Acoustic and Articulatory Characteristics of English Semivowels /ɹ, l, w/ Produced by Adult Second-Language Speakers.

The findings provide acoustic and kinematic evidence for challenges that L2 speakers experience in the production of English semivowels, especially /ɹ/ and /w/. The robust and consistent finding of reduced contrasts among semivowels and their correlations with perceptual accent ratings suggests using sound contrasts as a potentially effective approach to accent modification paradigms.