Coarticulation across word boundaries and its role in L2 English accentedness

L2 learners gradually acquire accurate segmental production and appropriate word boundary coarticulation. Even when segmental accuracy is high, differences in interword articulation may still influence perceived accentedness. This pilot study tested a protocol for examining whether word-boundary consonant errors and speech rate relate to perceived accentedness in L2 English. Six adult L2 speakers (L1s: Mandarin, Thai, Finnish) and one native control completed a phrase-repetition task and read two longer passages aloud. Word-boundary consonant errors were identified using combined audio and lingual-ultrasound analysis. Two expert listeners independently ranked speakers by accentedness, and speech rate was measured relative to a native model. Strong positive correlations emerged between accentedness and both the frequency of word-boundary errors (r = .96) and overall speech duration (r = .95). Highly accented speech showed coda omissions, voicing errors, assimilations, and increased variability across repetitions, particularly in clusters and stops with shared places of articulation. Slower speech with hesitations at word boundaries also aligned with higher accentedness ratings. These findings suggest that word-boundary articulation and speech rate may offer useful objective indicators of L2 pronunciation proficiency and highlight the instructional value of targeting coarticulation and linking words to phrases.