Overview

Dyslexia is a learning disability that typically affects children who struggle with literacy in all formats, but it can also develop later in life as a result of injury.¹ Dyslexia affects the cognitive processes associated with spelling and reading, but it also affects many other aspects of information processing.² Each person with dyslexia has a unique set of symptoms that do not impair their intelligence or learning abilities when accommodations are in place (British Dyslexia Association).³

Types of dyslexia

Developmental dyslexia

This form of dyslexia, typically identified during childhood, is hereditary and present from birth. Common traits include weaker listening comprehension, smaller vocabulary, and delayed speech development. Around 7% of the population is developmentally dyslexic.³

Acquired dyslexia

Acquired dyslexia occurs later in life, often after traumatic brain injuries that impact the brain's language-processing areas. Two notable forms of acquired dyslexia are surface dyslexia and deep dyslexia:

• Surface dyslexia: affects the ability to recognise whole words, particularly irregular words, relying instead on phonetic decoding.
• Deep dyslexia: a severe version of acquired dyslexia, disrupts word phonetics and visual word recognition, significantly reducing the ability to read.⁴

Reading impairment

Individuals with dyslexia often experience difficulty decoding written words. This results in problems with word recognition, phonetic separation, and ‘sounding out’ of words. These problems commonly arise from phonetic or visuospatial difficulties.^5,6 Subsequently, there is a reduction in the accuracy and speed of reading, commonly reading in a slow and disjointed manner to compensate for their difficulties. Spelling and writing fluency and comprehension also suffer due to these functions.³

The difficulty in recognising symbols can translate to mathematics sometimes, resulting in problems with recognising mathematical symbols and letters in algebraic functions. This is more commonly known as dyscalculia (British Dyslexia Association).

Phonological processing

The most commonly associated and researched factor in dyslexia is issues with phonological processing, which is the ability to use sounds to process written and spoken language. People with dyslexia are found to have an impairment with sounding out extended phrases and syllables, therefore struggle to sound out words internally, limiting their speech and their reading comprehension.⁵

Phonological pathway deficits include difficulty in segmenting sounds from words, isolating sounds in words, and changing vocal sounds, resulting in a reduced ability to read unfamiliar words and recognise new sounds. Due to phonological issues dyslexic people have trouble finding rhymes or removing, adding, or changing certain sounds from words.⁵

There is also difficulty in discriminating between similar sounds (words which sound similar such as “flick” and “fleek”). Due to unfamiliarity with sounds, there is also difficulty in tone and rhythm comparison in speech present in dyslexic individuals (Dyslexia UK).

All of these difficulties with sounds and the cognitive processing of the language result in the symptoms associated with dyslexia: reduced reading comprehension, difficulty learning new words, and sensory deficits associated with speech comprehension. Without assistance, the learning ability of dyslexic individuals severely decreases.

Rapid automatised naming (RAN)

Another deficit found in dyslexic individuals is processing speed related to sounds and images (phonological awareness), independent from the actual processing issues.^7,8 This is known as rapid automatised naming (RAN) and is another common factor in dyslexic individuals and sometimes can be a shared symptom with phonological processing, usually resulting in more severe dyslexic symptoms.⁷

Issues with RAN are more commonly associated with reading fluency rather than the phonological processing of words. Phonological processing is associated with accuracy and not indicative of reduced reading speed, with RAN being associated with speed rather than accuracy.^7,8

Dyslexic individuals when tested may be asked to complete RAN tasks, which test a person's ability to name familiar items as fast as possible, assessing processing speed, phonological processing, and executive function. Dyslexic individuals will perform worse and slower than non-dyslexic individuals.⁷

Something to note is poor performance in these tests is also common in other disorders such as ADHD.

Visual processing

On the other side of dyslexia, issues with visual comprehension are also a primary factor.

Dyslexic individuals often have problems with eye movements, such as unstable eye dominance and difficulties with vergence (the ability to focus on objects at varying distances). This can cause symptoms like blurred text, line skipping, and increased reading effort, which reduce both reading ability and processing speed.⁶ Dyslexic individuals reported covering one eye can help with reading due to these effects.⁶

These visual difficulties frequently result in slower reading and the need to reread words and lines. Dyslexic individuals also have an impact on attention spans.¹⁰ Eye movement correlates with attention span, the increased effort required to read decreases because reading requires more effort, which reduces focus. Reduced attention can impair reading ability and is frequently associated with co-occurring conditions such as ADHD.⁶

One theory for visual defects in dyslexia is that dyslexic individuals may have issues with the rapid processing of stimuli due to magnocellular visual pathways (fast visual processing pathways) being abnormal, though this has limited supporting evidence.⁶

Working memory

A person’s ability to process and store information relates to their working memory. There are issues with the processing ability of dyslexic individuals, encompassing verbal, phonological, and visuospatial issues as discussed above.¹¹

A shorter attention span associated with dyslexia can reduce the ability of working memory to process language.¹⁰ This makes it much more difficult to grasp language comprehension at a later age. A reduction in attention span can also prove to have difficulties in planning and completing tasks due to losing focus quicker than usual.¹²

Commonly found in dyslexia is a reduced ability to learn statistical patterns and regularities in text, decreasing learning ability and reading fluency.¹⁴ There also appears to be issues with the prediction of text and speech patterns, with dyslexic individuals relying heavily on short-term memory information rather than long-term. This may be due to the associated symptoms of language breakdown and dysfunctional pathways.^6,13

Whether issues with the pathways cause dysfunction resulting in symptoms, or if dysfunction of pathways arises due to the symptoms is a debated topic with no clear answer.

Assistive methods and technology

First, if a child has been diagnosed with dyslexia at a young age, helping them to improve their reading skills from sound pronunciation to reading speed has proven useful in diminishing the effects of dyslexia into adulthood. While it cannot rid the effects themselves, learning strategies and simply reading more often can help with learning later on and improve the likelihood of academic performance.³

These training exercises can continue on throughout life to assist and train patients. Training can help with task management and keep people's lives productive.

There are many assistive methods to help dyslexic people manage their disorder (AbilityNet):

• A common and easy-to-implement strategy is changing the text font to an accessible font, making it easier to read and type. These fonts to a dyslexic brain can appear more legible and less jumbled, blurry, and squashed. Increasing the font is also a common strategy to make letters and words more obvious and less mixed.
• Changing the colour of the font and the page also assists with reading ability, reducing screen glare.
• Text-to-speech programs and screen readers help them hear the words rather than have to sound them out themselves. This is also very helpful to those who have visual issues and reduced attention spans with reading.
• Whereas, speech-to-text technology helps with reduced writing capabilities and can store conversations/lectures for later use, helping with memory issues and improving learning.
• Mind-mapping software has also proven to be useful as a method to assist with dyslexia, allowing a bit of mess to jot down ideas and thoughts which can then be looked back at. This helps with working memory issues and is a useful tool for managing in an academic or professional environment.

Summary

The reduction in written language fluency found in dyslexia is due to issues with various cognitive symptoms that result in a reduction in processing ability and speed. Each dyslexic individual has a distinct set of symptoms and severity, but subgroups of shared symptoms can be identified.

Working memory issues involved in information processing found in dyslexia include phonological and visuospatial defects. These defects have differing effects on the ability to read and affect different aspects of language, such as piecing the words together, or increased strain when reading.

Access to reasonable adjustments to assist dyslexic individuals is key to their development in language and learning. Dyslexic individuals are not worse at learning but cannot learn quickly or effectively through written words.