Acquisition of English Sentence Stress by Korean EFL Learners

This paper investigates the acquisition of English stress in the production of English texts by adult Korean EFL learners. The data was collected from 63 speakers (55 Korean speakers at an intermediate level and eight native speakers of American English) and 14,336 tokens were measured and analyzed with regard to differences between the stressed vowels and the unstressed ones in terms of the acoustic features: F0, intensity, and duration. In general, the patterns of stressed and unstressed vowels produced by the Korean speakers were similar to the patterns of the native speakers, even though ratios differed. Among the three acoustic features, the learners depended more on duration and intensity than on F0 in manifesting stressed and unstressed vowels. While F0 is expected to be higher for stressed and lower for unstressed, the average F0 of unstressed vowels was even higher than stressed vowels for the American group. As for duration and intensity, both Korean and American speakers showed a significant difference between stressed and unstressed vowels. However, the duration ratio between stressed and unstressed vowels for American male speakers was significantly higher than for the Korean male speakers, whereas there was no significant ratio difference between the female groups. It appeared that there was a significant intensity ratio difference between the American and Korean speakers. This study also attempted to uncover the degree of the reduction of function words. Native speakers seem to reduce all the function words to a relatively similar degree. In contrast, Korean speakers treated individual function words more differently in reduction. This study provides evidence for some of the controversial findings of previous studies about the relative role of F0 in speech, which is not readily available when looking at words at the sentence level.