Categorical or gradient? An ultrasound investigation of /l/-darkening and vocalization in varieties of English

This paper presents an empirical analysis of /l/-darkening in English, using ultrasound tongue imaging data from five varieties spoken in the UK. The analysis of near 500 tokens from five participants provides hitherto absent instrumental evidence demonstrating that speakers may display both categorical allophony of light and dark variants, and gradient phonetic effects coexisting in the same grammar. Results are interpreted through the modular architecture of the life cycle of phonological processes, whereby a phonological rule starts its life as a phonetically driven gradient process, over time stabilizing into a phonological process at the phrase level, and advancing through the grammar. Not only does the life cycle make predictions about application at different levels of the grammar, it also predicts that stabilized phonological rules do not replace the phonetic processes from which they emerge, but typically coexist with them, a pattern which is supported in the data. Overall, this paper demonstrates that variation in English /l/ realization has been underestimated in the existing literature, and that we can observe phonetic, phonological, and morphosyntactic conditioning when accounting for a representative range of phonological environments across varieties.