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Poster E51, Friday, November 10, 10:00 – 11:15 am, Harborview and Loch Raven Ballrooms

Time-generalized multivariate analysis of EEG activity reveals a cascading organization of semantic mismatch processing

Edvard Heikel1, Jona Sassenhagen1, Christian J. Fiebach1;1Goethe University Frankfurt

In language processing, it has been traditionally argued that the N400 and the P600 represent a double dissociation between semantic and syntactic processing. However, the P600 as a purely syntactic component has been called into question due to studies demonstrating a P600 in response to semantic violations in sentences with a high semantic constraint (i.e., high cloze probability). In light of these observations some have argued that the P600 might index a more global processing stage (Bornkessel-Schlesewsky & Schlesewsky, 2008), which implicates the additional question whether or not N400 and P600 reflect strictly sequential stages of processing. Conversely, others have argued that the observed P600 in response to semantic violations is simply a biphasic response to the N400 (Tanner et al, 2015). This is still very much debated and one reason for the lack of theoretical convergence in regards to the interpretation of semantic P600 effects could be due to the limitations of traditional univariate approaches to ERP analysis. To constrain the range of possible neural architectures represented by the biphasic N400/P600 response elicited by semantic violations – i.e., sequential vs. cascading activation of distinct processes vs. recurrent activation of a single neural mechanism – we applied a novel EEG method capable of tracking the temporal evolution of distinct cognitive processing stages over time, i.e., temporally generalized multivariate pattern decoding (generalization across time/GAT; King & Dehaene, 2014). We replicate established N400/P600 correlates of semantic mismatch in a spoken sentence paradigm, and provide evidence that early and late mismatch-sensitive processes are 1. distinct in their neural substrate, which argues against recurrent architectures, and 2. partially overlap in time, refuting strictly sequential models. Furthermore, separate multivariate pattern classifiers that were trained on N400 vs. P600 EEG patterns performed at chance outside their respective time windows (i.e., N400 vs. P600), which rules out the biphasic activation of a single system as cause of the N400/P600 pattern. These results suggest an incremental-cascading neural organization of semantic processing, i.e. a sequence of processes that are not strictly serial but overlapping in time.

Topic Area: Methods

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