Week 4 - Visual stress and dyslexia Flashcards
Incidence and description of dyslexia
• Between 10-20% of population of school children
- No uncorrected deficiencies in hearing and or vision
• Discrepancies between intelligence and reading ability
- Often children overcompensate and mask symptoms
• Dyslexia is present when all other aspects of development are normal but reading/ spelling delayed
• Many of features of dyslexia are found in normal readers in the early stages of development of reading
• Primarily a literacy difficulty with difficulty converting letters into sounds
Reading Difficulties: “Phonology”
• Poor alphabetic coding skills : deficient ability to learn letter sounds and to decode words phonetically (e.g., “at” in “cat”, “fat”, “rat”).
• Deficient ability to identify (name) words as wholes as observed in letter by letter, sound by sound approach to word identification and a general tendency to be overly analytical.
• Poor alphabetic coding skills and poor ability to identify words as wholes
Processing problems: evidence
• Most severely impaired readers are deficient in alphabetic coding.
• Smaller percentages tend to be deficient only in whole word identification or only in alphabetic coding.
• The most severely impaired readers are deficient in both alphabetic coding and whole word identification.
What areas of the brain are responsible for what?
• Angular Gyrus: Sound-symbol associations
• Broca’s Area: Speech sound awareness (phenological processor)
• Wernicke’s Area: Language comprehension (context and meaning processors)
• Occipital lobe: Letter and letter-pattern recognition; storage of printed word images
Signs and symptoms:
• Visual perception and spatial confusion deficits:
- letters and words as reversed forms (“seeing” b as d or was as saw); general spatial orientation problems.
• Imperfect representation of letters, spelling patterns, and whole words and poor memory for visual detail I.e Template matching
Visual processing difficulties: deficit types
• Oculomotor deficits Eve movements/saccades, conversion, and fusion defects that impair form perception and left to right scanning.
- Evidence suggests this is trained, poor ability therefore likely to indicate lack of practice
• Magnocellular deficit. Fast processing, temporal or timing responsibilities, smooth pursuit, eye movement control, bv control, timing of saccades but not stimulated by high contrast ?? Role in reading
• Noise deficit theory over activity in cortex interferes with processing, lack of ability to inhibit cortical processes - too much activity in the brain. This can be improved with coloured overlays to reduce the “noise”
Visual cortex association with reading:
Primary Visual cortex
• Ventral stream allow discrimination of shapes and objects
• Dorsal stream responsible for visual guiding/grasping at objects
• 80% of learning is done through vision
• 40% of brain is dedicated to processing visual input
Structures involved in reading:
•Dorsal visual stream- where pathway
• Ventral visual stream- what pathway
• Corpus Callosum
• Magnocellular cells
• Oculomotor control
• Binocular vision
• Fixation control
• Visual Perception
How can poor vision affect reading?
• Blurry vision can affect ability to see letters and words accurately
• Discomfort or pain may make reading unpleasant
• Motivation: Poor vision may affect motivation since comprehension poorer therefore does achieve goals of reading
- Frustration
- Already compounds other errors made during reading
What is visual stress?
• Visual stress is also known as the “Meares-Irlen” syndrome and the condition generally refers to reading difficulties, light sensitivity and headaches from exposure to disturbing visual patterns or print distortion.
What is visual discomfort?
• Visual discomfort and perceptual distortions and the benefit from color are sometimes collectively referred to as ‘visual stress’ or ‘Meares-Irlen Syndrome’, and sometimes as ‘Irlen Syndrome’ (USA), or (formerly) ‘scotopic sensitivity syndrome’
Common symptoms: visual stress
• Moving words on a page
• Jumbling of words
• Poor Convergence
• Poor accommodation
• Diplopia
• Asthenopia
• Headaches mostly frontal
• Skipping words on the page
• Losing place frequently
•Struggling to copy from the boardReader moves/wriggles a lot!
Full orthoptic/Bv Assessment:
• Fixation and alignment
• Binocular status
• Fixation Disparity
• Convergence - jump and push up
• Accommodation, amplitude, facility and accuracy
• Fusional reserves
• Saccades
• Smooth Pursuit
• Tracking
• Dynamic Retinoscopy
• Rate of Reading Test with and without colour
What tests can be done to investigate visual stress/dyslexia
• Dynamic retinoscopy
• Rate of reading test
• Development eye movement test
• Overlays
• Colimetry
• Cerium lenses
Describe DEM : Development eye movement
•DEM is a psychometric test that enables us to assess ocular movement in a reading like condition
• Remember reading involves many saccades
• This allows a measure of speed and accuracy
• DEM alone cannot detect visual stress
