Deep Alexia

The reading of patients with deep alexia displays all the alexia symptoms of phonological alexia, with the addition of the defining feature of the disorder, the production of semantic paralexias. When semantic paralexias are produced at a rate that is greater than chance, the entire symptom complex is almost guaranteed to be seen: poor pseudoword reading, a part-of-speech effect in which verbs are read more poorly than nouns, and functors are read more poorly than verbs, a concreteness effect, and the production of derivational errors and functor word substitutions. The pseudo-

word reading deficit in deep alexia tends to be more severe than that seen in phonological alexia. Responses may be completely dissimilar to the target pseudoword, or no response at all is produced.

It has been suggested that deep alexia represents the (most impaired) end point of a continuum that includes the various manifestations of phonological alexia. As in phonological alexia, the pronunciation of written words cannot be accessed directly; reading proceeds semantically. However, in deep alexia there is an impairment within the semantic reading route that results in the semantic paralexias. This impairment may be within the semantic processing system or in the ability of that system to access the correct phonological code.

The typical lesion that produces deep alexia is a large one, affecting much of the left frontal lobe and extending into the parietal and temporal lobes as well. It has been posited that the symptom complex of deep alexia is actually a manifestation of right hemipshere reading in the presence of a left hemisphere that is greatly damaged. Support for this notion has come from studies of reading in split-brain patients. It has been demonstrated that the right hemisphere of some of these patients can read concrete words but not abstract words or functors and cannot determine the pronunciation of nonwords (ascertained with a rhyme task). This pattern is similar to the reading pattern of patients with deep alexia.

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