Complex dynamics of semantic memory access in reading |
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Authors: | Giosué Baggio André Fonseca |
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Affiliation: | 1.SISSA International School for Advanced Studies, via Bonomea 265, 34136 Trieste, Italy;2.Max Planck Institute for Psycholinguistics, Wundtlaan 1, 6525 XD Nijmegen, The Netherlands;3.Center of Mathematics, Computation and Cognition, ABC Federal University, Rua Santa Adélia 166, 09210-170 Santo André, Brazil;4.The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, 34151 Trieste, Italy |
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Abstract: | Understanding a word in context relies on a cascade of perceptual and conceptual processes, starting with modality-specific input decoding, and leading to the unification of the word''s meaning into a discourse model. One critical cognitive event, turning a sensory stimulus into a meaningful linguistic sign, is the access of a semantic representation from memory. Little is known about the changes that activating a word''s meaning brings about in cortical dynamics. We recorded the electroencephalogram (EEG) while participants read sentences that could contain a contextually unexpected word, such as ‘cold’ in ‘In July it is very cold outside’. We reconstructed trajectories in phase space from single-trial EEG time series, and we applied three nonlinear measures of predictability and complexity to each side of the semantic access boundary, estimated as the onset time of the N400 effect evoked by critical words. Relative to controls, unexpected words were associated with larger prediction errors preceding the onset of the N400. Accessing the meaning of such words produced a phase transition to lower entropy states, in which cortical processing becomes more predictable and more regular. Our study sheds new light on the dynamics of information flow through interfaces between sensory and memory systems during language processing. |
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Keywords: | semantics electroencephalogram prediction error sample entropy phase transition |
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