Acoustic and durational correlates of diphthong contrasts in Nafsan

Abstract

The phonetic realization of diphthongs, vowels with dynamic productions involving two targets and often described as inherently long, is under-studied cross-linguistically (e.g., Petersen, 2018), including within many well-documented languages. Nafsan, an Oceanic language spoken by around 6000 people on Efate island in Vanuatu, has a vowel inventory with monophthongs of five qualities, all with a length contrast (Billington et al., 2021), and at least six contrastive closing diphthongs (Thieberger, 2006). These include /ei/ and /oi/, and two pairs in which the primary difference is viewed as the height of the second target: /ai/ and /ae/, and /au/ and /ao/. However, there are indications that duration may be an important correlate in these pairs. This presentation reports on a study of the six closing diphthongs based on data collected with six Nafsan speakers in Erakor village, using a wordlist of mostly monosyllabic words with diphthongs in both open syllables and syllables closed with a coronal consonant, produced in an utterance-medial frame. Results show that, in addition to differences in second formant frequency, /ae/ and /ao/ are significantly longer than /ai/ and /au/, raising questions about whether the contrast is best interpreted as a length contrast similar to that found among monophthongs.