What is dyslexia? An interview with neuroscientist Guinevere Eden

Guinevere Eden: The last 15 years or so in neuroscience research have uncovered this really interesting idea about how our brain learns to read. Reading is not a natural skill. We use brain areas that have properties that make them suitable to be involved in reading, but they weren't actually designed to do that. What they were designed to do is object recognition.

Eden: Yes. When children learn to read, sometimes they reverse letters that look similar, like "b" and "d." That's because our visual system has a property to make sure that when we see a mirror image of an object we still know it's the same object. When I see a chair that's oriented one way and I see it again when it's oriented slightly differently, I don't go, "What's that object?" I know it's the same object. Our visual system has to be flexible otherwise we're going to have infinite numbers of objects to recognize. So, a kindergartener will think "b" and "d" are the same letter. We have to teach them that they're not the same objects. And the child has to override that particular property of the visual system that was designed to make us good at object recognition.

When we learn to read we also use the oral language structures of the brain, and we blend that with the object recognition pathway. When children see words for the first time, they go through them very carefully and try to match the sounds to the letters. But once most people have done that a few times the word moves to this visual pathway where it's treated more like an object; you recognize the word by sight. As a skilled reader, you don't have to sound out words unless you come across a word you've never seen before, perhaps when you go to university and encounter new vocabulary. That's when you're sounding out words again.

Eden: There are certain skills that if you have them, make you more successful at learning to read. One of them is phonemic awareness. That's basically having an understanding of how words are made up of sounds. People with dyslexia don't have good phonemic awareness. The process of decoding is very hard for them and the difficulty largely stems from understanding how words are broken up into sounds.

Eden: Take the word "cat" or "bat." Those words are made up of three sounds. And those three sounds happen to be represented by three letters. People with dyslexia have a hard time understanding that. If every time you see a word you struggle again and again with how the sounds and the letters correspond, it's difficult to move to that next stage of reading that's more automatic where you recognize words by sight. And so, it becomes very hard to grow your sight word vocabulary that allows you to recognize a word quickly, move on, read fluently, and derive meaning from the words and the sentence that you're reading. If every word is an obstacle and you have to decode it in a very laborious way, it's hard at the end of the sentence to know what the sentence was about. When it comes to describing children with dyslexia you have to remember they are like other children in all other areas, but they have a very isolated difficulty when it comes to learning to read.

Eden: Dyslexia runs in families. If one parent has dyslexia there's about a 40 percent chance their child will have dyslexia. We now know it's not due to one gene but to many genes. It's multi-genetic and that means there are a number of things that can happen to bring about dyslexia. When scientists do studies on the brains of people with dyslexia we find underactivity in the part of the visual system that helps people recognize words by sight and we see underactivity in the areas that help people sound out words.

Now what exactly is happening, we don't know yet. Getting back to the "b" and "d" example. Mixing up letters is not what dyslexia is, but people with dyslexia do often mix up letters. Why? They are manifesting what is a typical profile for a beginning reader. In other words, people with dyslexia are beginning readers for much longer than most readers.

Eden: That's one of the questions that people have been asking for a long time. We can think of the question in several ways. First of all, perhaps whatever caused or interfered with their reading process may have some beneficial effect in another area of the brain. Or it could be that because they haven't read as much, their brain hasn't changed as much. Remember, when people learn to read they are taking over areas of the brain that were not intended for reading. Reading changes the brain and those brain changes may have some deleterious effect. Because of not reading as much, people with dyslexia may be protected from those effects. Those are all really interesting questions that people in science are grappling with.

Eden: I don't think you'd want to go that far. Learning to read cannot be underestimated in terms of our need for it in today's world. But I think it's really important to recognize that children with dyslexia have to become aware of their strengths and weaknesses at a much earlier age. It's tough, but I think it's also a good thing because as they go through life they begin to understand, "I may not be great at reading but I'm good at this other thing. Let's try and do more of this." I think children don't often have to think about themselves in those ways. Kids with dyslexia might then be advancing or making use of another skill, training that skill more, which means they get really good at that skill, better than their non-dyslexic peers.

Eden: That's right. It's an issue of how we adapt to our environment and what's important to be able to do. Right now, it's important for everybody to be a skilled reader so they can succeed at school. But at another time or in another life other things are more important — that you run really fast or that you're very strong. Reading is like any other skill. You might be really good at tennis; your husband may be really good at playing the piano. But those aren't skills that get you through elementary school or into university. They're not the gateway to knowledge the way learning to read is. We all have to get good at reading because it's how we acquire knowledge.

Eden: From an evolutionary perspective, we haven't been reading for very long. We've had oral language for hundreds of thousands of years, but written language was invented somewhere between four and six thousand years ago. For a long time, it was a very small sliver of society that was reading, like the monks and so on were taught to read. Before reading became important to our society you wouldn't know who had dyslexia and who didn't because it never became an issue. But now, of course, reading is something we want everybody to be able to do because reading is so powerful as a tool to acquire knowledge. One of the questions that often comes up is, what's it going to look like in the future? Because we're getting our information in very different ways now. What role will print play in a thousand, 2000, 3000 years? We just don't know.