"I mean ship not sheep ": Intelligibility-based phonetic adaptation in native-nonnative conversation

During native-nonnative interactions, speakers often need to adjust their speech to promote understanding. This study investigates how native and nonnative speakers adapt their speech during real-time conversation to resolve miscommunications stemming from phonemic confusions between English tense- and lax-vowel words (e.g., sheep versus ship). Native English-nonnative (Japanese or Mandarin) speaker dyads completed an unscripted, computer game-based task designed to create intelligibility challenges involving vowel tensity contrasts absent in Japanese and Mandarin. Acoustic analyses (F1, F2, duration) tracked vowel production changes throughout the interaction. Results reveal mutual phonetic adaptation, with both native and nonnative interlocutors enhancing vowel contrasts by shifting their L1-based cue-weighting strategies (spectral versus temporal) to better align with their partner’s patterns. However, in a post-conversation word-reading task, speakers reverted to their original productions, suggesting that adaptations were driven by immediate communicative needs. Additional analyses examine how dyads resolved miscommunications tied to each target word, further establishing the intelligibility-driven nature of these adaptations. Findings underscore a dynamic, collaborative, and goal-oriented process of phonetic adaptation in cross-linguistic interaction, where both native and nonnative speakers strategically modify their speech to improve shared intelligibility.