakers with reduced vowel spaces. These results suggest that vowel space area can serve as an important component of overall estimates of speech intelligibility, and will be related to data collected in studies comparing infant-directed (ID) versus adult-directed (AD) speech, which show that speakers use significantly larger vowel areas when engaged in ID speech. [Work funded by NIH, HFSP, and the Talaris Research Institute.]