The present study explores the influence of individual differences in experience, perceptual acuity, and working memory on the development of both declarative and automatized aspects of L2 phonological vocabulary knowledge. A total of 486 Japanese English-as-a-foreign-language (EFL) students took part in two vocabulary tests designed to measure declarative (meaning recognition) and automatized knowledge (lexicosemantic judgement task). Their performance was tied to the quantity and quality of their EFL experience, as well as their scores in auditory processing and working memory. While several significant, modest correlations between experience, aptitude, and vocabulary outcomes were observed, certain predictor variables were uniquely associated with either declarative or automatized vocabulary performance. Specifically, individuals with more extensive, typically language-focused EFL training and greater working memory demonstrated higher levels of declarative knowledge. Conversely, those who pursued extracurricular practice outside the classroom – exposing themselves to auditory materials and/or participating in study-abroad experiences – showed a more automatic execution of vocabulary knowledge.

The last three decades have seen significant development in understanding and describing the effects of task complexity on learner internal processes. However, researchers have primarily employed behavioral methods to investigate task-generated cognitive load. Being the first to adopt neuroimaging to study second language (L2) task effects, we aimed to provide novel insights into the neural correlates of task-related variation in L2 oral production. To advance research methodology, we also tested the utility of a neuroimaging technique, functional magnetic resonance imaging (fMRI), in examining the impact of task-related variables on L2 speech production when combined with cognitive–behavioral tools (speech analysis, expert and learner judgments). Our research focus was the effects of task complexity on silent pausing. Twenty-four Japanese learners of English completed eight simple and complex versions of decision-making tasks, half in their first language and half in their L2. The dataset for the present study included the L2 speech and fMRI data, expert judgments, and participants’ difficulty ratings of the L1 and L2 tasks they completed. Based on our findings, we concluded that brain imaging and L1 task difficulty ratings were more sensitive to detecting task complexity effects than L2 self-ratings and pausing measures. These results point to the benefits of triangulating cognitive and neural data to study task-based neurocognitive processes.

Men who have sex with men (MSM) who use injection drugs (MSM-IDU) are at high risk of sexually transmitted infections (STIs), but the long-term incidence is unclear. We conducted a single-centre retrospective cohort study using the clinical records of non-haemophilia men with human immunodeficiency virus (HIV) who visited the Institute of Medical Science, the University of Tokyo (IMSUT) Hospital, located in Tokyo, Japan, from 2013 to 2022. We analysed 575 patients including 62 heterosexual males and 513 MSM patients, of whom 6.8% (35/513) were injection drug use (IDU). Compared to non-IDU MSM, MSM-IDU had a higher incidence of hepatitis C virus (HCV) (44.8 vs 3.5 /1,000 person-years (PY); incidence rate ratio (IRR) [95% confidence interval (95% CI)], 12.8 [5.5–29.3], p < 0.001) and syphilis (113.8 vs 53.3 /1,000 PY; IRR, 2.1 [1.4–3.1], p < 0.001). The incidence of other symptomatic STIs (amoebiasis, chlamydia, and gonorrhoea infections) was <4/1,000 PY. In multivariable Poisson regression analysis, HCV incidence was associated with MSM (IRR, 1.8 × 106 [9.9 × 105–3.4 × 106], p < 0.001), IDU (IRR, 10.1 [4.0–25.6], p < 0.001), and syphilis infection during the study period (IRR, 25.0 [1.2–518.3]/time/year, p < 0.001). Among men with HIV, the prevalence of IDU in MSM and the long-term incidence of STIs in MSM-IDU were high. IDU and sexual contact are important modes of transmission of HCV among HIV-infected MSM in Tokyo.

