Dyslexia Flashcards
Dyslexia definition (DSM)
A person having a specific learning disability with impairment in reading, when reading achievement, as measured by individually administered standardised tests of reading accuracy or comprehension, is substantially below that expected given the person’s chronological age, measured intelligence, and age-appropriate education.
Shorter dyslexia definition
A pattern of learning difficulties characterized by problems with accurate or fluent word recognition, poor decoding, and poor spelling abilities.
How common is dyslexia? (Rutter et al, 2004; Rose, 2009)
Rutter - Affecting about 3- 6% of children, with more boys than girls
Rose - Prevalence is variable
Symptoms of dyslexia in pre-school
Delayed speech development
Speech problems e.g. jumbling up phrases
Little appreciation of rhyming words
Difficulty learning the alphabet
Symptoms of dyslexia in school children
Problems learning names and sounds of letters
Unpredictable and inconsistent spelling
Confusing the order of letters in words
Making errors when reading aloud
Struggling to learn sequences e.g. days of the week
Poor handwriting
Taking longer than normal to complete written work
How is dyslexia diagnosed?
- Rule out other issues with vision, hearing and other conditions like ADHD
- Parents and teachers supply general health, developmental and medical history and how a child performs on certain tasks
- Child completed a set of cognitive measures assessing IQ, reading, writing, language, memory, reasoning and processing speed
Pennington and Smith (1988)
40% of boys and 18% of girls with a dyslexic parent are also dyslexic
DeFries et al (1987)
Concordance rate is higher in identical twins than non-identical twins
Cardon et al (1994)
Shorter genes on chromosome 6 could be a cause for dyslexia
Grigorenko et al (2001)
The language part of the brain is smaller than neurotypical in dyslexic people
Brunswick et al (1999)
Compared dyslexics to controls during reading, less activation in the left inferior and middle temporal lobe, left frontal operculum, and cerebellum in dyslexics
Paulesu et al (1996)
When rhyming, those with dyslexia showed less activation in Wernicke area and left insula. This suggests a disconnection between posterior and frontal language areas
Environmental factors of dyslexia
- Poor SES
- Lack of literacy related skills at home
- Lack of schooling
- Different languages
Languages and dyslexia
Some languages have regular sound-spelling correspondences, and this limits dyslexia.
Poor performance tasks for dyslexics
- Single word reading
- Word Recall (a verbal short-term memory task)
Three aspects of reading
Semantics
Orthography
Phonology
Phonology definition
Skills that involve dealing with speech sounds
Skills in phonology
Implicit skills – Skills that are automatically engaged (verbal short-term memory, Rapid Automatised naming)
Explicit skills – Skills related to reflecting upon and/or manipulating speech sounds (phonological awareness / sensitivity)
Bradley and Bryant (1983)
Followed 400 children from aged 4 to 8
Children’s phonological awareness at aged 4 was a good predictor of reading and spelling at aged 8, even when controlling for IQ, memory and social class
Manis et al (1993)
Those with dyslexia show poorer performance than controls on phonological awareness tasks e.g. rhyme tasks
Snowling et al (1986)
Dyslexic people show poorer performance on simple phonological processing tasks like nonword repetition and
picture naming
Wolf and Bowers (1999)
Dyslexics have deficits in automised naming
Hulme (1981)
Children with dyslexia have been found to have impaired verbal short-term memory, but in tact visual short-term memory
Visual Perceptual Theory
Reading requires recognition of letters and conversions to sounds (called grapheme-phenome mapping).
The magnocellular visual pathway is responsible for this task between the eyes and the brain. They also detect contrast, motion, and rapid changes in the visual field.
For dyslexic people, retinal images persist longer than appropriate, resulting in an excess of visual information that creates a masking effect and a reduction in visual acuity.
There is a lack in the parvocellular pathway as well.
Stein (2019) - Magnocells in the retina
In neurotypical people, a static object can begin to jitter because of the Magnocells. The period of jitter is short for dyslexics
Stein (2019) - Magnocells in the Lateral Genicular Nucleus.
Post-mortem studies (and now structural MRI studies) have revealed thinner Magnocell layers in the LGN in dyslexics compared to controls.
Stein (2019) - Magnocells in the Striate Cortex
Dyslexics show significantly different performance on the flicker fusion task
Stein (2019) - Cortico magno systems.
The visual motion area V5 is active during visually guided movement. In dyslexics the activity in response to moving stimuli is reduced
Stein (2012)
90% of studies since 2000 examining magnocellular impairments in dyslexia had found some supportive evidence
American Academy of Pediatrics (2009)
“Any possible magnocellular deficit has insufficient evidence on which to base treatment”
Franceschini et al (2012)
Tested children on 2 visuospatial tasks: visual search and spatial cuing. Children who showed worse performance were the worst readers.
Bosse et al (2007)
There is a bigger difference in the visual attention span
Saksida et al (2016)
Deficits in visual attention span may only affect a small proportion of individuals with dyslexia
Nicolson and Fawcett (1990)
Problems in the automatization of new skills are at the core of the difficulties dyslexic children experience
Rae et al (1998)
Dyslexics show abnormal cerebellar anatomy and chemistry
Stoodley and Stein (2011)
Dyslexics have impaired activation of the cerebellum during reading
Leiner (1993)
fMRI under-activation of the cerebellum is the most reliable distinction of all MRI studies comparing dyslexics with controls
Moore et al (2017)
There is a close correlation between cerebellar volume measured in infancy and people’s eventual reading ability
Interventions (Vaughn and Roberts, 2007)
- Phonemic awareness
- Phonics
- Spelling/writing
- Fluency
- Vocabulary
- Comprehension
Coloured filters (Stein, 2019)
A convenient way of enhancing M- cell function is simply to view text through filters that selectively transmit yellow light
Can be either yellow or deep blue
Yellow filters (Harries et al, 2015; Ray et al, 2005)
¼ of dyslexics can improve their visual symptoms, motion sensitivity, vergence eye control and, most importantly, their reading, by using such yellow filters
Hankins et al (2008)
The yellow paper might help not because of the Magnocells, but by activating the recently discovered set of retinal ganglion cells which contain melanopsin
Bachmann and Mengheri (2018)
Common to use different fonts to help dyslexic people
Dawson et al (2019)
Assistive technologies eg Ease of Access also help dyslexics.
