Informal and Incidental Second Language Vocabulary Learning

1. Introduction

It is now widely acknowledged that the lion’s share of second language (L2) vocabulary knowledge is acquired informally or incidentally through learner-initiated exposure outside classrooms (Reynolds, 2023). Emphasizing the importance of language learner autonomy has led to the emergence of several subfields of vocabulary research, including informal digital learning of English (IDLE), extramural language learning, and incidental vocabulary acquisition, among others (see Gyllstad et al., 2025; Lee, 2019; Teng & Reynolds, 2024). The growing body of literature has enhanced our understanding of factors such as frequency and processing (e.g., Eckerth & Tavakoli, 2012); learning vocabulary from listening (e.g., Van Zeeland & Schmitt, 2013), reading (e.g., Reynolds, 2015), and writing (e.g., Brown et al., 1999); the role of multimodal input and gaming (e.g., Bisson et al., 2014; Reynolds, 2017); learner differences (e.g., Miller & Godfroid, 2020); and how incidental and intentional learning of vocabulary can complement one another (e.g., Boers, 2024). However, several pertinent issues have received limited attention. This Special Issue on informal and incidental second language vocabulary learning called for studies that would extend our understanding in a number of key areas. Among others, the Special Issue sought to explore early-years incidental L2 vocabulary learning, the relationship between early informal L2 exposure and later vocabulary size later in life, the use of generative AI in vocabulary learning, research conducted outside Western contexts, and the correlation between extramural English exposure and school-based English achievement.

2. Themes and Insights from the Special Issue

2.1. Research Context and Diversity

The extensive, yet often overlooked, body of research on L2 vocabulary acquisition originating from Iran is the focus of Paul Meara’s exploratory review [Contribution 1], “The Iranian Research on Vocabulary Acquisition: An Exploratory Review.” Meara observes that this substantial body of work, published between 2015 and 2024, remains largely unfamiliar to Western researchers because it often appears in newer or regional journals that are not indexed in standard bibliographic databases. His review seeks to map the main research concerns, prolific authors, and major intellectual influences within this growing field. The findings reveal a complex citation landscape: while a small number of Iranian authors are highly prolific, they are not always the most frequently cited, suggesting a lack of reciprocal citation within the local research community. Western scholars—particularly Nation, Schmitt, Laufer, and Meara—dominate the list of most influential figures, indicating that Iranian researchers are clearly engaged with the international field. At the same time, co-citation analyses identify clusters centered on authors such as Oxford and Gu and on themes such as vocabulary learning strategies, glossing, and subtitling, which appear more prominent than in mainstream L2 vocabulary research. These patterns suggest that Iranian research may be developing along trajectories distinct from prevailing Western trends. Overall, Meara’s analysis demonstrates that this critical mass of work is both more extensive and more compelling than has generally been recognized and deserves greater international visibility.

2.2. Early and Extramural Exposure in L2 Vocabulary Development

In “Guided Drawing with Preschool Dual Language Learners in Head Start: Building Science Vocabulary and Content Knowledge,” Christina M. Cassano and Kathleen A. Paciga [Contribution 2] report on a study investigating the effectiveness of guided drawing for enhancing vocabulary and content knowledge among preschool dual language learners (n = 13) in U.S. Head Start programs. Using a pre-test–post-test design, they examined learners’ vocabulary and conceptual understanding through an eight-session guided drawing intervention. Researcher-designed quantitative measures revealed significant gains in both vocabulary and content knowledge, while qualitative analyses of learners’ drawings identified four key themes. New knowledge was supported through guided interactions; misconceptions became visible, highlighting areas needing further instruction; and drawing-related talk revealed misunderstandings, offering insight into children’s thought processes. Cassano and Paciga conclude that guided drawing effectively supports dual language learners’ incidental acquisition of vocabulary and conceptual knowledge in meaningful contexts. The findings suggest that guided drawing can serve as a valuable instructional strategy in early childhood education.

In “Exploring the Effects of Early Extramural English Exposure on the Vocabulary Size of University Students,” Nicole Louise Busby [Contribution 5] examines how early exposure to English through extramural activities relates to second language vocabulary size in adulthood. The study involved 40 Norwegian university students who completed an online survey comprising a vocabulary size test and questions about early extramural English experiences. Participants generally perceived that their extramural engagement contributed more to their English knowledge than formal education. They recalled engaging in activities such as watching television shows, reading books, and playing digital games, with some beginning as early as age four. The participants’ vocabulary sizes ranged from 8900 to 13,800 words (M = 11,323), and time spent in early extramural English exposure associated with larger L2 vocabularies in adulthood and highlights the importance of examining early informal learning experiences as potential foundations for later language development.

