The Relation between Alpha/Beta Oscillations and the Encoding of Sentence induced Contextual Information

Jan-Mathijs Schoffelen,René Terporten,Bohan Dai,Peter Hagoort,Anne Kösem

doi:10.1038/s41598-019-56600-x

Abstract

Pre-stimulus alpha (8–12 Hz) and beta (16–20 Hz) oscillations have been frequently linked to the prediction of upcoming sensory input. Do these frequency bands serve as a neural marker of linguistic prediction as well? We hypothesized that if pre-stimulus alpha and beta oscillations index language predictions, their power should monotonically relate to the degree of predictability of incoming words based on past context. We expected that the more predictable the last word of a sentence, the stronger the alpha and beta power modulation. To test this, we measured neural responses with magnetoencephalography of healthy individuals during exposure to a set of linguistically matched sentences featuring three levels of sentence context constraint (high, medium and low constraint). We observed fluctuations in alpha and beta power before last word onset, and modulations in M400 amplitude after last word onset. The M400 amplitude was monotonically related to the degree of context constraint, with a high constraining context resulting in the strongest amplitude decrease. In contrast, pre-stimulus alpha and beta power decreased more strongly for intermediate constraints, followed by high and low constraints. Therefore, unlike the M400, pre-stimulus alpha and beta dynamics were not indexing the degree of word predictability from sentence context.

Highlights

Sentence level language comprehension results from dynamic cognitive processes which combine and unify smaller linguistic units to create meaning[1,2,3,4,5,6]
In order to confirm the participant’s attention to the experimental task, their performance was measured during catch trials that occurred after presentation of 20% of the sentences
The cluster-based statistics revealed a main effect of context constraints on the M400 amplitude strength in a pre-defined time window of 250 ms to 600 ms after target word onset; this effect was most pronounced over a left-frontal localized cluster of sensors (Fig. 2, cluster p = 0.005)

Summary

Introduction

Sentence level language comprehension results from dynamic cognitive processes which combine and unify smaller linguistic units to create meaning[1,2,3,4,5,6]. These cognitive processes occur online, while the sentence unfolds, instantiating unified meaning which relates to the computation of semantics, spanning the whole utterance. While not being linked to predictive processes directly, these N400 modulations suggests that sentence context constraints alter predictions that are encoded prior to target word occurrence. Theta and gamma oscillatory activity has mostly been observed as neural markers for semantic predictions after target word presentation. LC (EN) In this area you got a good view

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Results

Conclusion