Effects of Word Stress on Vowel Duration and Vowel Quality in the Speech of Korean Learners of English

Abstract

Unstressed English vowels are reduced in their durational and spectral aspects. Vowel reduction in relation to word stress in English has been one of the challenges faced by Korean learners of English in learning English vowel system. In this study, we investigated effects of word stress on the vowel duration and vowel quality. This study focused on two unstressed vowels (/ə/ and /ɪ/) and three stressed vowels (/ʌ/, /ɪ/, and /i/). Words with five target vowels in the first syllable of word were collected from sentences produced by two subject groups. Vowel durations and first and second formant values were calculated and analyzed for the effect of stress which interplayed with intrinsic vowel duration and vowel quality. Study results indicated that speech data of Korean learners of English had much less magnitude in vowel shortening and reduction of vowel quality in unstressed vowels than those of English speakers. In addition, the five target vowels tended to be grouped into two in vowel space for Korean learners of English. Pedagogical implications of this study are discussed to improve learning and teaching English vowel system for Korean learners of English.