Dyslexia is defined as a difficulty interpreting letters and numbers in a child with otherwise normal intelligence. In my previous blogpost I discussed the importance of the cerebellum in literacy and learning. Here I would like to discuss three other theories about dyslexia and link its importance to assessment and treatment.
Phonology refers to the sounds that comprise words. Whilst the English language has 26 letters in the alphabet, there are 44 sound unites, or phonemes, that can be used to construct words. The human brain is specialised to decode these speech sound, a process that starts in early infancy.
In dyslexia, however, decoding speech sounds does not occur automatically, and children with dyslexia can often be late talkers. In others, oral language may develop appropriately but a child finds it difficult to map these sounds onto letters, called sound-letter correspondence. This difficulty mapping speech sounds or phonemes to letters are called poor phonological awareness.
Phonological awareness is an umbrella term to describe a range of problems with speech-sound awareness and manipulation.
- being able to say the letters of the alphabet but not recognise it in print,
- confusing the shape of letters in the alphabet (‘b’ and ‘d’ for example),
- not being able to map compound sounds onto grapheme–phoneme correspondence (i.e.’sh’ in shame or ‘sc’ in scene), using simple sounds instead, i.e. phonetic writing (seen for scene, or same for shame),
- not able to break down words into their phonemic units (bake into ba-ke),
- difficulties with sound blending (pat without the ‘p’ is at or replacing ‘c’ with ‘f’ in cat is fat)
- difficulties with rhyming.
While these examples may be age-appropriate in the foundation years, its persistence over time and poor progress with phonology, should be a red flag to parents.
Why does this happen?
There are many reasons why children may struggle with phonological awareness, even in cases where oral language skills are well- if not over-developed.
- Genetic factors: it is now well-established that dyslexia is hereditary. There is a 40% chance that a child will have dyslexia if the father is dyslexic. Interestingly, research has identified chromosome 6 as one of the dyslexic genes, which are in the same area as autoimmune diseases (which often co-occur with dyslexic children), as well as chromosomes 15 and 18 associated with reading deficits.
- Glue ear: auditory discrimination may be affected in children who had recurrent or chronic ear infections in early childhood. This can have a significant impact on babies and toddlers as the brain is primed for sound discrimination, tone and accent at this age. It is usually only when these children fail to start talking that their hearing problems are identified.
- High-tone hearing loss: viral infections, ear infections, chemotherapy, steroids, environmental toxins and exposure to very loud noise early in life can affect the very fine hairs in the ear canal, the nerve receptors for hearing. These receptors vibrate at different frequencies which is interpreted by the brain as sound. Damage to the hairs or how the vibrations fall on the ear drum affect what sounds can be decoded by the brain. Often high frequency sounds, i.e. sounds in the ‘f’,‘sh’ and ‘t’ range cannot be heard properly and thus not mapped onto grapheme units.
Double deficit – speed and phonology
Some children with poor phonological awareness may also have slow naming speed. This is referred to as the double deficit in that access to speech sounds are delayed and these children often struggle to formulate what they want to say. This is thought to be due to poor connectivity in the white matter linking the temporal lobe with the frontal areas and is illustrated in diagram 1 below.
The blue and purple areas represent the semantic language area. It translates what is seen and heard into meaning. This information is sent to the frontal lobe for action (illustrated by the red, purple and blue arrows) and poor connectivity between these regions can affect output i.e. how fast someone can generate words, write something down or organise their thoughts.
Diagram 1: Connectivity and language image source
In children, there is evidence that gross and fine motor development may be linked to language development because the brain region for access (BA 44 in diagram) sits within the motor cortex. This is why children with balance and coordination problems can often have language difficulties.
There is a certain type of dyslexia associated with the visual system. These children may find it extremely difficult to read, both single words and sentences even when phonological processing is intact. They complain of eye strain, wobbling text or blurred vision (even when they can see normally). This can be associated with a weak magnocellar system.
Types of cells
There are two types of cells in the sensory system: magnocells which translate information about movement and contrast and parvocells which code for detail and colour. In the retina, these cells line the nerve track to the visual area in the brain. This is illustrated by diagram 2 below. The red arrows show the magnocellar pathway and the blue arrows the parvocellar pathway. Link it to diagram 1 above and you can see that the parvocells are linked to the semantic system, i.e. identifying what something is by decoding its form and colour (i.e. identify and name what you see). The magnocellar system codes for depth and motion, i.e. where something is in space and time, and links to the parietal system where all visual-spatial information is decoded. Both need to work together in vision the parvocells identifying what it is whilst the magnocells telling you where it is. Its also important in reading as the parvocells identify letters whilst the magnocells holds the image static whilst your eyes move across the page.
