Parafoveal and foveal N400 effects in natural sentence reading: A timeline of semantic processing from fixation-related potentials

Abstract

The depth at which parafoveal words are processed during reading is an ongoing topic of debate. Recent studies using RSVP-with-flanker paradigms have shown that implausible words within sentences elicit N400 components while they are still in parafoveal vision, suggesting that the semantics of parafoveal words can be accessed to rapidly update the sentence representation. To study this effect in natural reading, we combined the co-registration of eye movements and EEG with the deconvolution modeling of fixation-related potentials (FRPs) to test whether semantic plausibility is processed parafoveally during Chinese sentence reading. For one target word per sentence, both its parafoveal and foveal plausibility were orthogonally manipulated using the boundary paradigm. Consistent with previous eye movement studies, we observed a delayed effect of parafoveal plausibility on fixation durations that only emerged on the foveal word. Crucially, in FRPs aligned to the pre-target fixation, a clear N400 effect emerged already based on parafoveal plausibility, with more negative voltages for implausible previews. Once participants fixated the target, we again observed an N400 effect of foveal plausibility. Interestingly, this foveal N400 was absent whenever the preview had been implausible, indicating that when a words (im)plausibility is already processed in parafoveal vision, this information is not revised anymore upon direct fixation. Implausible words also elicited a late positive complex (LPC), but exclusively in foveal vision. Our results provide convergent neural and behavioral evidence for the parafoveal uptake of semantic information, but also indicate different contributions of parafoveal versus foveal information towards higher-level sentence processing.