How does coarticulation play a role at the end of a sound change? A dynamic-acoustic study of historical ł-vocalization in the Polish film chronicle (1944–1994)

This study presents a real-time acoustic-dynamic analysis of ł-vocalisation in Polish newsreel speech broadcast between 1944 and 1994. Using a 150,000-token dataset, we examined three phonetic variants—[ł], [Ł] (reduced velarised lateral), and [w]—in postconsonantal onset (C/V), intervocalic onset (V/V), and postvocalic coda (V/C) positions, across three recording periods. We measured F2-F1 trajectories as a proxy for acoustic darkness, modelled using Generalised Additive Mixed Models (GAMMs) as a function of time, adjacent phonetic context, lexical stress, sequence duration, and lexical frequency. Results confirm a diachronic shift from the initial [ł, Ł, w] system to a reduced [(Ł), w] system, with the change progressing fastest in V/C position and latest in C/V position, with V/V position showing signs of an earlier merger of phonetic variants than in C/V position. Across all positions, darker variants were favoured adjacent to /ɔ, u/, while the influence of adjacent consonants proved more Polish-specific, with labial and velar consonants not yielding darker lateral realisations, contrary to findings from prior English-language studies. Our findings demonstrate that, in the lenition of [ł] at its very late stages through to completion, the sound change continues to be shaped by the position of the segment within the syllable, but without being driven by the coarticulatory factors that typically initiate earlier stages, namely the influence of the adjacent segment.