1. Introduction

This chapter introduces the field of second language acquisition (SLA) and discusses the various theoretical and methodological developments that have taken place. It also presents previous reviews on SLA, highlighting the main research directions and topics explored. The limitations of previous reviews are mentioned, and the aim of the current review is outlined, which is to visualize and quantify the thematic patterns and topics of strong interest to researchers in the past decade.

2. Methodology

The present study used CiteSpace to identify research trends in a more objective and holistic manner. CiteSpace is a Java-based application used for data mining, data processing, and map generation. It generates interactive visualizations of structural and temporal patterns and trends in a scientific field. The visualization can be applied repeatedly to track the development of a field closely and extensively. Additionally, network visualizations can be generated in CiteSpace using the embedded document co-citation analysis function to identify key publications and find thematic patterns. The citation burst function can be employed to detect publications whose citation count has increased suddenly in a certain time period, which can be used to identify and predict emerging trends in the future. The study collected bibliographic records in the SLA research field from the Web of Science Core Collection of Thomson Reuters, resulting in a total of 4,660 bibliographic records.

3. Results

linguistic forms and functions by L2 learners and L1 attriters and found a universal process that first-language loss occurred well into adulthood, rather than just in early, second-language-acquisition periods. The authors also pointed out that a key symptom of language attrition was heavier reliance on lexical associations, rather than complex syntactic process.

3.2.3 Socio-cultural Perspectives

Cluster #2 is second language writing. Hyland and Hyland (2006) argued that writing should be considered a meaningful, social activity and an indispensable part of English-language education. Their research, aimed at EAP (English for academic purposes) students, provided practical suggestions for the effective promotion of L2 writing competency for students in college-level academic writing classes. Johns (2009) focused on learner training, investigating the effectiveness of using corpus in teaching L2 writing skills. The study revealed that learners could improve their awareness and knowledge of L2 vocabulary with the help of corpuses.

Cluster #5 is conversation analysis, referring to a qualitative method for studying language use in real-life contexts. Kong, Tian, and Hyland (2011) conducted a comparative study of teacher and student roles in writing conferences in English and Chinese. This was especially useful for learning L2 negotiation of meanings and teacher-student interactions in multicultural L2 classrooms. Seedhouse (2004) proposed a new method of conversation analysis, intercultural conversation analysis (ICCA), for understanding L2 talk in use, and studying this through a practical approach, using authentic conversation transcripts.

Cluster #8 is sociolinguistics. Gass and Mackey (2012) explored the use of code-switching in the classroom, focusing on the circumstances and conditions promoting the use of several linguistic codes in speech, and also the role of social competence in the process. Norton (2013) turned her attention to the key role of individual social identities and how they related to power structures in the language learning process. The author called for the cultivation of a polycentric orientation in the field of SLA, reflecting and respecting cultural and linguistic diversity in the educational context.

Cluster #11 is task-based language teaching, and Cluster #14 refers to linguistic influence, both emphasizing the dynamic relationship between language social context, learners’ target language proficiency, and situated, authentic language use and practice. Bygate (2002) maintained that language learning was a developmental process strongly associated with task-based practice. As Alptekin (2002) indicated, human experience and learning resources were better foregrounded in L2 teaching when it came to the study of borrowings and loan words.

In this section, we conducted a co-citation analysis to identify key publications in SLA research and also mapped out the main topics of research in the field during the time period of 2009 to 2019, covering psycholinguistic and neurolinguistic perspectives, linguistic perspectives, and socio-cultural perspectives.

4. Discussion and Conclusion

In the present study, the knowledge domain of SLA was visualized from 2009-2019, providing an overview based on the key publications, main clusters, and the references with high sigma values and citation bursts. The main clusters identified the research topics in recent years appealing to scholars in the field of SLA. Additionally, publications with high sigma values were of great significance in both temporal and structural development of SLA because they show that scholars’ publications can serve as a bridge between multiple research subfields. The interdisciplinary features of SLA research can be observed by integrating and referring to theoretical and practical information from other disciplines. There has been an increasing amount of research focused on the relationship between SLA and cognitive science. The future emerging trends were predicted by detecting the citation bursts, suggesting that cross-disciplinary methods in SLA research would be a potential future direction. SLA research draws its methodology and theoretical foundations from a number of other fields including linguistics, cognition, psychology, sociology, and more, showing great diversity in current approaches to SLA methodology. SLA research has shifted from being more descriptive to more explanatory. Empirical research and quantitative analysis play an increasingly important role in SLA.

The visualization of the SLA knowledge domain in 2009-2019 provides us with a clear and direct way to capture the developmental trajectory of SLA in recent years. Both the research focus and research methodology have evolved over time, and it is likely that interdisciplinary characteristics of SLA will continue to attract the attention of researchers in the foreseeable future. Nonetheless, it is important to bear in mind that SLA is a complex, non-linear, dynamic system and still in its infancy as a field of scientific inquiry. Research scopes in SLA are not yet clearly defined, and we can anticipate further shifts, developments, and setbacks in the future.