The contribution of fronto-parietal regions to sentence comprehension: insights from the Moses illusion

To interpret a sentence, the reader must not only process the linguistic input, but many times has also to draw inferences about what is implicitly stated. In some cases, the generation and integration of inferred information may lead to semantic illusions. In these sentences, subjects fail to detect errors such as in "It was two animals of each kind that Moses took on the ark" despite knowing that the correct answer is Noah, not Moses. The relative inability to notice these errors raises questions about how people establish and integrate inferences and which conditions improve error detection. To unravel the neural processes underlying inference and error detection in language comprehension, we carried out an fMRI study in which participants read sentences containing true or false statements. The false statements either took the form of more obvious (i.e., clearly false) or subtle (i.e., semantic illusions) inconsistent relations. Participants had to decide if each statement was true or false. Processing semantic illusions relative to true and clearly false sentences significantly engaged the right inferior parietal lobule, suggesting higher demands in establishing coherence. Successful versus unsuccessful error detection revealed a network of regions, including right dorsolateral prefrontal cortex, orbitofrontal, insula/putamen and anterior cingulate cortex. Such activation was significantly correlated with overall response accuracy to the illusions. These results suggest that to detect the semantic conflict, people must inhibit the tendency to draw pragmatic inferences. These findings demonstrate that fronto-parietal areas are involved in inference and inhibition processes necessary for establishing semantic coherence.