Acoustic and perceptual effects of vowel length on voice onset time in Thai stops

Abstract

In Thai, vowel length (e.g., [pan]-[paan]) and unaspirated–aspirated stop (e.g., [pan]-[phan]) distinctions are contrastive; this study examines possible acoustic and perceptual interactions between these temporal properties. VOT and vowel duration were measured for five repetitions of 40 (near-) minimal word pairs beginning with aspirated or unaspirated bilabial, alveolar, or velar stops followed by long or short vowels, produced by three native Thai speakers. Although VOT for velars was slightly longer (about 5 ms) before long than before short vowels, the overall acoustic picture across places of articulation showed no systematic effect of vowel length. To test for perceptual influences of contrastive vowel length on VOT, a 15-step 0–90 ms VOT continuum was created by editing the aspiration portion of naturally produced [phaan]. The VOT continuum was spliced onto the vowel portion of four different natural tokens, [pan], [paan], [phan], and [phaan], creating four continua, two with long vowels and two with short. Identification tests were presented to 18 native Thai listeners. Responses to the continua created from the originally unaspirated tokens ([pan], [paan]) showed robust effects of vowel length: the long vowel continuum elicited more aspirated ([ph]) responses. A compensatory account of the perceptual findings is offered. [Work supported by NSF.]