Research Projects Funded by IDA Magnetic Resonance Imaging on Cross-Modal Processing in Dyslexia The ability to judge whether sights and sounds happen at the same time is crucial, as it allows us to learn which events in the visual world are associated with which sounds. Our research project was designed to test the hypothesis that children with dyslexia have subtle problems in detecting when two events happen at the same time. Because reading requires that children learn which sounds go with which letters, such difficulties could pose a problem when the child is learning to read. We first developed a task that we could use to test whether dyslexic children had such problems. In the task, the child was shown a flash of light on a computer screen and was also played a sound through headphones. Across different trials, we varied the timing of the light and sound; in some cases the light came first and in others the sound came first, whereas on other trials both appeared at the same time. On each trial we asked the child to simply decide whether the two things happened at the same time or different times, and we used these responses to determine how much time needed to elapse between presentation of the two events in order for the child to decide that they happened at different times. We found that dyslexic children, compared to normal-reading children, needed slightly more time to elapse between sounds in order to decide that they happened at different times. We then used functional magnetic resonance imaging (fMRI) to determine which parts of the brain were active when children make these kinds of decisions. Our preliminary results suggest that normal-reading children exhibit more activity in the right hemisphere of the brain than do dyslexic children during this task. These results suggest that there are differences in how the brain processes information about the timing of visual and auditory events in dyslexic children.
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