What is dyslexia? What causes it?

 

Dyslexia is surely one of the most recognized learning disabilities, yet also one of the most commonly misunderstood. One difficulty is simply that the term is used in different ways by different groups: teachers, education specialists, and psychologists will likely all provide different definitions of dyslexia.

 

In common language, ‘dyslexia’ usually refers to difficulties with reading, but very often challenges with spelling are also present (although the term for a problem specifically with spelling is dysgraphia). And unless otherwise specified, dyslexia usually refers to a developmental dyslexia, meaning a reading/spelling deficit appearing in children as they mature. This is opposed to acquired dyslexia, meaning the loss of reading ability after a brain injury, such as a stroke (for more on acquired dyslexia and dysgraphia, read here).

 

There are a lot of myths and misconceptions about dyslexia (do a quick web search for “dyslexia myths” and you’ll find lots of great information debunking them), one of which I’ve written about previously (see here). What it all boils down to is that dyslexia is a difficulty with mapping between the written word and its sound and meaning—but this difficulty can arise in different ways, depending on the individual and the language being read.

 

Dyslexia rates are highest in languages that use what is known as “opaque orthography”, like English, and lowest in languages that have transparent orthography. What’s the difference? English has a very opaque orthography—think of words like “ghost” (what is that ‘h’ doing there?) and “island” (not ice-land or is-land!). Most English letters can be pronounced multiple ways, sometimes even within the same word (the ‘c’s in “circle”). Even worse, most English sounds can be spelled multiple ways (like the vowel sound in “wait”, “late”, and “freight”… for more on why English spelling is so weird, see this post here). Other languages, like Spanish and Italian, have much less complicated relationships between letters and their sounds. So for example, at the end of first grade, children learning to read English make more errors when reading (67% in the United Kingdom) than those learning French (28% in France) or Spanish (8%; Dehaene, 2009).

 

Probably the main reason dyslexia is more diagnosed in English-speaking children is because the “core deficit” of dyslexia is actually one related to phonology: a disability with learning how to map between letters and their sounds (see Ramus, 2014). This means that for most children, the best way to overcome dyslexia will be educational interventions that focus specifically on phonology and how to ‘sound out’ words. Moreover, this seems to be largely genetically determined.  While there may be associated deficits in areas besides phonology, the underlying source of difficulty for these children is in mapping between letters and sounds.

 

However, there are some children whose reading difficulties are not related to phonology, but instead to deficits in memory, attention, or vision (although this issue remains controversial). Only an educator or psychologist with special training can distinguish between different underlying cognitive deficits, as it requires comparing and contrasting performance on carefully chosen tasks. It’s also worth mentioning that for acquired dyslexia, there are clearly defined sub-types, some of which have nothing at all to do with phonology.

 

In summary:

• Dyslexia is a difficulty with relating the written word on the page (or a screen!) to sound and meaning
• Dyslexia in children, known as developmental dyslexia, is primarily (although not exclusively) caused by a deficit in phonology, determined by genetic factors
• Dyslexia is not a sign or symptom of low intelligence; it is not a visual problem with seeing letters correctly or controlling eye movements

 

 

 

Suggested links:https://dyslexiaida.org

References:

•Dehaene, S. (2009). Reading in the brain: The new science of how we read. Penguin.

• Ramus, F. (2014). Neuroimaging sheds new light on the phonological deficit in dyslexia. Trends in Cognitive Sciences, 18(6), 274–275.