The present study revisits the differential roles of form, meaning, and use aspects of phonological vocabulary knowledge in L2 listening proficiency. A total of 126 Japanese English-as-a-foreign-language listeners completed the TOEIC Listening test, working memory and auditory processing tests, the Metacognitive Awareness Listening Questionnaire, and several tasks designed to tap into three broad aspects of phonological vocabulary knowledge: (1) the ability to access phonological forms without any orthographic cues (phonologization), (2) the ability to recognize words regardless of the talker (generalization), and (3) the ability to determine the semantic and collocational appropriateness of words in global contexts in a fast and stable manner (automatization). Whereas the perceptual, cognitive, and metacognitive variables made relatively small contributions to L2 listening proficiency (0.4%–21.3%), the vocabulary factors explained a large amount of the variance (77.6%) in the full regression model (R2 = .507). These large lexical effects uniquely derived from the three different aspects of phonological vocabulary knowledge—automatization (55.3%), phonologization (20.8%), and generalization (1.5%). The findings suggest that successful L2 listening skill acquisition draws on not only various levels of phonological form-meaning mapping (phonologization, generalization) but also the spontaneous and robust retrieval of such vocabulary knowledge in relation to surrounding words (automatization).

In this two-part study, we conducted both cross-sectional and longitudinal investigations on the relative weights of experiential, cognitive, and sociopsychological factors in adult L2 speech learning. In the cross-sectional phase (Study 1), speech was elicited from 73 Japanese speakers of English via a picture description task, and rated for accentedness and comprehensibility. These scores were linked to scores on a range of tests designed to measure aptitude, motivation, and anxiety. The results showed that comprehensibility was exclusively linked to experiential variables (e.g., the amount of L2 use outside classrooms), while accentedness was linked to phonemic coding ability and anxiety. In the longitudinal phase (Study 2), we tracked the same participants' L2 comprehensibility and accentedness development when they received four weeks of explicit pronunciation instruction. According to the results of pre- and post-tests, participants significantly improved the comprehensibility and accentedness of their speech regardless of cognitive and sociopsychological differences.

In this paper, I first provide a brief review of how scholars have conceptualized, tested, and elaborated aptitude frameworks relevant to second language (L2) speech learning. Subsequently, I introduce an emerging paradigm that assigns a fundamental role to domain-general auditory processing (i.e., having a good ear) in L1 speech acquisition and proposes that the same faculty acts as a cornerstone of L2 speech learning (i.e., the Auditory Precision Hypothesis-L2). This hypothesis predicts that learners with more precise auditory processing ability will be able to make the most of every input opportunity, which will result in more advanced L2 speech proficiency. To close, I will provide suggestions on how scholars can assess L2 students’ auditory processing ability (e.g., our team's offline test deposited at L2 Speech Tools for Researchers & Teachers [http://sla-speech-tools.com/]) and discuss how the results can be used to maximize learners’ L2 speech learning opportunities via optimal, profile-matched training programs (e.g., explicit vs. incidental training; naturalistic vs. classroom learning; phonetic vs. auditory training).

This article proposes a conceptual and measurement framework for postpubertal, L2 speech learning aptitude that is centered around domain-general auditory processing (i.e., representing spectral and temporal characteristics of sounds). To this end, we examine the construct and reliability of a battery of auditory processing tests by presenting the results of an empirical study wherein 100 participants took the tests twice. The findings showed (a) that the tasks tapped into multiple dimensions of auditory processing ability (e.g., perceptual acuity, audio-motor integration); and (b) that test-retest reliability ranged from “fair” to “excellent” (ICC (2,2) = .4–.8). Last, we introduce an offline version of the tests (deposited at L2 Speech Tools for Researchers & Teachers; http://sla-speech-tools.com/), provide a brief user manual, and invite researchers to use these tests to examine the role of auditory processing in various aspects of L2 speech learning (naturalistic vs. classroom, perception- vs. production-based practice).

The current study set out to examine to what degree age of acquisition (AOA), defined as a learner’s first intensive exposure to a second language (L2) environment, mediates the final state of postpubertal, spoken vocabulary attainment. In Study 1, spontaneous speech samples were elicited from experienced Japanese users of English (n = 41) using storytelling and interview tasks. The samples were analyzed using a range of corpus- and rater-based lexical measures and compared to the speech of inexperienced Japanese speakers (n = 40) and native speakers of English (n = 10). The results showed that most experienced L2 learners tended to demonstrate nativelike proficiency for relatively easy lexical dimensions of speech (i.e., richness), but that AOA appeared to play a key role in predicting the ultimate attainment of relatively difficult lexical dimensions (i.e., appropriateness). In Study 2, the findings were successfully replicated with experienced L1 Polish users of English (n = 50).

