Intelligibility of normal speakers: Vowel space characteristics

Even within careful speaking conditions, normal speakers vary in intelligibility. This study investigated vowel space characteristics as one correlate of variation in intelligibility. Data consisted of 100 Harvard sentences, spoken by 20 speakers and transcribed by ten listeners per speaker. Formant measurements (mel transformed) of six tokens each for three vowels [i,a,o] provided a basis for assessing the vowel‐space characteristics. First, vowel‐space area was calculated as the Euclidean area between vowel category means. Across all 20 speakers, this area did not correlate with intelligibility. However, for a subset of the speakers (three highest, three lowest in intelligibility) there was a moderate positive correlation (r=+0.34). Second, vowel‐space dispersion was calculated as the mean distance from the center of the triangular space to all 18 tokens. This dispersion measure showed a moderate, positive correlation with intelligibility across all 20 speakers (r=+0.43), suggesting the importance of individual token location for overall intelligibility. Finally, minimum and maximum formant values gave a measure of F1 and F2 range covered by vowel tokens. This measure revealed that F1 range correlated positively with intelligibility (r=+0.53), whereas F2 range did not. The results will be discussed in the context of talker variability and intelligibility.