With a growing interest in heritage languages from researchers of bilingualism and linguistic theory, the field of heritage-language studies has begun to build on its empirical foundations, moving toward a deeper understanding of the nature of language competence under unbalanced bilingualism. In furtherance of this trend, the current work synthesizes pertinent empirical observations and theoretical claims about vulnerable and robust areas of heritage language competence into early steps toward a model of heritage-language grammar. We highlight two key triggers for deviation from the relevant baseline: the quantity and quality of the input from which the heritage grammar is acquired, and the economy of online resources when operating in a less dominant language. In response to these triggers, we identify three outcomes of deviation in the heritage grammar: an avoidance of ambiguity, a resistance to irregularity, and a shrinking of structure. While we are still a ways away from a level of understanding that allows us to predict those aspects of heritage grammar that will be robust and those that will deviate from the relevant baselines, our hope is that the current work will spur the continued development of a predictive model of heritage language competence.

Our keynote, “Understanding heritage languages” (Polinsky & Scontras, 2019), and the commentaries to it make the following main points.

Many human infants grow up learning more than one language simultaneously but only recently has research started to study early language acquisition in this population more systematically. The paper gives an overview on findings on early language acquisition in bilingual infants during the first two years of life and compares these findings to current knowledge on early language acquisition in monolingual infants. Given the state of the research, the overview focuses on research on phonological and early lexical development in the first two years of life. We will show that the developmental trajectory of early language acquisition in these areas is very similar in mono- and bilingual infants suggesting that these early steps into language are guided by mechanisms that are rather robust against the differences in the conditions of language exposure that mono- and bilingual infants typically experience.

For close to a century, experiments using artificial languages (hereafter ALs) have been a staple of psycholinguistic research (Esper, 1925). Contemporary AL research has spanned numerous levels of linguistic inquiry, from phonetic learning through syntax (see Culbertson & Schuler, 2019). This approach has also been successfully applied across development, from infants and children (see Saffran & Kirkham, 2018) through older adults (e.g., Schwab, Schuler, Stillman, Newport, Howard & Howard, 2016), even spanning cross-species comparisons (e.g., Wilson, Slater, Kikuchi, Milne, Marslen-Wilson, Smith & Petkov, 2013). Given the proliferation of AL methods for investigating issues related to first language acquisition, it is not surprising that research on bilingualism has also embraced this approach. This special themed section comprises four concise review articles describing how AL research has informed questions related to bilingualism and second language learning. The articles also discuss the strengths and limitations of this approach, as well as pointing to future directions for the field.