Extending the paradigm in L1 acquisition, scholars have begun to investigate whether participants’ domain-general ability to represent, encode, and integrate spectral and temporal dimensions of sounds (i.e., auditory processing) could be a potential determinant of the outcomes of post-pubertal L2 speech learning. The current study set out to test the hypothesis that auditory processing makes a unique contribution to L2 speech acquisition, for 70 Japanese classroom learners of English with different levels of L2 proficiency when biographical backgrounds (length of instruction and immersion) and memory abilities (working, declarative, and procedural memory) are controlled for. Auditory processing loaded onto modality-general capacities to represent and incorporate anchor stimuli (relative to target stimuli) into long-term memory in an implicit fashion, but dissociated from explicit abilities to remember, associate, and elaborate sensory information. Auditory processing explained a small-to-medium amount of variance in L2 speech learning, even after the other potentially confounding variables were statistically factored out.

Whereas many scholars have emphasized the relative importance of comprehensibility as an ecologically valid goal for L2 speech training, testing, and development, eliciting listeners’ judgments is time-consuming. Following calls for research on more efficient L2 speech rating methods in applied linguistics, and growing attention toward using machine learning on spontaneous unscripted speech in speech engineering, the current study examined the possibility of establishing quick and reliable automated comprehensibility assessments. Orchestrating a set of phonological (maximum posterior probabilities and gaps between L1 and L2 speech), prosodic (pitch and intensity variation), and temporal measures (articulation rate, pause frequency), the regression model significantly predicted how naïve listeners intuitively judged low, mid, high, and nativelike comprehensibility among 100 L1 and L2 speakers’ picture descriptions. The strength of the correlation (r = .823 for machine vs. human ratings) was comparable to naïve listeners’ interrater agreement (r = .760 for humans vs. humans). The findings were successfully replicated when the model was applied to a new dataset of 45 L1 and L2 speakers (r = .827) and tested under a more freely constructed interview task condition (r = .809).

Recently, scholars have begun to explore the hypothesis that individual differences in domain-general auditory perception, which has been identified as an anchor of L1 acquisition, could explain some variance in postpubertal L2 learners’ segmental and suprasegmental learning in immersive settings. The current study set out to examine the generalizability of the topic to the acquisition of higher-level linguistic production skills—that is the appropriate use of diverse, rich, and abstract vocabulary. The speech of 100 Polish-English bilinguals was elicited using an interview task, submitted to corpus-/rater-based linguistic analyses, and linked to their ability to discriminate sounds based on individual acoustic dimensions (pitch, duration, and amplitude). According to the results, those who attained more advanced L2 lexical proficiency demonstrated not only more relevant experience (extensive immersion and earlier age of arrival), but also more precise auditory perception ability.

Eighty Japanese learners of English as a foreign language encountered 40 target words in one of four experimental conditions (three encounters, six encounters, three encounters with talker variability, and six encounters with talker variability). A picture-naming test was conducted three times (pretest, immediate posttest, and delayed posttest) and elicited speech samples were scored in terms of form-meaning connection (spoken form recall) and word stress accuracy (stress placement accuracy and vowel duration ratio). Results suggested that frequency of exposure consistently promoted the recall of spoken forms, whereas talker variability was more closely related to the enhancement of word stress accuracy. These findings shed light on how input quantity (frequency) and quality (variability) affect different stages of lexical development and provide implications for vocabulary teaching.

Precise auditory perception at a subcortical level (neural representation and encoding of sound) has been suggested as a form of implicit L2 aptitude in naturalistic settings. Emerging evidence suggests that such implicit aptitude explains some variance in L2 speech perception and production among adult learners with different first language backgrounds and immersion experience. By examining 46 Chinese learners of English, the current study longitudinally investigated the extent to which explicit and implicit auditory processing ability could predict L2 segmental and prosody acquisition over a 5-month early immersion. According to the results, participants’ L2 gains were associated with more explicit and integrative auditory processing ability (remembering and reproducing music sequences), while the role of implicit, preconscious perception appeared to be negligible at the initial stage of postpubertal L2 speech learning.

