My research primarily focuses on how non-native speakers acquire and process second language (L2) speech, with a particular emphasis on psycholinguistic approaches. My doctoral dissertation investigated how individual differences in the precision of second language phonetic category formation influence second language learning. Currently, I investigate individual differences in L2 speech learning and processing, exploring the dynamic relationship between speech perception and production. Additionally, I am actively involved in developing an ultrasound corpus of non-native speakers at the SNU Multilingual Phonetics Lab.