Key issues concern language development, use, perception, processing and loss in both early multilingual children and adult language learners. The focus is on all linguistic levels – phonetic and phonological, morphological and lexical, syntactic, semantic and pragmatic – as well as on both spoken, written, and signed language.
Common questions concern universal features of learner language, influences from other languages (especially the first language), how communicative and interactional skills develop over time, and effects of individual differences in learning age, language aptitude, motivation, and memory capacity. The research is partly anchored in the research field Second Language Acquisition (SLA), which in turn draws theoretical and methodological inspiration from, e.g., general linguistics, psycho- and neurolinguistics, psychology, cognitive science, and classroom-oriented learning research.
Experimental methods are often used, where data comes from language testing or brain imaging, but there are also longitudinal case studies, as well as corpus-based research, where data consists of learners' spontaneous or elicited language production.