Early and late learners decompose inflected nouns, but can they tell which ones are inflected correctly?

An auditory lexical decision task tests morphological decomposition and sensitivity to violations in inflection in late second language learners, early learners (heritage speakers), and native speakers of Russian. Two datasets compared reaction times and error rates to real Russian inflected nouns and nonce nouns. Two parameters of real nouns were manipulated: case (the nominative, or the oblique case), and inflection (overt or zero). Nonce nouns had (a) real stems and inflections combined in an illegal way ( lemoning ), and (b) inflected nonce stems ( lemosing) . Results suggest that heritage and late learners process inflectional morphology; however, their processing of inflected words is unreliable: they are willing to accept words with incongruent inflections. While no major differences were found in the processing patterns of early and late learners, a developmental trajectory was observed in both groups of learners: their sensitivity to violations in inflection improved with proficiency.