Context modulates neural activity of N400 and P600 to visual words

• We used ERPs to investigate the context effect between the phrase and sentence tasks.
• Sentence task has better behavioral performance compared to the phrase task.
• Contextual modulation results in larger parietal phrasal-N400 and sentential-P600.
• Context modulates the inverse asymmetry of N400 activity in both tasks.
• Fusiform gyrus and parahippocampal gyrus involve in the local contextual processing.

An ERP experiment was conducted to investigate the contextual modulation of neural activity of N400 and P600 to visual words in Chinese phrases and sentences tasks. The materials of the phrase task (e.g., i.e., a (zhang: classifying thin and complanate things) + sheet/heart/insist) were contained in the sentence task to constitute the local context of the sentence task, and the subjects (e.g., i.e., mother) and predicates (e.g., , i.e., sets) constituted the global context of the sentence task. Behavioral performance was better for the sentence task than for the phrase task. Contextual modulation resulted in larger parietal N400 in the phrase task and a larger parietal P600 in the sentence task. N400 amplitudes were larger in the left than right hemisphere in the phrase task, whereas an inverse trend in the sentence task. Syntactic violation can evoke an N400 effect in the sentence task due to a longer semantic context relative to the phrase task. The P600 may represent later semantic and syntactic integration rather than pure syntactic processing. The results of standard low-resolution electromagnetic tomography method (sLORETA) showed that the possible generators for the significant N400 and P600 were distinct but overlapping parts of the frontal, temporal and parietal lobes. Two areas, fusiform gyrus and parahippocampal gyrus, appeared to be specifically involved in the local contextual processing. The sentence task elicited greater semantic conflict effect at left inferior frontal gyrus than that of the phrase task, additionally, there were more robust activation at right inferior parietal lobule and left superior temporal gyrus for the syntactic conflict effect of the sentence task than that of the phrase task. Above results suggest that the semantic context can facilitate the comprehension and performance of tasks, and Chinese phrase and sentence processing were relevant to common and differential neural mechanisms.