LAUSR

The Interface Hypothesis (IH) postulates that interface structures are potentially vulnerable to incomplete acquisition in the end-state L2. Two plausible explanations have been suggested as possible causes of the L2 divergence at the interface: (1) the interaction between two competing grammatical systems, and (2) differences between monolinguals and bilinguals in integrating information from different domains in L2. This study aims to contribute to a deeper understanding of the interface phenomenon and to examine the extent to which L1 interference might account for L2 divergence at the interface. To this end, the study examines the use of Turkish accusative case (AC) in the end-state L2 grammar of L1 Russian and L1 English advanced users of L2 Turkish. The findings provide additional evidence for the IH and suggest that L2 divergence at the interface is likely to reflect more differences between monolinguals and bilinguals in integrating information from different domains rather than L1 interference.