The phonologic-deep dyslexia continuum and its relation to concomitant speech and language symptoms in aphasia

Individuals with aphasia demonstrate a wide range of reading and writing deficits, including impaired letter and word recognition, difficulty repeating words and text, difficulty reading aloud, poor reading comprehension, and spelling impairments (Basso, 2003; Roth & Worthington, 2005). One theory used to explain the nature of reading and writing impairments in aphasia is based on a “modularity assumption,” where domain-specific modules make up complex cognitive functions including language processing (Basso, 2003, p. 108). Depending on which modules of this system are impaired due to brain injury, and which modules are functioning, patients with aphasia will have different impairments of their reading and writing skills, often leading to a specific type of dyslexia (Beeson, Maglorire, & Robey, R., 2005; Cherney, 2005; Whitworth, et al., 2005). Damage to the non-lexical route results in “phonological dyslexia” in which case individuals cannot perform grapheme to phoneme conversion and thus must rely on whole word recognition to access meaning. The hallmark of phonological dyslexia is that reading of non-words is significantly more impaired than real word reading. Individuals who suffer from “deep dyslexia” have a disruption not only in the non-lexical route but also in the lexical route, and therefore cannot use whole word recognition to access meaning. Deep dyslexia is characterized by semantic errors, substitution of visually similar words for target words, and difficulty reading function words compared to nouns and verbs (Coltheart et al., 1980, Basso, 2003; Brookshire, 2007)