From Exposure to Understanding: How Cognitive and Linguistic Factors Shape L2 Vocabulary Learning in Digital Environments

Abstract

This thesis investigates the cognitive and linguistic factors that influence second-language (L2) vocabulary and morphological learning in app-based digital environments. Across three studies, I examine how exposure type, morphological structure, semantic transparency, and learners’ L1 backgrounds shape English vocabulary acquisition and morphological abstraction. The first study focused on incidental L2 vocabulary learning within a cloze-translation task, distinguishing between target encounters (when a word is explicitly practiced) and context encounters (when it appears indirectly). Results indicated that context encounters facilitated learning even during initial target exposures, though gains from incidental learning were smaller than those from explicit practice, highlighting the role of cognitive load and task difficulty in vocabulary acquisition. The second study investigated how L2 learners acquire morphological knowledge through app-based vocabulary training, examining the roles of repetition (token frequency), variability (type frequency), and semantic transparency. Successful morphological learning depended on repeated exposure to suffixes, particularly when they appeared in diverse lexical contexts, while non-morphemic sequences conferred no advantage. Type frequency emerged as a strong predictor of learning, and L1 background modulated performance: German-speaking learners, whose L1 shares morphological and typological similarities with English, showed substantial gains, whereas Japanese-speaking learners showed minimal improvement. The third study examined compound word learning, evaluating transparency at the whole-word and constituent (modifier and head) levels. Whole-word and head transparency consistently facilitated learning across language groups, while cross-linguistic differences emerged in sensitivity to modifier transparency, suggesting an interaction between universal semantic constraints and L1-specific processing strategies. Together, these studies demonstrate that L2 vocabulary and morphological learning are experience-driven, meaning-sensitive, and shaped by linguistic background. The findings advance theoretical models of lexical processing and provide evidence-based guidance for the design of adaptive, effective digital language-learning tools.