Eye movements and processing difficulty in object relative clauses

It is well known that sentences containing object-extracted relative clauses (e.g., The reporter that the senator attacked admitted the error) are more difficult to comprehend than sentences containing subject-extracted relative clauses (e.g., The reporter that attacked the senator admitted the error). Two major accounts of this phenomenon make different predictions about where, in the course of incremental processing of an object relative, difficulty should first appear. An account emphasizing memory processes (Gibson, 1998; Grodner & Gibson, 2005) predicts difficulty at the relative clause verb, while an account emphasizing experience-based expectations (Hale, 2001; Levy, 2008) predicts earlier difficulty, at the relative clause subject. Two eye movement experiments tested these predictions. Regressive saccades were much more likely from the subject noun phrase of an object relative than from the same noun phrase occurring within a subject relative (Experiment 1) or within a verbal complement clause (Experiment 2). This effect was further amplified when the relative pronoun that was omitted. However, reading time was also inflated on the object relative clause verb in both experiments. These results suggest that the violation of expectations and the difficulty of memory retrieval both contribute to the difficulty of object relative clauses, but that these two sources of difficulty have qualitatively distinct behavioral consequences in normal reading.