Alexia and related reading disorders.

Peripheral dyslexias are the result of impairment to processes that convert letters on the page into an abstract orthographic representation. Many aspects of these disorders are difficult to understand in depth. Invariably, there is evidence that some type of word-level perception occurs rapidly in many patients with LBL reading or neglect dyslexia, yet apparently contradictory evidence indicates that part of the word has been misperceived or that the letters must be analyzed laboriously for conscious identification to occur. Current theories attempt to synthesize these different aspects of the patients' performance, but their development is at an early stage. Questions remain also about the domain specificity of the perceptual impairment in LBL reading and about the nature of spatial attention and spatial frames in neglect dyslexia and other forms of attentional disorder. Current understanding of central dyslexias has perhaps advanced further. Well-developed computational models exist of these dyslexias, as do plausible experimental techniques for revealing the activity of semantic and non-semantic routes in normal readers. Nevertheless, the difficult issue of domain specificity arises again with respect to some of the mechanisms invoked, and in this regard, central and peripheral dyslexias continue to pose the same challenge.