Multiple dependencies and the role of the grammar in real-time comprehension

Wh-dependencies are known to be formed rapidly in real-time comprehension. The parser posits the location of gap sites in advance of the bottom-up evidence for missing constituents, and must therefore have a means of deciding when and where to project dependencies. Previous studies have observed that the parser avoids building ungrammatical wh-dependencies, for example, by restricting the search for gap sites from island domains. This paper tests the stronger claim that constraints are not merely respected, but that grammatical knowledge actively prompts the construction of some representations in advance of the input. Three self-paced reading experiments examined patterns of wh-dependency formation in multiple-dependency constructions: obligatory across-the-board (ATB) extraction from coordinated verb phrases, and from optional parasitic gaps in post-verbal adjunct clauses. The key finding is that comprehenders immediately enforce the requirement for extraction from coordinates, and hence actively search for multiple gap sites within a coordinate VP; but they do not search for post-verbal parasitic gaps. This difference cannot be attributed to relative differences in acceptability, as comprehenders rated both of these multiple-gap constructions equally highly, nor can it be explained by general parsing incentives to develop maximal incremental interpretations of partial strings. More plausibly, the difference reflects the deployment of detailed grammatical knowledge in a parser that is motivated to satisfy structural licensing requirements in real time.