Dependency formation interacts with case: Evidence from Korean double nominative constructions

The subject-object asymmetry in relative clauses, where structures containing subject dependencies are typically easier to process than those with object dependencies, has been previously attributed to both grammatical function (subject > object) as well as morphological case (e.g., nom > acc). We investigate processing of Double Nominative Constructions (“DNCs”) in Korean, where the object exceptionally has nominative case like the subject (i.e., nom-nom).  This enables isolation of grammatical function and case as possible factors driving the so-called “subject advantage.” We find that dependency formation is more costly in DNCs as compared with nom-acc structures, especially for object relative clauses. We tie this effect to distinctness in morphological case of the subject and object, suggesting that the less morphosyntactically distinct the subject and object are, the more difficult it is to process DNCs in dependencies.