What is dyslexia? What causes it?

Posted on by rwwiley

 

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).

 

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An illustration of the core phonological deficit in the brains of dyslexic children (Ramus, 2014; accessed from here on July 30, 2019). In yellow are the parts of the brain (left superior temporal lobe) sensitive to phonology in both dyslexic and typical readers; in the green circle is the part of the brain (left inferior frontal lobe) known as Broca’s area, a key area for higher-level processing of speech. A leading theory maintains that it is the connection between these two areas that is primarily responsible for dyslexia, and that genetic factors determine the strength of this connection.

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.

Writing or Reading Letters Backwards Is Not a Sign of Dyslexia

Posted on by rwwiley

Perhaps one of the most persistent misunderstandings of dyslexia is that one of its symptoms is perceiving letters as jumbled—especially as mirror-reversed, making letters like b/d and p/q especially challenging. However, the truth is that this is a very common thing for children to do when learning to read and write. With respect to dyslexia, its most common causes are unrelated to this mirror-reversal effect, or indeed to any difficulties with perceiving or producing single letters.

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The Roman alphabet is full of shapes that represent a different letter when reversed or rotated. This is a relatively unique property of our alphabet—most writing systems around the world have few shapes that are easily confused in this way, if any at all. Rates of dyslexia are high in English, especially compared to languages written in other scripts, but this has nothing to do with the shapes of the letters.

 

So, why do so many children write letters backwards? For adults for whom reading and writing is automatic and effortless, it is understandable that this seems like a funny, obvious mistake. But it turns out that the underyling issue is a difficulty with distinguishing between different perspectives of the same object. In a well-known anecdote illustrating this phenomenon (see Dehaene, 2009), it has been pointed out that  “a tiger is equally threatening when seen or left or right profile” (Rollenhagen & Olson, 2000)—meaning, it’s often helpful to immediately recognize something regardless of which direction it is facing! Thus, the theory is that vision has evolved so that, by default, we perceive shapes like b and d or as the same object. This surely is beneficial in most circumstances, with letters being a notable exception (challenge: can you even think of other shapes or objects that have different names depending on whether they are facing left or right?).

 

Maybe one of the most interesting aspects of this is evidence suggesting that learning to read and write a language like English helps us learn to tell apart left and right. For example, illterate adults are slower to detect a visual difference between shapes like p versus q, as are fluent readers of languages that do not have such shapes that are reversals of each other (see Pegado et al., 2014; Kolinsky & Fernandes, 2014; Danziger & Pederson, 1998).

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In a recently conducted study (Wiley, 2018), even adults (perfectly literate in English) produced mirror-reversed shapes when being taught letters of the Arabic alphabet. In red are the correct orientations for the letters.

 

If you notice a child writing letters backwards, the good news is that this is common—in fact, most children will experience this a stage while becoming literate, and will cease to make such mistakes by around age 11. Of course, this leaves open the question of what are signs of dyslexia, and what might be its underlying cause or causes–you can read more about that here.