Harry Potter and the Chamber of What?: the impact of what individuals know on word processing during reading

During reading, effects of contextual support indexed by N400 – a brain potential sensitive to semantic activation/retrieval – amplitude are presumably mediated by comprehenders’ world knowledge. Moreover, variability in knowledge may influence the contents, timing, and mechanisms of what is brought to mind during real-time sentence processing. Since it is infeasible to assess the entirety of each individual’s knowledge, we investigated a limited domain – the narrative world of Harry Potter (HP). We recorded event-related brain potentials while participants read sentences ending in words more/less contextually supported. For sentences about HP, but not about general topics, contextual N400 effects were graded according to individual participants’ HP knowledge. Our results not only confirm that context affects semantic processing by ∼250 ms or earlier, on average, but empirically demonstrate what has until now been assumed – that N400 context effects are a function of each individual’s knowledge, which here is highly correlated with their reading experience.