Here are some of our research topics and selected publications relating to each topic.

We investigate the articulatory and acoustic characteristics of language learners’ speech productions.
One of the central goals in the field of phonological acquisition is to determine what language learners know about the sound structures of the target language and how this knowledge changes over time. To gain a better understanding of these, we study when and how language learners acquire various articulatory and acoustic cues to phonemic contrasts.

• Song, J.Y.& Eckman, F.R. (2021). Using ultrasound tongue imaging to study covert contrastsin second-language learners’ acquisition of English vowels. Language Acquisition, 28(4), 344-369.
• Song, J.Y., Shattuck-Hufnagel, S., & Demuth, K. (2015). Development of phonetic variants (allophones) in 2-year-olds learning American English: A study of alveolar stop /t, d/ codas. Journal of Phonetics, 52, 152-169.

We study mechanisms involved in both first- and second-language acquisition.
Despite the rich literature in L1 and L2 acquisition studies, there is a lack of communication between the two disciplines. In an attempt to narrow the gap in our understanding of the L1 and L2 acquisition, our research projects have examined some general learning mechanisms that are involved in both, including (1) hypercorrection, a stage in which some learners make errors by over-correcting, and (2) covert contrast, a stage in which some learners produce a statistically reliable distinction between target sounds, but do so in a way that is not perceived by listeners.

• Song, J.Y. & Eckman, F.R. (2019). Covert contrasts in the acquisition of English high front vowels by native speakers of Korean, Portuguese and Spanish. Language Acquisition. Language Acquisition.
• Eckman, F.R., Iverson, G.K., & Song, J.Y. (2013). The role of hypercorrection in the acquisition of L2 phonemic contrasts. Second Language Research, 29(3), 257-283.

We study the role of language input in language acquisition.
It is easy to find substantial individual differences among language learners. To study the role of language input in explaining individual variability, we have looked at the effects of both child-directed speech in L1 acquisition and perceptual training in L2 acquisition. Furthermore, we have extended our expertise in child-directed speech to study the articulatory and acoustic properties of clearly enunciated vowels.

• Song, J.Y., Demuth, K., & Morgan, J. (2018). Input and processing factors affecting infants’ vocabulary size at 19 and 25 months. Frontiers in Psychology, 9, 2398.
• Song, J.Y. (2017). The use of ultrasound in the study of articulatory properties of vowels in clear speech. Clinical Linguistics & Phonetics, 31(5), 351-374.
• Song, J.Y., Demuth, K., & Morgan, J.L. (2010). Effects of the acoustic properties of infant-directed speech on infant word recognition. Journal of the Acoustical Society of America, 128(1), 389-400.