Korean ESL Learners’ Production of English Vowel Contrasts: Developmental Variations in L2 Sound Learning

The present study elucidates the developmental progression of English vowel production in Korean learners’ L2 speech. The study focused on the first and second formant frequencies and duration values of seven American English monophthongs (excluding /u, ʊ, ə/) produced by Korean adults classified into three groups according to their proficiency in pronunciation (the degree of foreign accent): low, intermediate, and high. Then we compared them with those produced by native speakers. Results showed between-group differences in that high ESL learners produced English vowel contrasts by using spectral and/or temporal cues in a way resembling the native speakers’, while intermediate and low groups were relatively more limited in using these cues. The study also observed differences in the production of front and back vowels among ESL learners. Specifically, high learners primarily relied on temporal rather than spectral characteristics in producing back vowel contrasts, whereas intermediate and low learners showed no significant distinctions in temporal or spectral dimensions of back vowels. These results highlight the complex developmental processes involved in second language (L2) vowel learning.