Agreement Errors Disrupt Eye Movements in Reading Only When They Are Detected

Sentence processing models posit that syntactic processing difficulty contributes to the processing time of each word (e.g., Lewis & Vasishth, 2005). On the other hand, the E-Z Reader 10 model of eye movements in reading (Reichle et al., 2009) proposes that syntactic processing affects eye movements only when integration of an input word fails. We present two eye movement experiments designed to address this tension. Readers were presented with ungrammatical sentences with a singular subject and a plural verb, but with a plural local noun that often induces an illusion of grammaticality, e.g., *The editor of the magazines are reviewing the articles before publication. After each critical sentence was removed from the screen, the reader made a binary acceptability judgment. When readers rejected the ungrammatical critical sentences, there was also pronounced disruption to incremental reading. However, on the majority of trials readers accepted these sentences, and on those trials the eye movement record revealed only a very small increase in reading time compared to corresponding grammatical sentences; critically, this small effect was entirely explained by the difference between conditions in the lexical surprisal of the verb. Thus, as predicted by E-Z Reader 10, an effect of agreement computation above and beyond the effect of surprisal was in evidence only when agreement computation failed, i.e., the sentence was rejected. We discuss implications for models of incremental sentence processing and reading.