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

Abstract

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.

North American /l/ both darkens and lightens depending on morphological constituency and segmental context

“…This provides support for the methodological choice of previous studies which have used duration of a preceding vowel and /l/ rather than the /l/ alone, even in cases where the vowel and /l/ are not syllabified together (e.g., Sproat & Fujimura, 1993;Turton, 2014Turton, , 2017. We will therefore follow these precedents and use the rhyme for duration measures in our analysis.…”

“…Following Sproat and Fujimura (1993), a number of works argue that light and dark /l/ are points on a phonetic continuum of /l/-darkness, rather than categorically distinct allophones (e.g., Huffman, 1997;Lee-Kim et al, 2013). Others, however, argue that a categorical distinction between dark and light /l/ coexists with gradient effects on /l/-darkness (e.g., Scobbie & Pouplier, 2010;Yuan & Liberman, 2011a;Bermúdez-Otero & Trousdale, 2012;Turton, 2014Turton, , 2017.…”

“…This is in contrast to the RP, Manchester, and Middlesbrough speakers included in the study who show no evidence of morphological effects but display varying degrees of coda and phrase-final darkening. Although this experiment did not include the word-internal, morpheme-initial environment (e.g., free-ly) this context was included in Experiment 2 of Turton (2014), also reported in Turton (2017). This experiment was designed primarily to determine whether variation in /l/-darkness shows evidence of a gradient or categorical distribution across a range of contexts and does not focus on minimal comparison of environments which differ in the position of /l/ relative to morphological boundaries.…”

“…However, attempts to control for these effects in experimental stimuli have been shaped by a priori assumptions that /l/-darkening is the appropriate phonological analysis. Many studies have intentionally used items in which /l/s are adjacent to front vowels because of the expectation that /l/-darkening will be most apparent in this environment (e.g., Sproat & Fujimura, 1993;Scobbie & Pouplier, 2010;Turton, 2014Turton, , 2017. While we also found effects of /l/-darkening in the context of a following high vowel (e.g., free-ly, meal-y, Healey) we found effects of morpheme-initial /l/-lightening in the context of a following reduced vowel (e.g., real-est, knee-less, velum).…”

“…There was substantial variation in the magnitude of the distinction between speakers, leading them to conclude that the morphological boundary conditions gradient phonetic differences rather than alternations of categorically distinct allophones, at least for some speakers (Strycharczuk & Scobbie, 2016, p. 90). Turton's (2014Turton's ( , 2017 crossdialectal study looks at articulatory and acoustic data from /l/s in a number of morphosyntactic environments. Data from ultrasound imaging in Experiment 1 of Turton (2014) provides evidence for an effect of morphological boundaries on /l/-darkness for speakers of Essex and American English.…”