Reduction patterns of Korean diphthongs across different speech rates*

This study investigates how Korean diphthongs are realized as a function of speech rate and examines which components constitute their core elements. To this end, speakers of the Seoul dialect were asked to read sentences containing word-initial diphthongs at two speech rates: normal and fast. Three components of diphthong realization were analyzed: the glide, the following nucleus vowel, and the transition between them, measured in terms of the F2 slope. The results showed that for j-glide diphthongs, the glide was realized stably regardless of speech rate, whereas the nucleus vowel and the F2 slope exhibited significant differences across speech rates. In contrast, w-glide diphthongs displayed a stable F2 slope across speech rates, while both the glide and the nucleus vowel varied significantly as a function of speech rate. These findings suggest that in j-glide diphthongs, the glide target point constitutes the core component of diphthong realization, whereas in w-glide diphthongs, the F2 slope, rather than the target points, plays a more central role. Overall, the results indicate that diphthong realization under different speech-rate conditions cannot be accounted for by a single articulatory pattern. Instead, even within a single language, diphthongs may be realized through different articulatory control strategies.