In this chapter, we consider different definitions of bilingualism, underscoring the reality that there are various aspects which should be taken into account when investigating bilingualism, particularly when designing studies and choosing participants. Bilingualism is a complex construct and should be viewed on a continuum. Crucially, many key details about bilinguals’ backgrounds need to be reported in studies to make results comparable and clearly linkable to the specific study sample. Relative proficiency level seems to be the most influential factor, but it is by no means the only factor relevant for studying bilingualism. Rather, individual differences and their variability, dynamically related dimensions and their interaction over time, speech environment and their changes, language use habits, socioeconomic background, and so on have been reported to influence language processing and even brain function to some extent.

This chapter discusses noticing of corrective feedback (CF) and factors that affect noticing in different contexts in previous studies. Laboratory studies found that the type of error, the length and salience of the CF, the proficiency level of the learner, and their working memory capacity, attention control, and analytical ability affected noticeability of CF. In classroom studies, the explicitness of the CF and learners' anxiety in language classrooms additionally influenced their noticing of CF. A further finding of studies is that there are discrepancies between teachers' intentions in giving CF and learners' interpretations of that CF. In peer work, the relationship between learners were closely related to the noticng of CF. Computer-based text chats have certain strengths in terms of contributing to learners' noticing of CF, such as the slow pace of the communication and the re-readibility of the text messages. However, delayed CF, and less social and affective engagement due to characteristics of text chats seemed to contribute to less noticeability of CF. In future studies, it will be necessary to examine how and when noticing leads to understanding to explore the process of deeper learning.