Study material - book

Etiology of SLD - history and current concepts in our country and in the world

Traditional division in modern form:

• Traditional model of SLD etiology according to O. Kučera (1961)
• Minor brain damage (MBD, formerly encephalopathy) - a neurological finding mentions more minor conspicuousness, the anamnesis points to possible brain damage in the prenatal, perinatal or postnatal period - 50% of individuals with SLD
• Hereditary etiology - history of typical occurrence of communication disorders in relatives - 20% of individuals with SLD
• Hereditary encephalopathic etiology - a combination of both previous types - 15% of individuals with SLD
• Neurotic or unclear etiology - 15% of individuals with SLD. Neurosis as a cause is incomparably rarer than neurosis as a consequence of SLD

1980s: neurological-biological etiology

Etiological factors

• interacting internal and external factors
• development of views on the causes of failures
• genetic factors ---> partial deficits
• Current etiological models: e.g.

• common significant etiological context
• deficits of partial functions
• risk types of laterality
• perceptual, motor, memory
• within MBD/ HKD/ ADHD

Neurobiological approach

• demonstrated the difference in the brain of dyslexics
• enabled by the development of imaging techniques since the 1980s.
• monitoring of normal and diseased structures and performance, especially in the left hemisphere
•  post-mortem analysis (dead brains) - prof. Galaburda
•  dyslexia as a disorder of neuronal migration
•  analysis by imaging methods - detected metabolic changes in various parts of the brain, identification of nerve circuits involved in reading, especially in the left hemisphere
• analysis of evoked potentials - monitoring of electrical reactions of the brain to a stimulus (word or picture), detection of intermodal deficit, good possibilities of prediction of dyslexic difficulties

Phonological model

I. Libermanová

• inverse concept replaced by language concept
• key concept of phoneme awareness

• the child needs phonemic awareness (segmentation) only in connection with reading,
• phoneme-grapheme relationship: complex process of character identification and sounding = grapheme - phoneme correspondence (disturbed in dyslexics)
• revealing the importance of short-term memory for reading and deviations in dyslexics (mainly in verbal memory)
• Libermanová: timely search for children at risk of reading according to differences in phoneme awareness and verbal short-term memory
• phonological skills: analysis, synthesis and short-term phonological memory

Double deficit theory (N. Geschwind)

• originated in the solution to phonological reeducation of resistant cases of dyslexia
• dyslexia is caused by two deficits: phonological awareness and rapid automated processing of stimuli
• problems in the sound processing itself and the resulting inability to create a link between the grapheme and the phoneme
• dyslexics are unable to perceive short or rapidly changing sounds.
• use of the quick naming test - detects visual-verbal discontinuity
• Norman Geschwind: founder of behavioral neurology

Theory of visual deficit

• pointed out the deficits, which were subsequently explained by magnocellular theory
• deals with the share of visual disorders in reading problems
• monitors deficits in the analysis and differentiation of visual perceptions
• emphasizes in particular unstable binocular fixations and incorrect perception of object boundaries, which leads to difficulties with processing letters and words on the text page, a specific deficit is the so-called iconic persistence (visual persistence)
• related mainly to abnormalities in the right hemisphere

Magnocellular theory

• in the brain there are two different nervous systems related to reading: magnocellular and parvocellular, controlled from the subcortical (thalamus) - transfers information to superior structures in the cerebral cortex
• magnocellular system (magnus = large, cellular = cellular) - strongly myelinated cells that transfer excitations well
• responsible for the speed and timeliness of information processing, allows vision in low light and low contrast, the system is sensitive to changes in time, predominates in peripheral vision
• parvocellular system (parvus = small)
• small cells capable of processing even small distances between stimuli
• specialized in color perception and detailed object viewing
• handles short words accurately when reading
• dyslexics are not able to process a large number of short visual stimuli in a small area, there is a merging of characters

Cerebellar theory

• seeks the cause of dyslexia in mild cerebellar dysfunction ensuring motor coordination
• Disruption of the cerebellum leads to reduced ability
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