Understanding the Constraints on Syntactic Generation: Lexical Bias and Discourse Congruency Effects on Eye Movements

We measured eye movements as people read short stories. The target sentences contained noun/verb homographs (e.g. “duck”) and were preceded by a biasing context sentence. The homograph in the target sentence was always disambiguated by a case-marked pronoun: e.g., “She saw his/him duck.” Lexical bias effects (reflecting the relative frequency of the noun and verb forms) were found in the initial fixations on the homograph. In contrast, discourse congruency effects were first observed several words downstream in the probability of a regressive eye movement. Strong discourse congruency effects were also observed in the second pass reading times. We concluded that the lexical bias effects reflect processing difficulty during the initial generation of syntactic structure, while the discourse congruency effects reflect later anomaly detection. Thus, the data challenge syntactic processing models in which all relevant and available constraints are brought to bear uniformly and simultaneously.