Neural correlates of processing orthographic neighbours and predicted words during naturalistic sentence reading: A co-registered eye-tracking and MEG study

Context-based prediction is crucial for language processing, facilitating in selecting predicted words from orthographically similar candidates. However, the neural differences in processing orthographic neighbours versus predicted words in high-constraint sentence contexts remain underexplored. This study used fixation-related fields (FRF) with eye-tracking and magnetoencephalography (MEG) to capture participants’ eye movements and neural responses during naturalistic sentence reading. Experimental sentences included four conditions based on target words’ plausibility: plausible words (PC), implausible orthographic neighbours with last- (LD) or first-letter deviations (ED) from the PC target words, and unrelated words (UC). Results revealed longer first fixation durations and larger N400m FRF responses for the LD, ED, and UC than for the PC. The ED elicited larger P600m FRF responses than the LD and PC. The left inferior frontal gyrus (IFG) showed increased activity for the ED and UC than the PC during both the N400m and P600m time windows. The left temporal cortex exhibited stronger activity for the PC than the ED during the N400m time window. During the P600m time window, compared with the PC, increased right IFG activity was observed for the LD, while the right insula cortex showed greater involvement for the LD and ED. This study highlights the impact of orthographic form in sentence reading, demonstrating that even one-letter deviations significantly affect fixation-related brain responses. These findings uncover distinct neural processes for handling orthographic and semantic deviations, emphasizing the role of the left and right IFG and the right insula cortex in processing orthographic neighbours during naturalistic sentence reading.