Off-line sentence processing: what is involved in answering a comprehension probe?

The aim of this study was to better characterize the influence of the comprehension probe on syntax-related activation patterns observed in fMRI studies of sentence comprehension. In this study, sentence comprehension was assessed by presenting a true/false statement after each sentence. To disassociate the sentence reading from the comprehension probe activation, a 6-s delay was placed between these processing phases. Two factors were manipulated, one affected the sentence and the other affected the probe. The sentences were manipulated by varying their syntactic complexity; conjoined-active and object-relative sentences were examined. The comprehension probes asked whether one of the first two mentioned nouns in the preceding sentence performed the action of one of the two verbs. The probes were manipulated by varying the distance (number of intervening words) between the noun and verb within the sentence; there were three probe types: short distance, long distance, and false statements. The results, which focused on the processing taking place during the probe, showed that the distance manipulation resulted in significant differences in both behavioral and brain activation measures. This was particularly true of BA 44, which revealed an interaction between complexity and distance such that the complexity effect was all but eliminated for the long-distance condition. Additionally, we replicated our previous finding of syntactic complexity effects during the probe phase. Finally, post hoc analysis revealed that participants used two distinct strategies during sentence reading; significant effects of strategy use on both behavioral and brain activation data were observed.