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Neurological Basis of Dyslexia

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Cecilia Marcano
Cecilia Marcano

Dyslexia is a neurological disorder with a genetic origin. There are three major theories about its causes: the phonological theory involving phonological representations, the auditory theory involving perception of short/rapid sounds, and the visual theory involving processing of letters and words. The cerebellar theory also suggests the cerebellum plays a role in motor control and automatization of tasks like reading. A unifying magnocellular theory attempts to integrate these findings by proposing a generalized magnocellular dysfunction across modalities that also affects the cerebellum. While its exact mechanisms remain unclear, dyslexia is not a disease and interventions aim to improve coping skills in a society where reading and writing are integral.

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Neurological Basis of Dyslexia
Is a specific learning disabilities in reading is often characterized by difficulties with accurate word recognition, decoding and spellingmay cause problems with reading comprehension and slow down vocabulary growth. is not the result of poor instruction is not linked to intelligence
the child, despite having normal intelligence and receiving proper teaching and parental support, has difficulty learning to read. Learning to read the child learns to crawl, walk, talk, throw or catch things, ride a bicycle later than the majority of other kids. Milestones reached later apart from being slow to learn to speak, the child commonly mispronounces words, finds rhyming extremely challenging, and does not appear to distinguish between different word sounds. Speech at school the child takes much longer than the other children to learn the letters of the alphabet and how they are pronounced. There may also be problems remembering the days of the week, months of the year, colors, and some arithmetic tables. Slow at learning sets of data the child may seem clumsier than his or her peers. Catching a ball may be difficult. Coordination the child commonly gets "left" and "right" mixed up. Left and right numbers and letters may be reversed without realizing. Reversal may not follow a pattern of progression seen in other children. One word may be spelt in a variety of ways on the same page. Spelling phonology refers to the speech sounds in a language. If a word has more than two syllables, phonology processing becomes much more difficult. Phonology problems children with dyslexia commonly find it hard to concentrate for long, compared to other children. Concentration span More about dyslexia
It is now well established that dyslexia is a neurological disorder with a genetic origin. FMRI and behavioral experiments have generated significant results so as to suggest the disorder be viewed as having neurological causes. Neurological research has uncovered clear evidence of biophysical and structural anomalies in individuals who are affected.
But its actual mechanisms are still mysterious and currently remain the subject of intense research endeavour in various neuroscientific areas and along several theoretical frameworks. . Indeed, there are no less than three major theories of dyslexia.
Explains that the origin of the disorder is a congenital dysfunction of lefthemisphere perisylvian brain areas underlying phonological representations, or connecting between phonological and orthographic representations. Bradley and Bryant (1978)
The phonological theory postulates that dyslexics have a specific impairment in the representation, storage and/or retrieval of speech sounds. Dyslexics reading impairment by appealing to the fact that learning to read an alphabetic system requires learning the graphemephoneme correspondence If these sounds are poorly represented, stored or retrieved, the learning of graphemephoneme correspondences, the foundation of reading for alphabetic systems, will be affected accordingly
Specifie that the primary deficit lies in the perception of short or rapidly varying sounds. The original version of the auditory theory made no particular claim at the biological level, but abnormal neurophysiological responses to various auditory stimuli have also been demonstrated. Tallal and Piercy (1973)
Support for this theory arises from evidence that dyslexics show poor performance on a number of auditory tasks, including frequency and temporal order judgement. The failure to correctly represent short sounds and fast transitions would cause further difficulties in particular when such acoustic events are the cues to phonemic contrasts. There is indeed also evidence that dyslexics may have poorer categorical perception of certain contrasts
A visual impairment giving rise to difficulties with the processing of letters and words on a page of text. This may take the form of unstable binocular fixations, poor vergence or increased visual crowding. Logrelove et al (1980)
The visual theory does not exclude a phonological deficit, but emphasizes a visual contribution to reading problems, at least in some dyslexic individuals The theory postulates that the magnocellular pathway is selectively disrupted in certain dyslexic individuals, leading to deficiencies in visual processing, and, via the posterior parietal cortex, to abnormal binocular control and visuospatial attention.
Here the biological claim is that the dyslexics cerebellum is mildly dysfunctional and that a number of cognitive difficulties ensue. Evidence of poor performance of dyslexics in a large number of motor tasks in dual tasks demonstrating impaired automatization of balance, and in time estimation, a nonmotor cerebellar task, is shown by brain imaging studies, they have also shown anatomical, metabolic and activation differences. Nicolson and Fawcett (1990)
Cerebellum plays a role in motor control and therefore in speech articulation. It is postulated that retarded or dysfunctional articulation would lead to deficient phonological representations Cerebellum plays a role in the automatization of overlearned tasks, such as driving, typing and reading. A weak capacity to automatize would affect, among other things, the learning of graphemephoneme correspondences.
Finally, there is a unifying theory that attempts to integrate all the findings mentioned above. A generalization of the visual theory, the magnocellular theory postulates that the magnocellular dysfunction is not restricted to the visual pathways but is generalized to all modalities (visual and auditory as well as tactile). Furthermore, as the cerebellum receives massive input from various magnocellular systems in the brain, it is also predicted to be affected by the general magnocellular defect. Stein and Walsh (1997)
Through a single biological cause, this theory therefore manages to account for all known manifestations of dyslexia: visual, auditory, tactile, motor and, consequently, phonological. Beyond the evidence pertaining to each of the theories described previously, evidence specifically relevant to the magnocellular theory includes magnocellular abnormalities in the medial as well as the lateral geniculate nucleus of dyslexics brains, poor performance of dyslexics in the tactile domain and the cooccurrence of visual and auditory problems in certain dyslexics
Dyslexia is not a disease. We live in a society where reading and writing are integral parts of everyday life - interventions that help people with dyslexia are aimed at improving their coping skills. Some people claim that dyslexia is part of our differences, here is a nice video about it.

