English Vowel Reduction by Korean Learners

English unstressed reduced vowels, such as schwa '[ə]' and barred-i '[ɨ]', have phonetic features that are distinct from other vowels. Phonetic features of those vowels are reduced in duration and vowel quality (F1 and F2). Schwa '[ə]' occurs in a word-final position like Rosa as a mid central reduced vowel and barred-i '[ɨ]' occurs in a non-final position like roses as a high central reduced vowel (Flemming & Johnson 2007). In contrast to English, there is no stress in Korean phonological system and thus stress-related vowel reduction phenomenon does not arise in Korean. Moreover, '/ə/' and '/ɨ/' that are similar to English unstressed vowels ([ə], [ɨ]) exist as full vowels in Korean. This different prosodic system provides Korean learners of English with difficulty to accurately produce English unstressed vowels (McAllister, Fledge, & Piske 2002).
The aim of this paper is three fold. The first is to see whether English unstressed reduced vowels spoken by Korean speakers are different from those spoken by native speakers in terms of schwa '[ə]'. The second is to see whether English unstressed reduced vowels spoken by Korean speakers are different from those spoken by native speakers in terms of barred-i '[ɨ]'. The third is to investigate the gap of the mean duration between stressed and unstressed vowels produced by native and Korean speakers. For the analysis, four native speakers of American English and twelve native speakers of Korean participated in this experiment. The number of data is 57 and all subjects read data with three repetitions in a carrier phrase. This experiment yielded 2736 observations (16 subjects * 57 words * 3 repetitions).
The results showed that Korean speakers were not nativelike in English vowel reduction. As for schwa, native speakers produced unstressed reduced vowels in a word-final position in mid central reduced way, while unstressed vowels in this position spoken by Korean learners of English speakers were widely dispersed in vowel space and not reduced in nativelike way. As for barred-i, native speakers produced unstressed vowels in a non-final position in high central reduced way. However, unstressed vowels produced by Korean learners of English were not reduced in nativelike way, with small dispersion. This is because Korean speakers tended to produce unstressed vowels, spelled 'e', similarly with high front vowel '/i/'. Even unstressed vowels, spelled 'a', realized nearly as low back vowel '/ɑ/' for Korean beginners of English. Korean learners also made less difference in duration between stressed and unstressed vowels than native speakers, suggesting that Korean learners had longer duration for reduced vowels than native speakers. These results supported the evidence that Korean learners of English have difficulty in acquiring phonetic features of English vowel reduction, basically ascribable to stress.