Poor Reading: A Deep Dive
Causes of dyslexia
Root causes of dyslexia
Dyslexia arises from a combination of factors rather than a single cause. Research points to both genetic influences and neurocognitive differences as key contributors.
Phonological deficit
The most widely supported cause of dyslexia is a deficit in phonological processing – in other words, an impaired ability to analyze and manipulate speech sounds. This makes it difficult to link letters with their sounds and to “sound out” words, which is fundamental for reading and spelling. Many studies confirm that children with dyslexia perform poorly on phonemic awareness tasks (like deleting a sound from a word) compared to typical readers.
Genetic influence
Dyslexia often runs in families. Twin and molecular genetic studies have identified multiple genes (on chromosomes 1, 6, 15, and others) associated with reading difficulties. Heritability estimates for dyslexia range from ~40% up to 70%, indicating a strong genetic component. These genes are thought to influence brain development in areas critical for reading (such as those that support language and visual processing).
Brain differences
Brain imaging has revealed that dyslexic readers show reduced activation in left occipito-temporal regions (often called the “word form” area) during reading. This area is responsible for recognizing written words quickly. Additionally, differences are seen in the temporo-parietal areas involved in mapping letters to sounds. In some dyslexic individuals, the two hemispheres of the brain have more symmetrical activity during reading, whereas typical readers show a strong left-hemisphere dominance. These neurological differences underlie the reading and spelling difficulties.
Visual processing deficits (Magnocellular therory)
Apart from language processing, research has shown that some people with dyslexia have deficits in the fast visual processing pathway known as the magnocellular pathway. The magnocellular visual system handles the quick transmission of visual information (crucial for tracking moving text or scanning words). An abnormality here can cause reduced sensitivity to visual motion and flicker, leading to difficulties in keeping track of letters and words while reading. This can manifest as skipping words or lines, or seeing text “jump.” Not all dyslexics have this issue, but it represents a subset where visual therapies might help.
Auditory processing and timing deficits
Some evidence suggests subtle auditory processing impairments in dyslexia – specifically, difficulty processing fast changes in sounds. This auditory timing deficit can contribute to the phonological problems. In fact, the magnocellular theory extends to auditory magnocellular neurons as well: dyslexics may have less sensitive auditory temporal processing, which in turn affects phonological decoding. Thus, slow auditory processing could lead to trouble distinguishing similar phonemes, compounding reading problems.
Working memory and executive function
Dyslexia is also linked to weaknesses in working memory – the ability to hold and manipulate information in mind. For example, keeping a sequence of sounds or letters in memory may be harder, affecting decoding of longer words and spelling of longer words. Many dyslexic individuals have lower verbal working memory spans. They may also exhibit slower processing speed and difficulty with rapid automatized naming, indicating inefficiencies in the brain’s retrieval of learned information. These cognitive factors are not causes of dyslexia on their own but are common underlying deficits that exacerbate reading difficulties.
Other contributing factors
Attention disorders (like ADHD) are frequently comorbid with dyslexia, which can further impair reading by reducing focus and consistency. However, by itself, attention deficit is not a cause of dyslexia – rather, the two conditions sometimes co-occur. Additionally, developmental coordination or motor skill issues can co-occur (dyspraxia), which might affect handwriting. Importantly, dyslexia is not caused by poor teaching, low intelligence, or vision problems such as blurry sight. It is rooted in brain differences in language and processing, though visual stress (sensitivity to certain light or contrast) can aggravate reading in some cases – for those individuals, colored overlays or fonts sometimes provide minor relief (this is separate from core dyslexia causes and varies per individual).
Summary
Modern research favors a multiple-deficit model of dyslexia: rather than one single deficit, it is often the result of multiple subtle deficits across phonological, visual-attentional, and memory systems. One child with dyslexia might primarily have a phonological deficit; another might have a combination of a mild phonological deficit plus a visual attention weakness and slower processing speed. These different profiles explain why dyslexia can look different across individuals. Recognizing the various contributing causes in each person can help tailor more effective interventions.
Next up: When dyslexia meets dysgraphia
Two challenges, one common thread
Many kids experience both reading and writing difficulties. In our next article, learn how dyslexia and dysgraphia overlap—and how to support both without overwhelm.