Morphological agreement at a distance: dissociation between early and late components of the event-related brain potential.

Syntactic relationships among non-adjacent words are a core aspect of sentence structure. Research on complex sentences with displaced elements has concluded that resolving long-distance dependencies can tax working memory. Here we examine a simpler relationship-morphological agreement between the elements of a noun phrase-across a gradient of distance. Participants read sentences with violations of gender agreement among Spanish nouns, determiners and adjectives. For those explicitly assigned the task of detecting errors, accuracy was uniformly high across the four levels of distance between (dis)agreeing words. A second group performed a comprehension task as ERPs were recorded. Gender agreement errors elicited a left anterior negativity (LAN) regardless of the distance between (dis)agreeing words, indicating that the errors were detected. In contrast, a temporally later component of the ERP (P600) showed decreasing amplitudes as the number of words between (dis)agreeing elements increased. Smaller P600 responses were also associated with slower responses to the comprehension questions. Given other work suggesting that the P600 indexes attempted repair of a problematic sentence structure, the results suggest that the participants became increasingly unwilling to re-visit their initial parse of a sentence as the required effort increased, despite having noted an error. The results are discussed within the context of studies showing that readers often compute inadequate structural representations of sentences. We suggest that P600 amplitude may reflect the costs versus benefits of sentence re-analysis, determined by a combination of sentence structure, task requirements, and the degree to which sentence meaning hinges on a correct structural analysis.