Together, these two studies underscore the developmental potential of informal and incidental learning experiences from early childhood onward. Both illustrate how engagement with meaningful activities can contribute to vocabulary growth and long-term linguistic outcomes.

2.3. Out-of-School and Technology-Mediated L2 Vocabulary Learning

In “Out-of-School Exposure to English in EFL Teenage Learners: Is It Related to Academic Performance?” Linh Tran and Imma Miralpeix [Contribution 4] examine the relationship between informal exposure to English and academic performance among Spanish secondary school students (n = 2015). Using an online questionnaire covering 16 out-of-school activities, they investigated the types and frequency of students’ English exposure and their correlations with academic performance (measured by the English grade obtained in the previous academic year). The most common activity was listening to music (offline followed by online), followed by watching digital content online, reading digital materials online, and writing with digital support online, while talking face to face in English with family was least frequent. Results showed that extramural English exposure accounted for 14.2% of the variance in English grades, with positive correlations observed for speaking, reading, writing, and watching subtitled media. Interestingly, gaming showed a negative correlation with academic performance. The findings suggest that activities involving written input and output are particularly beneficial for English learning. Tran and Miralpeix recommended that educators design classroom tasks that bridge written vocabulary and listening comprehension, increase the frequency of productive language activities, and introduce learners to captioned audiovisual materials. They also emphasize the need for further research to clarify the causal relationship between out-of-school activities and proficiency outcomes.

In “Beyond the Books: Exploring Factors Shaping Chinese English Learners’ Engagement with Large Language Models for Vocabulary Learning,” Xiaochen Wang and Barry Lee Reynolds [Contribution 3] investigate factors influencing Chinese learners’ engagement with large language models (LLMs) for vocabulary learning. Drawing on self-determination theory and the unified theory of acceptance and use of technology, they surveyed 568 learners in China. Six significant factors were identified—perceived autonomy, competence, relatedness, performance expectancy, effort expectancy, and social influence—with effort expectancy emerging as the most influential predictor. Six of seven hypotheses were supported, indicating that these factors strongly predicted learners’ behavioral intentions to use LLMs. In contrast, facilitating conditions had no significant effect on motivation. These findings underscore the pedagogical potential of integrating LLMs into vocabulary instruction to create more personalized and interactive learning experiences. The authors suggest that teachers consider strategies to reduce technological barriers, promote writing and conversation simulations for active learning, and encourage the formation of peer learning communities to enhance social influence and motivation. Addressing autonomy, competence, and relatedness, they argue, can further sustain learners’ engagement and persistence in LLM-based vocabulary learning.

Together, these two studies illustrate how out-of-school and technology-mediated learning environments contribute to L2 vocabulary development. Tran and Miralpeix’s work highlights the enduring value of informal engagement with English in real-world contexts, while Wang and Reynolds’s study points to the emerging potential of AI-supported environments to expand the scope of autonomous vocabulary learning beyond the classroom.

3. Conclusions and Future Directions

This Special Issue has successfully encouraged researchers to rethink key trends and topics in the field of incidental and informal vocabulary learning. Yet, much remains to be explored. Notably, one study addressed learners’ perceptions of AI tools, but future work should move beyond perception-based research to examine, through (quasi-)experimental designs, how different LLMs and their derivative tools can be leveraged for incidental vocabulary learning. This is a particularly promising and topical area of inquiry.

It is also encouraging to see that most studies were theoretically grounded and that some incorporated qualitative data alongside quantitative analyses. However, there remains a need for more in-depth qualitative and longitudinal investigations, especially in early childhood contexts where data collection can be challenging. Such approaches would provide richer insights into the processes underlying incidental learning over time.

A further observation concerns the narrow focus on English as the target language. Future studies should broaden the scope to include other target languages and productive learning tasks that involve oral communication and interaction. Moreover, given that reading increasingly occurs in multimodal environments, researchers should also examine how textual, visual, and auditory modes jointly contribute to or hinder incidental learning.

While these remaining gaps could be viewed as limitations to this Special Issue, they also represent opportunities. The field is ripe for innovation and growth. I encourage the next generation of researchers to take up these challenges and pursue ambitious studies that deepen our understanding of incidental vocabulary learning in diverse, real-world contexts.