Speakers coarticulate less in response to both real and imagined communicative challenges: An acoustic analysis of the LUCID corpus

Overlap of adjacent articulatory gestures leads to coarticulation. Understanding how hyperarticulated intelligibility-enhancing clear speech modifications affect coarticulation can inform theories of phonetic variation and speech intelligibility. However, prior research yielded mixed findings regarding the relationship between hyperarticulation and coarticulatory patterns. This study extends previous work by analyzing the degree of coarticulation across several different communicative conditions in the LUCID corpus (Baker & Hazan, 2010). Southern British English speakers completed an interactive spot-the-difference task with a partner with and without a communicative barrier (e.g., speech degraded by talker babble). They also read sentences without an interlocutor casually and clearly. Diphones in keywords produced in both tasks were analyzed using two whole-spectrum measures, with greater spectral distance and shorter coarticulatory overlap between the diphones indexing less coarticulation. Results revealed that speakers coarticulated less in response to both real (interactive task) and imaginary (sentence-reading) communicative challenges. Speakers furthermore varied the degree of coarticulatory resistance in different real communicative barriers. Diphones with greater consonant articulatory constraint were less sensitive to differences between the conditions, suggesting a limit to the hyperarticulation-induced phonetic variation. The findings agree with the models of targeted speaker adaptations assuming coarticulatory resistance in hyperarticulated clear speech (the H&H theory: Lindblom, 1990).