Predictability, plausibility, and two late ERP positivities during written sentence comprehension

Van Petten and Luka's (2012, International Journal of Psychophysiology, 83(2), 176-190) literature survey of late positive ERP components elicited by more or less predictable words during sentence processing led them to propose two topographically and functionally distinct positivities: a parietal one associated with semantically incongruent words related to semantic reanalysis and a frontal one with unknown significance associated with congruent but lexically unpredicted words. With the goal of testing this hypothesis within a single set of experimental materials and participants, we report results from two ERP studies: Experiment 1, a post-hoc analysis of a dataset that varied on dimensions of both doze probability (predictability) and plausibility, and Experiment 2, a follow-up study in which these factors were manipulated in a controlled fashion. In both studies, we observed distinct post-N400 positivities: a more anterior one to plausible, but not anomalous, low doze probability sentence medial words, and a more posterior one to semantically anomalous sentence continuations. Taken together with an observed canonical doze-modulated N400, these dual positivities indicate a dissociation between brain processes relating to written words' sentential predictability versus plausibility, clearly an important distinction for any viable neural or psycholinguistic model of written sentence processing. (C) 2014 Elsevier Ltd. All rights reserved.