The neural correlates of object-centered processing in reading: a lesion study of neglect dyslexia.

Neglect dyslexia--a peripheral reading disorder generally associated with left spatial neglect--is characterized by omissions or substitutions of the initial letters of words. Several observations suggest that neglect dyslexia errors are independent of viewer-centered coordinates; the disorder is therefore thought to reflect impairment at the level of object-centered representations. This hypothesis is indirectly supported by lesion studies connecting object-centered neglect errors with damage to posterior cortical regions lying in the ventral visual stream. Here, we performed a lesion-symptom mapping study of 40 patients with spatial neglect asked to read words presented at different positions relative to a viewer-centered coordinate frame. We found that the frequency of object-centered reading errors was constant across horizontal positions, whereas the frequency of entirely neglected words (reflecting a page-centered deficit) linearly increased from right to left. Damage to the intraparietal sulcus and the angular and middle temporal gyri was the best predictor of object-centered errors. We discuss these findings with reference to a role of the posterior parietal lobe in adapting the size of the attentional focus and biasing object representations elaborated in the ventral visual stream.