An inquiry into the relation between the speech style and the speech production of learners of Japanese as a second language

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It is well known that Japanese long vowels are difficult for learners of Japanese as a second language, Expressions like "double-length", "two beats" or the like are found in Japanese textbooks. In actual speech, however, length of some long vowels is shortened and they sound like short vowels. In this resarch, we describe preliminary research of the long-vowel-shortening phenomena which was carried out using three different research methods.First, we analyzed acoustically recordings of native speakers reading sentences written on cards and found that long-vowel-shortening did not occur. Then we analyzed a recording of spontaneous conversation and found out that long-vowel-shortening was more likely to occur at non-word-initial positions than at word-initial-positions. Lastly we prepared synthesized sentences in which vowel length was controlled in ten stages and carried out a categorical perception test. The results indicated that native speakers of Japanese have less keen sense of vowel shortening at non-word-initial positions than at word-initial positions.