Hemispheric contributions to semantic processing in adult dyslexic readers: A divided visual field semantic priming and ERP study

The reported study employed a divided visual field priming paradigm and event-related potential (ERP) to investigate hemispheric contributions to semantic processing in adult dyslexic readers. Twenty-six nonimpaired and 24 dyslexic readers were asked to decide if a target word, which was unilaterally presented, was unrelated or related to the preceding centrally presented prime word. The behavioral results revealed no accuracy difference between the groups for the unrelated words. However, related words produced higher accuracy in the nonimpaired group compared to the dyslexic readers. In addition, the nonimpaired readers had overall shorter reaction time than the dyslexic readers. Moreover, the N400 results showed that while the nonimpaired readers had no differences between the related and unrelated pairs over the left hemisphere (LH), the dyslexic readers showed a more negative response for the unrelated compared to the related pairs. Over the right hemisphere (RH), unrelated pairs produced more negativity than related pairs for both nonimpaired and dyslexic readers. In addition, while the unrelated words produced no lateralization effects, related words produced more negativity over the LH than the RH in the nonimpaired readers group, while no differences between the hemispheres were found in the dyslexic readers. The P600 results revealed that the nonimpaired readers produced overall more positive response over the lateral sites compared to the dyslexic readers. The behavioral and ERP findings suggest differences in semantic processing and hemispheric modulation in adult dyslexic readers relative to nonimpaired readers.