Why Second Language Acquisition of sign languages matters to general SLA research

SLA research is characterised by a striking homogeneity in the linguistic, social and geographical data we as a field draw on. Such empirical homogeneity is a potential threat to the validity and scope of our models and theories. This paper focuses on a particular gap in our knowledge, namely the SLA of sign languages. It outlines an argument as to why the SLA of sign matters to general SLA research in terms of the empirical representativity, generalisability, and validity of the conclusions in the field. It exemplifies three domains where the study of language acquisition across modalities could shed important light on theoretical issues in mainstream SLA/bilingualism research (e.g. learner varieties, explicit-implicit learning, and crosslinguistic influence), and highlight some of the methodological challenges involved in such work.