COGNITIVE/LINGUISTIC FACTORS IN ACQUIRED DYSLEXIA

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A program of research is proposed on the topic of reading disorders that occur in premorbidly-literate adults who have suffered focal brain damage. These disorders (acquired dyslexias) frequently accompany other language symptoms (aphasia), but sometimes occur as isolated deficits. Acquired dyslexias are common sequelae of left hemisphere cortical insult from cerebrovascular accident and traumatic head injury. The symptoms exhibited by individual dyslexic patients are interpreted as resulting from deficits to specific processing components within a model of normal reading. Information about the functional sub-systems that are implicated in a particular symptom provide a rational basis to approach two of the long-term goals of the project: the localization in the brain of the cognitive processes involved in reading and the development of treatment techniques for addressing specific symptoms. The project is focused on that aspect of the reading system that is required to "sound out" (or assemble) sound segments (phonology) from print. The inability to perform this operation has been described in several types of patients with deficits to each of these three have been reported. Evidence is reviewed here that these three sub-components of the phonological assembly operation require intact cognitive/linguistic abilities in domains that are not specific to reading: 1) in the processes required to analyze and manipulate sub-lexical phonological segments; and 2) in phonological short-term (working) memory. Three methods are proposed to test the separability of the three hypothesized components and these cognitive/linguistic processes, and to investigate the processing links between them. 1. A battery of tasks addressing each of the hypothesized components and related processes has been developed and will be administered to patients with acquired dyslexia, using the traditional method of testing for dissociations among symptoms: 2. A series of "intervention" studies is planned to investigate the causal direction of co-occurrence relationships by bringing about a change in one hypothesized component and observing its effect on the patient's symptoms: and hypothesized component and observing its effect on the patient's symptoms: and 3> A large-scale connectionist computer model of print-to-sound transformation, developed earlier, will be further refined with the specific goal of determining the optimal size of the sub-lexical unit that participates in print-to-sound mapping.