Earlier this year Emeritus Professor of Physiology, John Stein, published a review in ‘Current Developmental Disorder Reports’ about visual dyslexia.
Developmental Dyslexia has become a rather controversial concept in recent years, and its very existence has been denied. The importance of children training in phonics has been greatly overemphasized and the crucial role of the visual processes that precede a child’s ability to gain phonological awareness has been forgotten. Yet until recently it was generally accepted that learning to sequence written text visually is a crucial first step in learning to read. Today there is little doubt that learning to recognize and sequence letters visually precedes the ability to grasp phonics. This fact was discovered nearly 50 years ago, and subsequent advances in neuroimaging, neuropsychology and molecular genetics have provided solid neuroscientific evidence for its truth.
But in the last few years the phonological theory of dyslexia (PT) has become dominant. It asserts that Developmental Dyslexia (DD) is due to a hereditary psycho-linguistic deficit causing difficulty with grasping the concept of phonemes. But this theory ignores nearly a century of research showing that proper development of the brain networks of visual magnocellular neurons (M- cells), that signal the timing of visual events, precedes and is essential for the development of phonological awareness.
In Professor Stein’s review, first the cerebral structures with which the visual M- system is associated for reading both alphabetic and logographic scripts are described, and he demonstrates how their development at each level from the eye to cortical visuomotor control networks, is impaired in DD. Then he reviews how M- cell function may be facilitated. The simplest way to improve it involves viewing text through yellow or blue filters and he discusses how these may work. Even simpler is to improve children’s nutrition; and he introduces some aspects of this. Some of the alleles of genes which are associated with the M- system have also been shown to play an important role in regulating the immune system; hence he considers how DD is associated with disordered control of inflammation and with autoimmune conditions such as lupus, asthma and eczema.
In conclusion, this review shows how there is now a great weight of evidence demonstrating that the development of rapid visual sequencing of text, mediated by the visual magnocellular timing system, is the first essential for learning to read, and that impaired development of this system is a major cause of Developmental Dyslexia. Furthermore, this understanding has led to the development of very simple and effective ways of improving M-cell function such as the use of blue or yellow filters and improved nutrition.
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