This study investigated L2 Korean speakers' self-assessment of speech comprehensibility and accentedness, including a conceptual replication of Trofimovich, Isaacs, Kennedy, Saito, and Crowther (2016, Experiment 1) and exploratory analyses of individual differences in self-assessment. L2 Korean speakers (N = 198) self-assessed their…

This study longitudinally examined the effects of cognitive and sociopsychological individual differences (aptitude, motivation, personality) and the quantity and quality of second language (L2) experience on L2 speech gains in naturalistic settings. We elicited L2 spontaneous speech from 50 Chinese learners of English at the beginning and the end…

Some listeners exhibit higher sensitivity to subphonemic acoustic differences (i.e., higher speech gradiency). Here, we asked whether higher gradiency in a listener's first language (L1) facilitates foreign language learning and explored the possible sources of individual differences in L1 gradiency. To address these questions, we tested 164…

This article focuses on a theoretical and empirical exploration of developmental trajectories and individual learner variation in second language (L2) acquisition. Taking a processability perspective, I view learner language as a dynamic system that includes predictable universal developmental trajectories as well as individual learner variation,…

In bilinguals and second language learners, the native (L1) and nonnative (L2) languages coexist and interact. The L1 influences L2 production via forward transfer, as is seen with foreign accents. However, language transfer is bidirectional: even brief experience with an L2 can affect L1 production, via backward transfer. Here, we review the…

This study investigates acquisition of second language (L2) vocabulary from reading a connected authentic text. Advanced and upper-intermediate L2 (English) participants read a long expository text for general understanding, with embedded critical vocabulary items (pseudowords). Explicit knowledge of the critical items was examined using a meaning…

In the process of language learning, individuals must acquire different types of linguistic knowledge, such as the sounds of the language (phonemes), how these may be combined to form words (phonotactics), and morphological rules. Early and late bilinguals tend to perform like natives on second language phonological tasks that involve pre-lexical…

Many learners of a foreign language (L2) struggle to correctly pronounce newly learned speech sounds, yet many others achieve this with apparent ease. Here we explored how a training study of learning complex consonant clusters at the very onset of L2 acquisition can inform us about L2 learning in general and individual differences in particular.…

The Foreign Language Classroom Anxiety Scale (FLCAS) has been challenged on the grounds that it may also assess language learning skills. In this study, 128 students who had been administered measures of first language (L1) skills in elementary school were followed from 1st to 10th grade. Fifty-three students had completed second language (L2)…

Variability in achievement across learners is a hallmark of second language (L2) learning, especially in academic-based learning. The Twins Early Development Study (TEDS), based on a large, population-representative sample in the United Kingdom, provides the first opportunity to examine individual differences in second language achievement in a…

In this article, I describe studies conducted over 25 years with secondary and post-secondary L2 learners in the United States. The evidence from these studies shows that there are important connections between students' early L1 skills and their L2 aptitude and L2 proficiency and that individual differences in students' L1 skills in elementary…

The study examined whether individual differences in high school first language (L1) reading achievement and print exposure would account for unique variance in second language (L2) written (word decoding, spelling, writing, reading comprehension) and oral (listening/speaking) proficiency after adjusting for the effects of early L1 literacy and…