The visual basis of reading and reading difficulties

Abstract

Most of our knowledge about the neural networks mediating reading has derived from studies of developmental dyslexia (DD). For much of the 20th C. this was diagnosed on the basis of finding a discrepancy between children’s unexpectedly low reading and spelling scores compared with their normal or high oral and non-verbal reasoning ability. This discrepancy criterion has now been replaced by the claim that the main feature of dyslexia is a phonological deficit, and it is now argued that we should test for this to identify dyslexia. However, grasping the phonological principle is essential for all learning to read; so every poor reader will show a phonological deficit. The phonological theory does not explain why dyslexic people, in particular, fail; so this phonological criterion makes it impossible to distinguish DD from any of the many other causes of reading failure. Currently therefore, there is no agreement about precisely how we should identify it. Yet, if we understood the specific neural pathways that underlie failure to acquire phonological skills specifically in people with dyslexia, we should be able to develop reliable means of identifying it. An important, though not the only, cause in people with dyslexia is impaired development of the brain’s rapid visual temporal processing systems; these are required for sequencing the order of the letters in a word accurately. Such temporal, “transient,” processing is carried out primarily by a distinct set of “magnocellular” (M-) neurones in the visual system; and the development of these has been found to be impaired in many people with dyslexia. Likewise, auditory sequencing of the sounds in a word is mediated by the auditory temporal processing system whose development is impaired in many dyslexics. Together these two deficits can therefore explain their problems with acquiring the phonological principle. Assessing poor readers’ visual and auditory temporal processing skills should enable dyslexia to be reliably distinguished from other causes of reading failure and this will suggest principled ways of helping these children to learn to read, such as sensory training, yellow or blue filters or omega 3 fatty acid supplements. This will enable us to diagnose DD with confidence, and thus to develop educational plans targeted to exploit each individual child’s strengths and compensate for his weaknesses.

Alterations in neural activation in the ventral frontoparietal network during complex magnocellular stimuli in developmental dyslexia associated with READ1 deletion

“…The right frontoparietal system is a crucial component of the network subserving the automatic shifting of attention [89,90], and developmental changes in its activation have been linked to reading skills in both children with DD [91,92] and TRs [93]. Accordingly, alterations in M input processing in the dorsal visual stream and a consequent dysfunction of the main frontoparietal attentional network, are associated with a sluggish attentional shifting (SAS) [86] and a deficit in perceptual noise exclusion [82,83] in DD [48,52,53,94]. Irrelevant lateral letters should be filtered out by accurate and rapid shifts in spatial and temporal visual attention before the letter-to-sound mapping mechanism is applied [95][96][97][98][99][100][101][102].…”

Visual-attentional and phonological deficits explored in French dyslexic students: eye movements recorded during a phonological lexical decision task

“…They were created from words by changing one grapheme at a time; *chuse); (4) Consonant strings (CS; sequences that are orthographically illegal and phonologically unpronounceable, since they contain no vowels and therefore no syllables; *nbvrzc). Consonant strings were matched with words based on their form, with respect to the ascender or descender graphemes that they contain; (5) Symbol strings (SS; non-alphabetic stimuli; § ¥Đ ‡). Symbol strings were matched for the number of characters with high frequency words.…”

“…The main cause of dyslexia is considered to be the phonological de cit, i.e., a di culty in the use of grapheme-to-phoneme conversion rules [1][2][3] . However, many researchers query whether a phonological de cit is the only cause of dyslexia [4][5][6] . Other theories such as auditory de cits 7 , working memory impairment 8 , attentional abnormalities 9 and magnocellular abnormalities 10 have been proposed as alternative explanations.…”

Duration Perception and Reading in Typically Developing Adults and Adults with Developmental Dyslexia: Implications for Assessment and Intervention

“…Individuals with dyslexia exhibit impaired time perception across a diverse range of tasks [ 7 ]. Compared to typically developing (TD) controls, children with dyslexia (DD) display increased inaccuracy and variability in beat-related tasks [ 3 ], inconsistencies in the neural representation of auditory beats [ 8 ], as well as reduced neural synchronization (entrainment) to visually [ 9 ] and multimodally presented rhythms [ 10 ]. Correlational studies have indicated that beat perception is associated with performance in reading and reading-related tasks, such as pseudoword decoding [ 11 ], Rapid Automatized Naming [ 11 , 12 , 13 ], phonological awareness [ 14 , 15 ], and letter-to-sound knowledge [ 15 ], in both TD individuals and those with dyslexia [ 16 , 17 ].…”