Orienting of visual attention in dyslexia: evidence for asymmetric hemispheric control of attention

The control of attentional orienting was studied in children with specific reading disorder (SRD) or dyslexia, and it was compared with that of normal readers. We used the covert orienting paradigm to measure subjects' reacti on times for target detection both in valid and invalid cue conditions, eit her in the left or in the right visual fields. In experiment 1, we investig ated exogenous orienting. The cue consisted of a peripheral abrupt onset an d the cue-target delay was 350 ms. As compared with normal readers, in dysl exics the cue effect was absent in the right visual field, whereas in the l eft visual field a greater cue effect was observed. No visual field asymmet ry was found in normal readers. In experiment 2, we investigated endogenous orienting. The cue was shown centrally and the cue-target delay was 750 In s. In dyslexics and normal readers, orienting of attention was present in b oth visual fields. However, in the invalid condition, dyslexic children sho wed significantly slower reaction times in the left visual field than in th e right visual field. These results were interpreted as being due to an asy mmetric control of visual spatial attention, possibly related with a poster ior attention mechanism deficit in the right parietal cortex and/or an inte rhemispheric dysfunction and/or an impairment of cerebellar functions.