In this study, we propose a hypothesis that domain-general auditory processing, a perceptual anchor of L1 acquisition, can serve as the foundation of successful post-pubertal L2 learning. This hypothesis was tested with 139 post-pubertal L2 immersion learners by linking individual differences in auditory discrimination across multiple acoustic dimensions to the segmental, prosodic, lexical, and morphosyntactic dimensions of L2 proficiency. Overall, auditory processing was a primary determinant of a range of participants’ proficiency scores, even after biographical factors (experience, age) were controlled for. The link between audition and proficiency was especially clear for L2 learners who had passed beyond the initial phase of immersion (length of residence > 1 year). The findings suggest that greater auditory processing skill benefits post-pubertal L2 learners immersed in naturalistic settings for a sufficient period of time by allowing them to better utilize received input, which results in greater language gains and leads to more advanced L2 proficiency in the long run (similar to L1 acquisition).

In this study, we propose a hypothesis that domain-general auditory processing, a perceptual–cognitive anchor of first language (L1) acquisition, can serve as an important deciding factor for successful postpubertal second language (L2) pronunciation learning. To examine this hypothesis, samples of spontaneous speech were elicited from a total of 30 L1 Chinese L2 English learners at two points (outset and endpoint) during an 8-month study-abroad period in the United Kingdom. The participants were tested on three different components of auditory processing ability (formant, pitch, and duration discrimination) using behavioral instruments. The auditory processing scores were then linked to the segmental, prosodic, and fluency dimensions of their L2 pronunciation proficiency development throughout the project. Overall, most learners’ speech became smoother, faster, and more fluent (fewer pauses, faster articulation rate, and more optimal perceived tempo). Certain learners with high-level auditory processing ability (more precise formant discrimination) appeared to further attain more correct pronunciation of individual sounds and words (greater segmental and word stress accuracy), leading to more advanced L2 phonological skills (fluent and accurate). The findings suggest that auditory processing abilities can be a root of language learning throughout the life span and may apply to the initial- to midphase of naturalistic L2 pronunciation learning in adulthood.

Following the trends established in psychology and emerging in L2 research, we explain our support for an Open Science approach in this paper (i.e., developing, analyzing and sharing datasets) as a way to answer controversial and complex questions in applied linguistics. We illustrate this with a focus on a frequently debated question, what underlies individual differences in the dynamic system of post-pubertal L2 speech learning? We provide a detailed description of our dataset which consists of spontaneous speech samples, elicited from 110 late L2 speakers in the UK with diverse linguistic, experiential and sociopsychological backgrounds, rated by ten L1 English listeners for comprehensibility and nativelikeness. We explain how we examined the source of individual differences by linking different levels of L2 speech performance to a range of learner-extrinsic and intrinsic variables related to first language backgrounds, age, experience, motivation, awareness, and attitudes using a series of factor and Bayesian mixed-effects ordinal regression analyses. We conclude with a range of suggestions for the fields of applied linguistics and SLA, including the use of Bayesian methods in analyzing multivariate, multifactorial data of this kind, and advocating for publicly available datasets. In keeping with recommendations for increasing openness of the field, we invite readers to rethink and redo our analyses and interpretations from multiple angles by making our dataset and coding publicly available as part of our 40th anniversary ARAL article.

For a character of the absolute Galois group of a complete discrete valuation field, we define a lifting of the refined Swan conductor, using higher dimensional class field theory.

The current study examines how second language (L2) users differentially assess the comprehensibility (i.e., ease of understanding) of foreign-accented speech according to a range of background variables, including first language (L1) profiles, L2 proficiency, age, experience, familiarity, and metacognition. A total of 110 L2 listeners first evaluated the global comprehensibility of 50 spontaneous speech samples produced by low-, mid-, and high-proficiency Japanese speakers of English. The listeners were categorized into two subgroups according to a cluster analysis of their rating scores: lenient and strict. Results showed that while the lenient listeners appeared to rely equally on many linguistic areas of speech during their judgments, the strict listeners were strongly attuned to phonological accuracy. Analysis of the background questionnaire data revealed that more lenient listeners likely had higher levels of awareness of the importance of comprehensibility for communication (metacognition); regularly used L2 English in professional settings (experience); and had L1s more linguistically close to the target speech samples, Japanese-accented English (L1-L2 distance).