Do 'early' brain responses reveal word form prediction during language comprehension? A critical review.

Current theories of language comprehension posit that readers and listeners routinely try to predict the meaning but also the visual or sound form of upcoming words. Whereas most neuroimaging studies on word prediction focus on the N400 ERP or its magnetic equivalent, various studies claim that word form prediction manifests itself in 'early', pre-N400 brain responses (e.g., ELAN, M100, P130, N1, P2, N200/PMN, N250). Modulations of these components are often taken as evidence that word form prediction impacts early sensory processes (the sensory hypothesis) or, alternatively, the initial stages of word recognition before word meaning is integrated with sentence context (the recognition hypothesis). Here, I comprehensively review studies on sentence- or discourse-level language comprehension that report such effects of prediction on early brain responses. I conclude that the reported evidence for the sensory hypothesis or word recognition hypothesis is weak and inconsistent, and highlight the urgent need for replication of previous findings. I discuss the implications and challenges to current theories of linguistic prediction and suggest avenues for future research.