Diagram 2: Magnocells and parvocells in the retina image source
In children with a weak magnocellar system, the brain cannot hold the image static as the eyes track along the page. Text appears wobbly, blurry, run off the page or wavy and they may struggle to read even basic words such as (cat). They may have poor convergence (double vision), and can be sensitive to glare, contrast, and reflection resulting in inconsistent reading (good on some days and bad on others). Visual strain, headaches and migraines may also occur.
Spelling and writing may be significantly impaired as they have difficulty maintaining their position on a page and may show letter and number rotations, inversions and writing large then small. Attentional problems can occur as these children cannot hold an image stable as a focus for attention. Looking at the blackboard and then writing what they see poses specific challenges and can result in incomplete work, poor grasp of what is required of them and a disorganised approach to schoolwork. These children may be treated for ADHD with limited success.
Sensory motor system
Magnocellar weakness may affect the entire sensory motor system and is linked to how movement and depth are interpreted for all the sensory systems. It can account for the range of problems seen in some children with dyslexia, notably the visual system (eye tracking and reading), the auditory system (phonological processing), the motor system (balance and coordination) and kineastetic processing (proprioception)
Diagram 3:Sensorymotor system and dyslexia image source
OK so what can we do about this?
A good neuropsychological assessment is required to understand the brain mechanisms underlying behavioural and learning difficulties. There is not one type of dyslexia and knowing that a child has dyslexia is not enough! Whilst educational assessments can diagnose dyslexia, neuropsychological assessment is needed to know where the problem is in the brain and what can be done about it.
Treating phonological processing difficulties
Specific tests to examine phonological processing and awareness need to be done to understand the lev level exist the following may be needed. In addition, the following may help:
- A hearing test first!
- Address poor automaticity with over-learning. Dyslexics of the phonological type need to be taught phoneme-grapheme relationships, it doesn’t happen automatic. A good phonics program as part of an intensive remedial package may help.
- Sight reading may overcome difficulties with decoding letters and sounds. Dyslexics often have very good memory and by using their memory system to identify words (both regular and irregular, easy and difficult) may reduce their reliance on phonemic decoding.
- Context and meaning are needed to help them understanding what is going on in the text. Dyslexics often guess words, therefore a good vocabulary to understand what they read, even though the mechanics of reading may be poor, is crucial.
- Spell-checkers are handy. There are spell-check software specific to dyslexics and this should be considered an option in middle childhood. Your child may never write properly, but empower him/her to remain engaged with story-telling and literacy by letting technology take over the mechanical bits he/she cannot do so well.
- These children may always need help with form-filling, essays and CV’s but there is no reason why they should not become successful in life – in fact some of the most successful entrepreneurs are dyslexic, including Richard Branson, Henry Ford and Ted Turner.
Treating naming difficulties
Specific assessment may be necessary to tackle why and on what level a child may have difficulties accessing language. Do they have a poor vocabulary? Do they know the word but cannot get it out? Do they have additional motor problems, i.e. clumsy, coordination or articulation problems? If the problem is on an oral motor programming level than a speech and language therapist may help. If the problem includes all motor planning, including writing and kinaesthetic integration, an occupational therapist may be needed.
Addressing magnocellar weakness
The level of intervention depends on the level of the problem. In children with visual form of dyslexia, phonological awareness is often normal on testing, in these cases dealing with the visual spatial deficits of wobbly text, glare, reflection, double vision and eye strain can be tackled by behavioural optometry.
Coloured filters to reduce glare, contrast and movement can work well in cases where wavy text is an issue. Yellow and blue filters have been shown to improve binocular vision due to poor convergence (eye muscles working together to focus on the same point). Blue filters are often preferred as it is thought that yellow can make migraines worse (see www.slideshare.net: John Stein, Wobbles, warbles and fish). A behavioural optometrist can determine the exact tint for your child.
Interestingly, 50% of the sheath that covers the magnocellar cells consists of a long chain omega 3 fatty acid (DHA) and supplementation with omega 3 (not 6 and 9!) has been shown to improve reading in dyslexic children. Other studies link omega 3 to improvement in visual eye tracking, auditory discrimination, balance, coordination, attentional functions and reduced aggressive behaviours.
Lastly, there is a small group of children likely to suffer from sensory integration difficulties, where magnocellar weakness are likely to affect the entire sensory system as shown in diagram 3. In these cases a range of problems are present and these children can often be diagnosed with multiple learning disabilities, including ADHD and childhood depression. Occupational therapy may be needed to strengthen the entire visual-motor and visual-spatial system, improving balance, coordination and proprioception. In these cases, allergies, food sensitivities and auto-immune disorders may also occur and holistic management of health, cognitive and physical development is needed.
In this blog I demonstrated the many faces of dyslexia and that treatment need to focus on the particular type and kinds of problems a child presents with. It is not enough to say, yes a child is dyslexic, it is important to identify the brain mechanisms underpinning those difficulties. A comprehensive neuropsychological assessment focusing on the key language systems can elucidate this.