During the temporal delay between the filler and gap sites in long-distance dependencies, the "active filler" strategy can be implemented in two ways: the filler phrase can be actively maintained in working memory ("maintenance account"), or it can be retrieved only when the parser posits a gap ("retrieval account"). The current study tested whether filler content is maintained during the processing of dependencies. Using a self-paced reading paradigm, we compared reading times on a noun phrase (NP) between the filler and gap sites in object relative clauses, to reading times on an NP between the antecedent and ellipsis sites in ellipsis sentences. While in the former type of dependency a filler by hypothesis can be maintained, in the latter there is no indication for the existence of a dependency prior to the ellipsis site, and hence no maintenance. By varying the amount of similarity-based interference between the antecedent and integration sites, we tested the influence of holding an unresolved dependency on reading times. Significantly increased reading times due to interference were found only in the object relative condition, and not in the ellipsis condition, demonstrating filler maintenance costs. The fact that these costs were measured as an effect on similarity-based interference indicates that the maintained representation of the filler must include at least some of the features shared by the interfering NP.
Keywords: Filler-gap dependencies; Long-distance dependencies; Parsing; Sentence processing; Syntax; Working memory.