Enhancement effects of clear speech and word-initial position in Korean glides.

The current study investigated the enhancement effect in Korean speakers' clear speech and word-initial position, using acoustic analyses of the Korean glides /w/ and /j/. The results showed that the transitions of glides /w/ and /j/ at onset were enhanced in clear speech with an expanded vowel space. An expanded vowel space was also observed in the word-initial position, but the expansion was not statistically significant. However, the significant interaction between speaking style and word position revealed that the articulatory and global modifications in clear speech were noticeably greater at onset in the word-medial compared to the word-initial position. Also, the mid-front vowel /e/ shifted downward and leftward in clear speech, indicating that mid-front vowels are fronted and lowered in clear speech. As a language-specific issue, no phonetic evidence was found supporting the existence of two Korean glides, /wε/ and /we/, even in clear speech and word-initial position, indicating a diachronic sound merger of these two glides. In addition, the glide /je/ after a consonant was neutralized into /e/ in casual speech. These findings suggest a relationship between speaking style effects, word position effects, and changing phonetic targets due to diachronic sound change.