An Acoustic Study of Vowels Produced by Alaryngeal Speakers in Taiwan

This study investigated the acoustic properties of 6 Taiwan Southern Min vowels produced by 10 laryngeal speakers (LA), 10 speakers with a pneumatic artificial larynx (PA), and 8 esophageal speakers (ES).

Each of the 6 monophthongs of Taiwan Southern Min (/i, e, a, ɔ, u, ə/) was represented by a Taiwan Southern Min character and appeared randomly on a list 3 times (6 Taiwan Southern Min characters × 3 repetitions = 18 tokens). Each Taiwan Southern Min character in this study has the same syllable structure, /V/, and all were read with tone 1 (high and level). Acoustic measurements of the 1st formant, 2nd formant, and 3rd formant were taken for each vowel. Then, vowel space areas (VSAs) enclosed by /i, a, u/ were calculated for each group of speakers. The Euclidean distance between vowels in the pairs /i, a/, /i, u/, and /a, u/ was also calculated and compared across the groups.

PA and ES have higher 1st or 2nd formant values than LA for each vowel. The distance is significantly shorter between vowels in the corner vowel pairs /i, a/ and /i, u/. PA and ES have a significantly smaller VSA compared with LA.

In accordance with previous studies, alaryngeal speakers have higher formant frequency values than LA because they have a shortened vocal tract as a result of their total laryngectomy. Furthermore, the resonance frequencies are inversely related to the length of the vocal tract (on the basis of the assumption of the source filter theory). PA and ES have a smaller VSA and shorter distances between corner vowels compared with LA, which may be related to speech intelligibility. This hypothesis needs further support from future study.