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      A Temporal Sampling Basis for Visual Processing in Developmental Dyslexia

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          Abstract

          Knowledge of oscillatory entrainment and its fundamental role in cognitive and behavioral processing has increasingly been applied to research in the field of reading and developmental dyslexia. Growing evidence indicates that oscillatory entrainment to theta frequency spoken language in the auditory domain, along with cross-frequency theta-gamma coupling, support phonological processing (i.e., cognitive encoding of linguistic knowledge gathered from speech) which is required for reading. This theory is called the temporal sampling framework (TSF) and can extend to developmental dyslexia, such that inadequate temporal sampling of speech-sounds in people with dyslexia results in poor theta oscillatory entrainment in the auditory domain, and thus a phonological processing deficit which hinders reading ability. We suggest that inadequate theta oscillations in the visual domain might account for the many magno-dorsal processing, oculomotor control and visual deficits seen in developmental dyslexia. We propose two possible models of a magno-dorsal visual correlate to the auditory TSF: (1) A direct correlate that involves “bottom-up” magnocellular oscillatory entrainment of the visual domain that occurs when magnocellular populations phase lock to theta frequency fixations during reading and (2) an inverse correlate whereby attending to text triggers “top-down” low gamma signals from higher-order visual processing areas, thereby organizing magnocellular populations to synchronize to a theta frequency to drive the temporal control of oculomotor movements and capturing of letter images at a higher frequency.

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          Dynamic predictions: oscillations and synchrony in top-down processing.

          Classical theories of sensory processing view the brain as a passive, stimulus-driven device. By contrast, more recent approaches emphasize the constructive nature of perception, viewing it as an active and highly selective process. Indeed, there is ample evidence that the processing of stimuli is controlled by top-down influences that strongly shape the intrinsic dynamics of thalamocortical networks and constantly create predictions about forthcoming sensory events. We discuss recent experiments indicating that such predictions might be embodied in the temporal structure of both stimulus-evoked and ongoing activity, and that synchronous oscillations are particularly important in this process. Coherence among subthreshold membrane potential fluctuations could be exploited to express selective functional relationships during states of expectancy or attention, and these dynamic patterns could allow the grouping and selection of distributed neuronal responses for further processing.
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            The θ-γ neural code.

            Theta and gamma frequency oscillations occur in the same brain regions and interact with each other, a process called cross-frequency coupling. Here, we review evidence for the following hypothesis: that the dual oscillations form a code for representing multiple items in an ordered way. This form of coding has been most clearly demonstrated in the hippocampus, where different spatial information is represented in different gamma subcycles of a theta cycle. Other experiments have tested the functional importance of oscillations and their coupling. These involve correlation of oscillatory properties with memory states, correlation with memory performance, and effects of disrupting oscillations on memory. Recent work suggests that this coding scheme coordinates communication between brain regions and is involved in sensory as well as memory processes. Copyright © 2013 Elsevier Inc. All rights reserved.
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              The nature of phonological processing and its causal role in the acquisition of reading skills.

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                Author and article information

                Contributors
                Journal
                Front Hum Neurosci
                Front Hum Neurosci
                Front. Hum. Neurosci.
                Frontiers in Human Neuroscience
                Frontiers Media S.A.
                1662-5161
                08 July 2020
                2020
                : 14
                : 213
                Affiliations
                [1] 1Applied Psychology and Human Factors Laboratory, School of Psychology, University of Newcastle , Newcastle, NSW, Australia
                [2] 2Visual and Cognitive Neuroscience Laboratory, Department of Optometry and Vision Sciences, University of Melbourne , Parkville, VIC, Australia
                [3] 3The Florey Institute of Neuroscience and Mental Health , Parkville, VIC, Australia
                Author notes

                Edited by: Teri Lawton, Perception Dynamics Institute (PDI), United States

                Reviewed by: Andrea Facoetti, University of Padua, Italy; John Frederick Stein, University of Oxford, United Kingdom

                *Correspondence: Kim Archer, Kimberly.Archer@ 123456uon.edu.au

                This article was submitted to Sensory Neuroscience, a section of the journal Frontiers in Human Neuroscience

                Article
                10.3389/fnhum.2020.00213
                7360833
                32733217
                d45679af-abcb-4db8-b3ba-8733e69aaea9
                Copyright © 2020 Archer, Pammer and Vidyasagar.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                History
                : 12 December 2019
                : 11 May 2020
                Page count
                Figures: 7, Tables: 2, Equations: 0, References: 285, Pages: 24, Words: 0
                Categories
                Neuroscience
                Hypothesis and Theory

                Neurosciences
                dyslexia,reading,temporal sampling,magnocellular,dorsal,theta,gamma,oscillations
                Neurosciences
                dyslexia, reading, temporal sampling, magnocellular, dorsal, theta, gamma, oscillations

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