Ultrasound production training of Amercian English retroflex /ɹ/: A case of Korean L2 learners

This study investigates the efficacy of ultrasound tongue imaging as a tool for training Koreanlearners of English in producing the American English retroflex /ɹ/. Due to the absenceof a direct equivalent of /ɹ/ in Korean and the complex phonetic relationship betweenKorean and English liquid sounds, Korean learners often struggle with accurateproduction. In the experiment, nine Korean participants of intermediate-level proficiencywere trained to produce American English retroflex /ɹ/. Ultrasound imaging wasemployed to provide real-time visual feedback on tongue movements, aiming to enhancethe articulatory accuracy of both onset and coda variants. Participants underwent sixtraining sessions over three weeks, and results revealed significant improvements inarticulatory accuracy after the training, particularly in tongue tip elevation and dorsumlowering. Also, these improvements were sustained a month later, indicating effectivegeneralization. This suggests that ultrasound feedback can successfully facilitate thelearning of complex L2 sounds like the English retroflex /ɹ/. In addition, there wasa notable asymmetry in the learning process between onset and coda retroflex allophones,with the coda variant ([ɹ]) being acquired more readily than the onset variant ([ɹw]). This discrepancy is attributed to the greater phonetic dissimilarity between the KoreanL1 [l] and the English L2 [ɹ] in coda positions, compared to the dissimilarity between[ɾ] and [ɹw] in onset positions. This finding suggests that Korean learners are likelyto acquire the coda variant earlier than the onset variant in their learning developmentof the English L2 retroflex.