What is dyslexia? An interview with neuroscientist Guinevere Eden
Guinevere Eden directs the Center for the Study of Learning at Georgetown University Medical Center. In this interview with APM Reports correspondent Emily Hanford, she explains what scientists are learning about what happens in the brain when a child learns to read — and what's different in the brain of someone with dyslexia.
September 11, 2017
Hard to Read: How American Schools Fail Kids with Dyslexia
0:00 | 00:51:51
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.
Emily Hanford: So, the part of the brain that our ancient ancestors used to see a tree or a lion coming at them — that's the part of the brain we now use to understand letters and words on the page?
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.
Hanford: What's different in the brain of a person with dyslexia?
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.
Hanford: Give an example.
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.