When a child learns to read he/she needs to learn to correctly combine text and corresponding speech sounds (e.g. the letter ‘a’ and the speech sound /a/). Scientific studies have shown that it may exactly be this combination of text and sound that is difficult for children with dyslexia and leads to their reading problems. In project Leeswinst we want to understand why this is the case and how brain responses to letters and speech sounds change when children with and without dyslexia improve their reading skills over time. A group of seventy 8-10 year old children visited our MBIC lab to perform an ‘aba’ ‘ada’ task on the computer and in the MRI scanner. In the ‘aba’ ‘ada’ task, the children hear an ambiguous speech sound that is sometimes perceived as /aba/ and sometimes as /ada/. Together with this speech sound they see ‘aba’ or ‘ada’ text on a computer screen. Children’s task performance and brain activity tells us how they combine letters and speech sounds.
The first results of our project surprisingly show a similar performance in children with and without dyslexia, apparently indicating a similar coupling of the ambiguous sound and ‘aba’ or ‘ada’ text. However, children’s brain activity as measured in the MRI scanner reveals some interesting differences. Children with dyslexia show significantly less activation in a visual brain area specialized for text (brain area in pink in the picture below) compared to typically reading children. Moreover, regardless of dyslexia diagnosis, this area was less active in children with worse reading skills and worse performance on a task with speech sounds. We also observed that children who are slower in combining letters and speech sounds, have less activation in auditory brain areas that are important for creating letter speech sound combinations (brain area in blue in the picture below). Together these results show that individual differences in children’s reading skills relate to the way in which auditory and visual brain areas process speech sounds and letters. The next important question is now whether and how these brain areas changed when the same children came back to our MRI lab one year later and again performed the same ‘aba’ ‘ada’ task. We are looking forward to presenting these follow-up results in the coming months.