Voicing of glottal consonants and non-modal vowels

Variation in voicing is common among sounds of the world’s languages: sounds that are analyzed as voiceless can undergo voicing, and those analyzed as voiced can devoice. Among voiceless glottal sounds in particular, voicing is widespread: linguists often expect the voiceless glottal stop [ʔ] and fricative [h] to be fully voiced, especially between vowels. In this study, we use audio recordings from Illustrations of the International Phonetic Alphabet published in the Journal of the International Phonetic Association to explore the extent to which glottal consonants and non-modal (breathy and creaky) vowels differ in terms of percentage voicing and voicing intensity in three phrasal positions. We find that voiceless [h] is only slightly less voiced than voiced [ɦ] in initial position. Between two vowels, both [h] and [ɦ] are as voiced as breathy vowels. Glottal stops and creaky vowels are both characterized by high percentages of voicing, but they differ in voicing intensity: in all phrasal positions, glottal stops generally have periods of strong and weak voicing, whereas creaky vowels are strongly voiced. In contrast, vowels described as ‘rearticulated’, ‘checked’, or ‘glottalized’ show similar drops in voicing intensity to glottal stops. We interpret these results through an articulatory lens: glottal consonants and non-modal vowels are both modulations in phonation resulting from laryngeal constriction and vocal fold spreading. We argue further that, because voicing during [ʔ] and [h] is largely predictable from respiratory and prosodic constraints, many cases of [ʔ] and [h] can be considered phonetically underspecified for voicing.