Why are multiword units hard to acquire for late L2 learners? Insights from cognitive science on adult learning, processing, and retrieval

Multiword units have experienced renewed interest in recent research due to their prominent role in usage-based approaches to general linguistics, as well as in work on bilingualism and second language acquisition. While work in the last few decades focused on figurative multiword units (i.e., idioms), a growing number of studies have more recently focused on non-figurative units (collocations in particular, but also binomials or lexical bundles, for example). This work has highlighted not only the relevance of multiword units in language, but also the particular challenges that arise for non-native speakers acquiring conventional units in a second language. Despite important findings across linguistics, psycholinguistics and psychology, the sources of L2 difficulties have not been adequately and systematically investigated. The present paper brings together insights from different strands of the literature to review difficulties at three distinct loci, namely, input exposure, processing and retrieval.