Evidence for automatic sentence priming in the fusiform semantic area: convergent ERP and fMRI findings

Event-related potential (ERP) studies of semantic processing have generally focused on the N400, a component that peaks at about 400 ms in response to words and which is larger when words are incongruent with the preceding sentence context. An earlier left-lateralized posterior N2(p3) has also been found to be correlated with an "unexpectedness" rating for incongruent sentence endings [Dien, Frishkoff, Cerbone, and Tucker, 2003, Parametric analysis of event-related potentials in semantic comprehension: evidence for parallel brain mechanisms, Cognitive Brain Research, 15: 137-153]. Because the incongruent endings were too odd to be explicitly predicted, we here hypothesize that this rating, and hence the N2(p3), reflects the degree of automatic spreading activation (ASA) in the visual lexical network rather than semantic expectancy, an interpretation also consistent with the early latency of this ERP (208 ms). In order to identify the brain systems involved in these linguistic processes, functional magnetic resonance imaging (fMRI) was utilized in a replication of the ERP study [Dien, Frishkoff, Cerbone, and Tucker, 2003, Parametric analysis of event-related potentials in semantic comprehension: evidence for parallel brain mechanisms, Cognitive Brain Research, 15: 137-153]. We found that activation in the fusiform semantic area (FSA), an area that converges with the source solution for the N2(p3), responded to the "unexpectedness" parameter in the same manner as the N2(p3) component. These findings suggest that the FSA helps mediate ASA processes and that the N2(p3) can serve as an index of ASA. Furthermore, close effects were found in the superior frontal gyrus and the inferior frontal gyrus that could reflect subvocalization and semantic selection processes respectively.