This study addresses the following questions: (1) What kind of unique phonological characteristics do heritage Japanese learners share? (2) Does L1 or L2 Japanese share these characteristics? (3) Do these characteristics correspond in oral and written production? (4) What could affect phonological transfer? Longitudinal/cross-sectional data to identify phonological transfer from English to heritage Japanese were collected from diary entries/compositions as well as oral and written tests by heritage Japanese learners growing up in Australia, compositions and written tests by Japanese monolinguals in Japan, and essay translations by L1 English speakers learning Japanese as an L2 in Australia. Possible phonological transfer features in heritage Japanese were examined to see if they occur in the L1 and L2. Correspondences between oral and written transfer features were also investigated, and quantitative analyses examined factors associated with phonological transfer. Findings indicate that phonological transfer is acquisitional, possibly influenced by literacy, the mental lexicon, and both sociocultural and individual factors.

For bilinguals, the use and knowledge of one language affects how they process the other. Various cross-linguistic influences (CLI) can be observed in both language production and comprehension across all domains of linguistics. We start by broadly exploring the concept of transfer, both negative and positive, and forward and reverse. In doing so, we identify various classifications of CLI. Following this, we review key studies on phonological, lexical, morphological, and syntactic transfer along with other types such as discursive, pragmatic, and sociolinguistic. We find that there are a number of factors that can determine the degree to which transfer emerges or whether it happens at all. We then review studies investigating the ability to switch between the two language systems. In doing so, we look at theoretical models that explain what facilitates language switching and what empirical studies tell us about the neural and electrophysiological activity that arises in language switching. Finally, we discuss dreaming and bilingualism and argue that dreaming in an L2, contrary to popular belief, does not necessarily imply fluency in that language.