Abstract

Vocabulary acquisition remains a central challenge for Japanese EFL learners, who often have limited opportunity for incidental exposure to English outside the classroom. Online vocabulary learning platforms, which increasingly draw on autonomous learning principles, data-driven word analysis, and spaced repetition, offer a promising way to support vocabulary study, but questions remain about how such platforms are used within course curricula and about the nature of the vocabulary learners choose to study when given autonomy over their own word lists. This study examines usage and word-selection patterns among 188 students in a general English course at a Japanese national university, drawn from nine academic departments, in which an online vocabulary learning platform was provided as a supplementary resource over an eight-week period and participation was incorporated into course grading. Drawing on platform analytics, the study examines the relationship between students' engagement and their graded participation, and the relationship between the source of students' self-selected texts (e.g., academic, news, encyclopedia) and the academic-department alignment and difficulty level of the vocabulary they chose to study. Findings indicate that graded engagement produced meaningful but uneven participation across departments; that students overwhelmingly selected news media over academic or field-specific texts; and that the resulting vocabulary was concentrated in high-frequency bands, with department-aligned word choice emerging primarily when students independently sought out field-specific reading material. These patterns suggest that learner autonomy, when unguided, tends toward general rather than specialized vocabulary. The findings contribute to a growing body of research using platform analytics to understand vocabulary learning behavior beyond test-score outcomes alone, with implications for how such platforms might be integrated into general English courses serving students from diverse academic backgrounds and for how instructors might scaffold text selection to support field-relevant vocabulary growth.