Disturbed visual processing contributes to impaired reading in Alzheimer's disease.

The relationship between visual processing dysfunction and oral reading impairment was investigated in 17 patients with probable or possible Alzheimer's disease (AD). When dementia severity was controlled, a significant relationship was found between single word oral reading impairments and difficulties discriminating words written in different fonts and photographs of objects in different orientations, which are all functions believed to be dependent on the integrity of left ventral temporal-occipital visual association regions. By contrast, there was no significant relationship between reading performance and the score on a test of spatial localization, believed to be more dependent on parietal lobe function. There was also no relationship between reading ability and discrimination of unfamiliar faces, a function thought to engage right inferotemporal lobe structures. In contrast to the significant association between impaired reading and certain visual processes, when dementia severity was controlled, there was no relationship between reading and lexical semantic impairment. These results highlight the contribution of visual processing deficits to impaired oral reading in AD and further suggest that this association may derive from neuropathological changes in areas of the left temporal occipital lobes specialized for high-level visual processing.