Dyslexia International has come up with a plain language definition of dyslexia, which I'm going to give you now to set the scene. So 'Dyslexia is a neurologically based condition, which is often hereditary, and it results in problems with reading, writing and spelling. And it's usually associated with difficulties in concentration, short-term memory and organization. Dyslexia is not the result of stupidity, it is not caused by poor schooling, poor home background, poor motivation for learning and it does not clinically manifest with poor sight hearing or muscle control although it may occur with these conditions'. And the World Health Organization uses the following definition of dyslexia in two of its publications. 'A disorder manifested by difficulty learning to read, despite conventional instruction, adequate intelligence and sociocultural opportunity. It's dependent upon fundamental cognitive disabilities which are frequently of constitutional origin'. So we're going to unpack this a bit, it's quite a dense definition and I think it's important to place dyslexia within the context of other reading disabilities and difficulties as well. And one really nice way of doing this is actually using the 'simple' view of reading which is a model that was first developed by Gough and Tumner, American researchers in the '80s and '90s. And so this model talks about a two-way matrix of reading, saying that the two key ingredients for reading are the word recognition part and also then the language comprehension part. We've got a figure of this simple view of reading for you now. So you can see from this figure the model actually results in four quadrants where reading ability can fall. And although this is a simplification, it is actually really a useful first kind of first conceptualization of where might the main reading difficulties for a child lie. So, if we look at the quadrants one by one, so a child can have, first of all, they can have good word recognition which is signified by good decoding. And then they can also have good language comprehension. So the children in this quadrant are going to be good readers because they're not going to have problems. We can then have children who have poor word recognition or decoding, but they have average or strong language comprehension. And these children are typically those who are placed in the dyslexic category, and we'll come back to that in a minute. You then have children who can have strong decoding or average decoding and but then they can have poor language comprehension. And this group are not classically defined as dyslexic but they're children who are going to have problems with reading comprehension and labels are starting to be used such as 'poor comprehenders' or (a) 'specific comprehension deficit'. We're not going to focus so much on those children in this course, but when we get to our intervention stages, many of the comprehension strategies we're suggesting for children with dyslexia will also be completely applicable for this group. And then we do have children who have both poor word recognition and poor language comprehension and so these children are most likely to struggle because they really have the double problem. So this a context, so I think it's important to remember that although dyslexia is often conceptualized as a specific problem with decoding, that can also very much exist with accompanying language problems and it also if we think about things developmentally, the decoding problems can over time actually have an impact on language development itself. This is sometimes called the 'Matthew effect' which you may have heard of. This refers to a biblical reference actually, but the concept is common across reading. And the story here is that if a child has struggles to decode, they're going to perhaps read less text over time, be exposed to less new vocabulary and that gradual reduction of their vocabulary learning can actually result in a lower ultimate vocabulary level compared to their peers. So while their language might have started off at the level of their peers, if they're not being exposed to enough print content, that can be an issue. So those are the main reading difficulties that we see, but then a question is well where do these difficulties come from? Why do children have these problems in the first place? It's a complex issue which we don't fully understand yet. We can think about it at different levels. So, if we go back to our children who are particularly struggling with decoding, it's really the common conceptualization for alphabetic languages right now is that these children have a fundamental problem with something called phonological processing. We've talked a bit about phonology in some of the previous segments: so this is a problem with manipulating the sounds in words and we think that it either causes a problem in storing the correct sound patterns of words, or perhaps the storage is okay, but actually using those sounds in reading or writing is impacted. And this can feel counterintuitive to some people ... dyslexia in the common public perception is often a primarily visually-based issue. And certainly people with dyslexia do report many visual symptoms. But extensive research does suggest that some of the visual factors are more accompanying the primary phonological issue as opposed to being the primary causal factor. So children with dyslexia potentially have this phonological processing deficit. So this is then going to make it hard for them to automatically link sounds and letters when they're trying to decode and then this can have a ripple effect on the rest of reading development. There's also an argument that's quite convincing that there may be a separate factor in turn that's related to speed of processing and this relates to what Vincent was talking about in a previous segment related to problems with automaticity. It seems there might be a separate difficulty with speed of processing, which can exacerbate the phonological processing issues and cause separate issues with acquiring reading fluency. So we could say that the things I've been talking about - this phonological problem and the speed of processing - in a way, we could characterize those as a cognitive level explanation of dyslexia. So, we have the behaviors we see on the surface, the struggle with spelling, the effort with decoding, potentially accompanying verbal short-term memory issues, fluency issues. We then have this next layer of the cognitive explanation. But then you could ask well where does a phonological deficit come from? What's that? What is it? And so then we really need to get to the biology. And here with still so much we need to understand, but we do now appreciate that there is highly likely (a) strong genetic components to dyslexia. This is definitely not genetics in the sense of very fatalistic: if you have the gene you're doomed to have multiple problems. What we're actually learning about the genetics behind learning difficulties is that it's not like the inheritance of hair color, where you either have blonde hair or black hair, and there's kind of a pattern of dominant inheritance. What we are seeing with learning disabilities is the risk alleles are actually ... found on multiple chromosomes and there's actually multiple genes that are going to be contributing towards your ultimate risk. So it's going to be on a continuum; it's not going to be a cut and dry you have dyslexia, you don't. We're going to see a continuum of severity and we're still fully understanding what these genes, how they express themselves, and how they create the risk. But we do know that the risk is genetic risk and somehow then those genes are impacting the cortical development, even when children are In the womb. And so this is affecting very early development, and causing down stream affects. And at this point I'd love to mention one of my favorite research studies; this is where I get a bit nerdy. There's a study done by a great research group in Finland, led by Heikki Lyytinen and in this study they followed children who were at genetic risk of dyslexia. So their parents had dyslexia, they found these children and even in the first week of life they did neuro-recordings from the children's scalps while they were asleep and listening to Finnish speech sounds. And what they found was that the neural responses to those Finnish speech syllables were able to predict when they followed the children through in subsequent years they were able to find that the neural signal was predicting vocabulary development at age four, and reading development, in later, years as well. So, dyslexia is not something that really turns on and is non-existent before a child learns to read. The risk factors are already there in early development and that's why early intervention is going to be so critically important. And we don't fully understand how best we can optimally work in those early years yet. But we do have certain ideas and we will be talking about these in the future weeks as well. But this does mean that there can be early signs of reading difficulties before children are learning to read. Again, we'll talk about this more in future weeks. But it can be seen that as well as, the genetic vulnerability children who are late talkers can often then go on to have reading difficulties, although not always the case, it's important to say.
