Attention helps us process potentially important objects by selectively increasing the activity of sensory neurons that represent the relevant locations and features of our environment. This selection process requires top-down feedback about what is important in our environment. We investigated how parietal cortical output influences neural activity in early sensory areas. Neural recordings were made simultaneously from the posterior parietal cortex and an earlier area in the visual pathway, the medial temporal area, of macaques performing a visual matching task. When the monkey selectively attended to a location, the timing of activities in the two regions became synchronized, with the parietal cortex leading the medial temporal area. Parietal neurons may thus selectively increase activity in earlier sensory areas to enable focused spatial attention.

WE tested the hypothesis that in a cluttered visual scene, the magnocellular (M) pathway is crucial for focusing attention serially on the objects in the field. Since developmental dyslexia is commonly associated with an M pathway deficit, we compared reading impaired children and age-matched normal readers in a search task that required the detection of a target defined by the conjunction of two features, namely form and colour, that are processed by the parvocellular dominated ventral neocortical stream. The dyslexic group's performance was significantly poorer than the controls when there were a large number of distractor items. The scheme of selective attention proposed from these results provides a neural mechanism that underlies reading and explains the pathophysiology of dyslexia.