DYSLEXIA: ACQUIRED
The loss or partial loss of the ability to read as the result of illness, accident or brain surgery. Acquired dyslexia is conventionally divided into peripheral dyslexias, where there is impairment of the system which permits visual analysis, and central dyslexias, where the processing of the signal is affected.
The peripheral dyslexias are:
Attentional dyslexia, where the reader is distracted by adjoining words (or sometimes adjoining letters). GLOVE and SPADE seen together might produce the response glade. There is apparent damage to the reader’s attentional filter, so that they are no longer able to focus on one piece of visual evidence at a time.
Neglect dyslexia, involving a failure to attend to the onsets of words: a reader might interpret GROSS as cross.
Letter-by-letter reading, where words are decoded letter by letter but the letters are given their alphabetic names: BED = Bee-Eee-Dee.
The central dyslexias are:
Surface dyslexia, where patients can read words with regular spellings but regularise those with irregular. One view is that they suffer from impairment of the lexical (whole word) route but continue to use the sub-lexical (letter-by-letter) one.
Phonological dyslexia, where patients can pronounce familiar words, both regular and irregular, but are incapable of suggesting pronunciations for non-words. This suggests an intact lexical route but an impaired sub-lexical one.
Deep dyslexia, where there is disruption not just to the processing of form but also to the processing of meaning. Like phonological dyslexics, deep dyslexics find non-words impossible to read aloud. But they also make semantic errors where the word produced is different in form from the target but similar in meaning (APE read as monkey, ARTISTread as picture). They substitute function words (HIS read as in) and suffixes (BUILDER read as building). They also have a greater success rate with concrete than with abstract nouns. This condition may provide valuable information about the distribution of information in the lexicon. On the other hand, it may represent a loss of reading processes from the left hemisphere and their transfer to the right, which is less adapted to language processing.
Non-semantic reading, where the processing of meaning seems to be affected but not that of form. A patient can read aloud words and non words but has difficulty in attaching meanings to them.
See also: Aphasia, Disorder, Dysgraphia: acquired, Dyslexia: developmental
Further reading: Caplan (1996); Ellis (1993); Harley (2001); Harris and Coltheart (1986)