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Neurological Basis of Dyslexia

  • 2. Is a specific learning disabilities in reading is often characterized by difficulties with accurate word recognition, decoding and spellingmay cause problems with reading comprehension and slow down vocabulary growth. is not the result of poor instruction is not linked to intelligence
  • 3. the child, despite having normal intelligence and receiving proper teaching and parental support, has difficulty learning to read. Learning to read the child learns to crawl, walk, talk, throw or catch things, ride a bicycle later than the majority of other kids. Milestones reached later apart from being slow to learn to speak, the child commonly mispronounces words, finds rhyming extremely challenging, and does not appear to distinguish between different word sounds. Speech at school the child takes much longer than the other children to learn the letters of the alphabet and how they are pronounced. There may also be problems remembering the days of the week, months of the year, colors, and some arithmetic tables. Slow at learning sets of data the child may seem clumsier than his or her peers. Catching a ball may be difficult. Coordination the child commonly gets "left" and "right" mixed up. Left and right numbers and letters may be reversed without realizing. Reversal may not follow a pattern of progression seen in other children. One word may be spelt in a variety of ways on the same page. Spelling phonology refers to the speech sounds in a language. If a word has more than two syllables, phonology processing becomes much more difficult. Phonology problems children with dyslexia commonly find it hard to concentrate for long, compared to other children. Concentration span More about dyslexia
  • 4. It is now well established that dyslexia is a neurological disorder with a genetic origin. FMRI and behavioral experiments have generated significant results so as to suggest the disorder be viewed as having neurological causes. Neurological research has uncovered clear evidence of biophysical and structural anomalies in individuals who are affected.
  • 5. But its actual mechanisms are still mysterious and currently remain the subject of intense research endeavour in various neuroscientific areas and along several theoretical frameworks. . Indeed, there are no less than three major theories of dyslexia.
  • 6. Explains that the origin of the disorder is a congenital dysfunction of lefthemisphere perisylvian brain areas underlying phonological representations, or connecting between phonological and orthographic representations. Bradley and Bryant (1978)
  • 7. The phonological theory postulates that dyslexics have a specific impairment in the representation, storage and/or retrieval of speech sounds. Dyslexics reading impairment by appealing to the fact that learning to read an alphabetic system requires learning the graphemephoneme correspondence If these sounds are poorly represented, stored or retrieved, the learning of graphemephoneme correspondences, the foundation of reading for alphabetic systems, will be affected accordingly
  • 8. Specifie that the primary deficit lies in the perception of short or rapidly varying sounds. The original version of the auditory theory made no particular claim at the biological level, but abnormal neurophysiological responses to various auditory stimuli have also been demonstrated. Tallal and Piercy (1973)
  • 9. Support for this theory arises from evidence that dyslexics show poor performance on a number of auditory tasks, including frequency and temporal order judgement. The failure to correctly represent short sounds and fast transitions would cause further difficulties in particular when such acoustic events are the cues to phonemic contrasts. There is indeed also evidence that dyslexics may have poorer categorical perception of certain contrasts
  • 10. A visual impairment giving rise to difficulties with the processing of letters and words on a page of text. This may take the form of unstable binocular fixations, poor vergence or increased visual crowding. Logrelove et al (1980)
  • 11. The visual theory does not exclude a phonological deficit, but emphasizes a visual contribution to reading problems, at least in some dyslexic individuals The theory postulates that the magnocellular pathway is selectively disrupted in certain dyslexic individuals, leading to deficiencies in visual processing, and, via the posterior parietal cortex, to abnormal binocular control and visuospatial attention.
  • 12. Here the biological claim is that the dyslexics cerebellum is mildly dysfunctional and that a number of cognitive difficulties ensue. Evidence of poor performance of dyslexics in a large number of motor tasks in dual tasks demonstrating impaired automatization of balance, and in time estimation, a nonmotor cerebellar task, is shown by brain imaging studies, they have also shown anatomical, metabolic and activation differences. Nicolson and Fawcett (1990)
  • 13. Cerebellum plays a role in motor control and therefore in speech articulation. It is postulated that retarded or dysfunctional articulation would lead to deficient phonological representations Cerebellum plays a role in the automatization of overlearned tasks, such as driving, typing and reading. A weak capacity to automatize would affect, among other things, the learning of graphemephoneme correspondences.
  • 14. Finally, there is a unifying theory that attempts to integrate all the findings mentioned above. A generalization of the visual theory, the magnocellular theory postulates that the magnocellular dysfunction is not restricted to the visual pathways but is generalized to all modalities (visual and auditory as well as tactile). Furthermore, as the cerebellum receives massive input from various magnocellular systems in the brain, it is also predicted to be affected by the general magnocellular defect. Stein and Walsh (1997)
  • 15. Through a single biological cause, this theory therefore manages to account for all known manifestations of dyslexia: visual, auditory, tactile, motor and, consequently, phonological. Beyond the evidence pertaining to each of the theories described previously, evidence specifically relevant to the magnocellular theory includes magnocellular abnormalities in the medial as well as the lateral geniculate nucleus of dyslexics brains, poor performance of dyslexics in the tactile domain and the cooccurrence of visual and auditory problems in certain dyslexics
  • 16. Dyslexia is not a disease. We live in a society where reading and writing are integral parts of everyday life - interventions that help people with dyslexia are aimed at improving their coping skills. Some people claim that dyslexia is part of our differences, here is a nice video about it.