Feature typology and L2 proficiency matter: L3 acquisition of Portuguese

To determine the source of transfer in third language acquisition (L3A), we tested the effects of grammatical feature typology and L2 Spanish proficiency on the comprehension and production of grammatical [gender] and [number] in the early stages of L3A of Portuguese. We distinguish between the two features based on their participation in the lexical-conceptual structure of the lemma and its interaction with the morpho-syntactic derivation. L1 English speakers were tested on their knowledge of the features in both their L2 and their L3 through a grammaticality judgment task and an elicited production task. Results show that L3 learners transfer only some features, specifically [gender] rather than [number], suggesting a fine-grained divide in feature compositionality between the structural ([gender]) and semantic ([number]) features. We also found facilitative transfer only after a threshold acquisition in L2, in support of the Threshold Hypothesis. For beneficial transfer of a feature, mere knowledge of the L2 structure was found to be sufficient. However, a higher generalized L2 proficiency threshold was found to predict high L3 accuracy.