ERP effects of the processing of syntactic long-distance dependencies

In behavioral studies on sentence comprehension, much evidence indicates that shorter dependencies are preferred over longer dependencies, and that longer dependencies incur a greater processing cost. However, it remains uncertain which of the various steps involved in the processing of long-distance dependencies is responsible for the increased cost of longer dependencies. Previous sentence comprehension studies using event-related potentials (ERPs) have revealed response components that reflect the construction [J. King, M. Kutas, Who did what and when? Using word- and clause-level ERPs to monitor working memory usage in reading. Journal of Cognitive Neuroscience, 7, (1995) 376-395.] and completion [E. Kaan, A. Harris, E. Gibson, P. Holcomb, The P600 as an index of syntactic integration difficulty. Language and Cognitive Processes, 5, (2000) 159-201.] of long-distance wh-dependencies. This article reports one off-line rating study and one ERP study that manipulated both the presence of wh-dependencies and the length of the dependencies (one clause vs. two clauses), with the aim of clarifying the locus of length-sensitivity and the functional role of associated ERP components. Results of the off-line study confirm that longer wh-dependencies incur greater processing cost. Results of the ERP study indicate that both a sustained anterior negativity that follows the initiation of the wh-dependency and also a late posterior positivity (P600) that marks the completion of the dependency are sensitive to the presence of a wh-dependency, but do not show amplitude variations reflecting the length of the dependency. However, the P600 is delayed when it marks the completion of a longer wh-dependency. This suggests that both the sustained negativity and the P600 reflect length-insensitive aspects of the construction of syntactic dependencies. In addition, an N400 component is elicited in the middle of the two clause wh-dependency, upon encountering a verb with an argument structure that prevents completion of the dependency.