The consequences of progressive phonological impairment for reading aloud

The 'primary systems' view of reading disorders proposes that there are no neural regions devoted exclusively to reading, and therefore that acquired dyslexias should reliably co-occur with deficits in more general underlying capacities. This perspective predicted that surface dyslexia, a selective deficit in reading aloud 'exception' words (those with atypical spelling-sound characteristics), should be a consistent feature of semantic dementia, a progressive disorder of conceptual knowledge, and just such a pattern has been observed in previous research. In a similar vein, one might expect the gradual deterioration of phonological processing seen in the nonfluent forms of progressive aphasia to be accompanied by phonological dyslexia, a selective deficit in reading of unfamiliar letter strings, i.e., nonwords. The present study, reporting a case-series consideration of reading-aloud data from 16 progressive nonfluent aphasic patients, revealed a pattern in which both low-frequency exception word and nonword reading were comparably compromised. The severity of the reading disorder was predicted by scores on the expressive language task of picture naming but not the receptive task of spoken word-to-picture matching. Our hypothesis that a phonological deficit underpins diminished performance for both naming and reading was supported by the finding that reading-aloud performance was predicted specifically by the rate of phonological errors in picture naming. Moreover, the strength of this relationship was similar for low-frequency exception words and nonwords, suggesting that reading deficits for these two types of items in this disorder shared a common cause: a progressive impairment of phonological processing.