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Paper short abstract

This study examines how vowel duration affects the intelligibility and accentedness of Japanese produced by Polish speakers. Using PSOLA manipulations and native listener evaluations, results show that correcting vowel length significantly improves both intelligibility and accent ratings.

Paper long abstract

This study investigates the role of vowel duration in the phonemic contrast between short and long vowels in Japanese. Nine native Polish speakers produced minimal pairs differing only in vowel length. Using the PSOLA function in Praat, these recordings were manipulated to match native Japanese vowel durations. Both unmanipulated and manipulated stimuli were then used in a perception experiment hosted on the Gorilla Experiment Builder.

Twenty-four native Japanese listeners completed two tasks: an intelligibility task (four-alternative forced-choice) and an accentedness task (7-point Likert scale). The experiment included 120 test trials and 30 filler items from native Japanese speakers.

Initial acoustic analysis revealed that Polish speakers generally produced both short and long vowels with durations exceeding native norms. While most preserved the short-to-long ratio, some speakers exhibited ratios that were either too small or too large.

Statistical analysis using a logistic regression model for the intelligibility task showed that adjusting vowel durations to native-like realizations significantly increased accuracy from 72% in the unmanipulated condition to 89% in the manipulated condition. For accentedness, a linear mixed-effects model revealed that duration manipulation predicted a significant 0.5-point increase on the Likert scale.

These findings suggest that while vowel duration is a primary cue for word recognition, it also serves as a significant marker of nativeness. The study contributes to the literature on L2 speech perception and highlights the necessity of prioritizing temporal accuracy in Japanese pronunciation pedagogy for Polish learners.