Non-native Japanese speakers often mispronounce Japanese singleton and geminate stops. Previous studies have pointed out that non-native speakers' mispronunciations are caused by an inadequate closure duration, which is the primary acoustic cue to distinguish singleton and geminate stops. However, the durations of preceding and following segments of the closure have not been fully investigated. In this study, the durations of the closure and the preceding and following consonantvowel segments were analyzed to clarify the characteristics of Japanese singleton and geminate stops mispronounced by Korean and Taiwanese Mandarin speakers. The results revealed that the non-native speakers pronounced singleton stops with a longer closure and a shorter preceding consonant-vowel segment than the native Japanese speakers. In contrast, they pronounced geminate stops with a shorter closure and a longer following consonant-vowel segment than the native Japanese speakers. These results indicate that non-native speakers' mispronunciations of Japanese singleton and geminate stops are caused by both inadequate closure duration and anteroposterior segment durations. It is likely that the reason for the mispronunciation is the difference in the rhythmic unit between Japanese and the first languages of the non-native speakers.
To determine the best acoustic variables to discriminate the affricate [ts] and fricative [s], word materials produced by single-and multi-Japanese speakers were analyzed. An intensity envelope of a rise, steady, and decay part of [ts] and [s] was respectively approximated by a linear line with positive, zero, and negative slopes, and duration of the each part was measured manually and automatically. Discriminant analyses gave the smallest discriminant error with a combination of a rise part duration and sum of a steady and decay part duration in all combinations of methods for measuring duration (manual and automatic) and speakers of word materials (single and multi). This result strongly suggests that the best variables to discriminate the affricate [ts] and fricative [s] are a combination of the rise duration and the sum of steady and decay durations.
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