Processing multiple gap dependencies: Forewarned is forearmed

- Multiple gap dependencies reveal the source and scope of active processing.
- Parallelism guides active processing in coordinate extraction structures.
- The parser uses parallelism to generate fine-grained syntactic predictions.
- Parallelism in coordinate extraction structures reflects a grammatical constraint.

Many studies have shown that when forming a filler-gap dependency, comprehenders attempt to posit a gap site in advance of the input. However, it remains an open question what information they use to determine gap locations. The current study investigates parallelism in coordinate extraction structures, and asks whether comprehenders use parallelism constraints to structure their expectations about upcoming gap sites. Using a filled-gap paradigm, Experiments 1 and 2 show that comprehenders rely on parallelism to restrict the search for upcoming gap sites to specific locations in sentences with coordinate extraction. Experiment 3 shows that this effect cannot be reduced to processing factors, but may be due to a grammatically-based constraint on parallel extraction. Together, these results shed new light on the source and scope of active processing and parallelism effects in comprehension.