The Interface Hypothesis (Sorace, 2011; Sorace & Filiaci, 2006; Sorace & Serratrice, 2009; Tsimpli & Sorace, 2006, among others) states that the grammar external interface is more vulnerable for advanced L2ers or bilinguals than the grammar internal interface, and L1 discourse influence is one factor responsible for their residual difficulty (Sorace, 2005; Sorace, Serratrice, Filiaci & Baldo, 2009). Their study, however, did not disentangle interface effects from L1 influence and it is unclear whether the residual difficulty of advanced L2ers is due to interface effects or L1 influence. The results of the present study which teases the two factors apart show that L1 influence is stronger than interface effects. The results without L1 influence show that the syntax-discourse interface is more vulnerable than the syntax-morphology interface, supporting the Interface Hypothesis. This study examines two sets of data, cross-sectional and longitudinal, on overpassivization of L2 English unaccusative verbs by Chinese and Korean speakers.

1. INTRODUCTION
 2. THE INTERFACE HYPOTHESIS AND L2 ENGLISH UNACCUSATIVES
  2.1. The Interface Hypothesis
  2.2. L2 English Unaccusatives
  2.3. Research Questions
 3. STUDY ONE: CROSS-SECTIONAL STUDY
  3.1. Method
  3.2. Results
 4. STUDY TWO: LONGITUDINAL STUDY
  4.1. Method
  4.2. Results
 5. DISCUSSION
  5.1. The Syntax-Discourse Interface and the Syntax-Morphology Interface
  5.2. Other Issues in the Interface Hypothesis
 6. CONCLUSION
 REFERENCES

• Taegoo Chung(Korea University)