ERP differences in dyslexia

Young children with dyslexia do not respond as well as their non-disabled peers when asked to determine whether a briefly shown string of letters are the same as another string seen just seconds earlier, according to Urs Maurer (Depar tment of Child and Adolescent Psychiatry, University of Zurich, Switzerland) and colleagues (various institutions). Although their accuracy in detecting target items (matches) increased as their grew from kindergartners to second graders, receiving instruction during that time, children with dyslexia did not improve as much as their peers. In addition, electroencephalography revealed that the children with dyslexia responded significantly more slowly than their peers during the first few milliseconds after the images appeared.

Impaired tuning of a fast occipito-temporal response for print in dyslexic children learning to read

Urs Maurer, Silvia Brem, Kerstin Bucher, Felicitas Kranz, Rosmarie Benz, Hans-Christoph Steinhausen, and Daniel Brandeis

Developmental dyslexia is defined as a disorder of learning to read. It is thus critical to examine the neural processes that impair learning to read during the early phase of reading acquisition, before compensatory mechanisms are adapted by older readers with dyslexia. Using electroencephalography-based event-related imaging, we investigated how tuning of visual activity for print advances in the same children before and after initial reading training in school. The focus was on a fast, coarse form of visual tuning for print, measured as an increase of the occipito-temporal N1 response at 150^270 ms in the event-related potential (ERP) to words compared to symbol strings. The results demonstrate that the initial development of reading skills and visual tuning for print progressed more slowly in those children who became dyslexic than in their control peers. Print-specific tuning in 2nd grade strongly distinguished dyslexic children from controls. It was maximal in the inferior occipito-temporal cortex, left-lateralized in controls, and reduced in dyslexic children. The results suggest that delayed initial visual tuning for print critically contributes to the development of dyslexia.

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