Abstract

Bilingual subtitles can help second language learners understand audiovisual materials (Dizon & Thanyawatpokin, 2021). However, learners may pay insufficient attention to unfamiliar L2 word forms when viewing videos with bilingual subtitles (Wang & Pellicer-Sánchez, 2022). Textual enhancement, such as highlighting target words and their translations, may draw learners’ attention to vocabulary and support vocabulary learning (e.g., Baleghizadeh & Mohajer, 2025; Li et al., 2026). The current study investigated the effects of textually enhanced bilingual subtitles on students’ incidental learning of English vocabulary at a Japanese university.

Participants were randomly assigned to either a standard bilingual subtitle group or a textually enhanced bilingual subtitle group, in which the English target words and their Japanese translations were highlighted. They first completed the updated Vocabulary Levels Test (uVLT) to assess their general vocabulary knowledge and a vocabulary pretest (i.e., meaning recall) to measure their prior knowledge of the 36 target items. After watching the video, they completed an immediate posttest measuring form recognition, meaning recognition, and meaning recall. A delayed posttest was administered approximately two weeks later to examine vocabulary retention. Video comprehension was also assessed immediately after viewing. Two questionnaires examined participants’ perceptions of the subtitles and their learning experience.

Vocabulary test responses are analyzed using GLMMs. The study also examines whether the frequency of target-word occurrence affects vocabulary learning. Video comprehension scores are compared between the two subtitle conditions. It is hypothesized that textual enhancement will promote vocabulary learning by making the connections between English word forms and their Japanese meanings more noticeable. However, it is also hypothesized that textually enhanced bilingual subtitles will hinder viewers’ comprehension of the video content by placing additional demands on their attention. The findings will provide practical implications for the design and use of bilingual subtitles in second language learning.