| Sumario: | There is growing evidence from studies of neuronal oscillations that the brain “samples” sensory information at multiple temporal levels, with important consequences for some of the long-standing cognitive and attentional effects familiar from behavioural psychology. For example, temporal sampling of the speech signal by delta, theta and gamma oscillations may be foundational in speech processing, packaging information into units of differing temporal granularity (such as “syllables” versus “phonemes”). Similarly, alpha oscillations are thought to play a key role in visual attentional selection and attentional control. Inhibition from ongoing alpha oscillations determines whether visual stimuli reach conscious awareness, thereby profoundly affecting visual attention. A “temporal sampling” framework offers a novel opportunity for theoretical integration in the field of dyslexia, which is currently fragmented by many competing causal theories, including theories based on core phonological, visual and attentional deficits. Recently, one possible conceptual framework exploring how atypical temporal sampling of auditory information could underpin the phonological (sound structure) deficit found in dyslexia across languages was proposed (Goswami, 2011). Goswami argued that a primary problem with auditory temporal sampling could cause the atypical development of speech-based representations from infancy, leading to the phonological difficulties that children with dyslexia experience in every language so far studied. She also argued that atypical auditory oscillatory function would have knock-on effects for visual and cross-modal processing in dyslexia, thereby affecting auditory attention and visual processing. Logically, it is also possible that the primary sampling difficulty in dyslexia could be visual, with knock-on affects for auditory processing, or that the primary problem could lie with a certain frequency band or bands, and have cross-modal effects. Further, it is possible that hierarchical cross-frequency coupling of oscillations is deficient in dyslexia. In oscillatory hierarchies, the activity of faster frequencies related to spike timing can be modulated by the activity of slower frequencies, which act to align neuronal excitability with high-information sections of the input. Atypical cross-frequency coupling of auditory-visual information could for example impair both visual and auditory attention in dyslexia. On the other hand, a deficit of this nature would be expected to have developmental effects on cognitive systems other than reading, and so consideration of how any postulated oscillatory difficulty would affect children’s developmental trajectories is absolutely critical for successful theory development.
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