Poster C28, Friday, August 17, 10:30 am – 12:15 pm, Room 2000AB
The relation between alpha/beta oscillations and the encoding of sentence induced contextual information
René Terporten1,2, Anne Kösem2, Bohan Dai1,2, Jan-Mathijs Schoffelen2, Peter Hagoort1,2;1Max Planck Institute for Psycholinguistics, 2Donders Centre for Cognitive Neuroimaging
A sentence's context dynamically and flexibly constraints the way semantics are inferred by a reader. This process is suggested to engage brain mechanisms that flexibly predict upcoming input based on the amount of information provided by past sentential context. Here, we put this to the test by focusing on the functional role of neuronal oscillations as marker for the effects of sentence context constraints onto brain dynamics. In this magnetoencephalography study, participants carefully read a word-by-word presentation of sentences. These sentences belonged to linguistically matched lists of three levels of context constraints (high, medium and low context constraints), defined by the sentences' cloze probability. Oscillatory dynamics in the alpha/low-beta frequency band were investigated prior and after the display of a sentence's target word; amplitude modulations of the N400 component were obtained after target word onset. We predicted that the induced predictability of the target word by the different context constraints would gradually influence the amplitude of the N400 component. If alpha/low-beta power marks the buildup of contextual predictions, we hypothesized that it should monotonically relate to the levels of constraints and would therefore fit within a functional prediction account. Alternatively, alpha/beta oscillations could reflect the engagement of cognitive control operations during language processing. Such operations would not necessarily lead to the assumption of a monotonous relationship between alpha/beta power and context constraints. The results indicated that the N400 amplitude was monotonically related to the degree of context constraint, with a high constraining context resulting in the strongest amplitude decrease. On the contrary, alpha and beta power were non-monotonically related to context constraints. The power decrease was strongest for intermediate constraints, followed by high and low constraints prior to target word onset. These effects were source-localized to a set of parietal cortical areas. While the monotonous N400 modulation fits within a framework of prediction, the non-monotonous oscillatory results are not easily reconciled with this idea. Instead, it is suggested that the alpha and beta power modulations as well as their topography reflect the different demands put onto a domain general control machinery during sentence context encoding.
Topic Area: Meaning: Lexical Semantics