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.

This study investigates variation in article use by Korean secondary school students of English. The study shows how two different tasks affect variation with respect to article types (a, the, and zero), proficiency level and the semantic feature, specificity. One task, a wide domain task, focused on grammar in general and the narrow domain task focused on articles. The statistical results showed that the subjects performed significantly better on the narrow domain task than on the wide domain task. The subjects showed significant differences among the three articles in the wide domain task, while they did not in the narrow domain task. The subjects performed significantly better with non-specific DPs (Determiner Phrases) than with specific DPs in the wide domain task, but reversed results were revealed in the narrow domain task. The present study presents some finding that grammatical domain plays a role as a variable for variability and shows that different tasks on the same research topic may produce different findings.