The neuropsychological investigation of dyslexic readers: an experimental approach to subtyping

Abstract

Based on Luria's notion of functional neuronal systems, reading has been hypothesized to require the adequate functioning of both the anterior and posterior cerebrum. Failure to be able to read has been hypothesized to be the result of dysfunction occurring anywhere throughout those functional units. In adults, anterior and posterior language problems have been established by assessing verbal fluency. Nonfluent output has been associated most often with anterior dysfunction, while fluent output has occurred with posterior dysfunction. The primary purpose of the present exploratory study was to evaluate the utility of verbal fluency as a dimension on which to classify children with the language problem of dyslexia. Subjects first were identified as dyslexic readers (DR) or normal readers (NR) based on a statistical formula which determined whether IQ and reading achievement scores were significantly discrepant. A traditional measure of verbal fluency then was used to determine that the DR children were less fluent than NR children. DR children subsequently were classified into nonfluent (NF) and fluent (F) subgroups. Initial validation for die fluency construct then was established by examining children's performance on other language and motor tasks associated with anterior and posterior functioning. As predicted, the DR-NF children performed more poorly or displayed specific deficits on tasks purported to tap anterior functioning (e.g. verbal memory, motor perseveration, and vigilance) while DR-F and NR children did not. A dual processing model was proposed to explain the findings for the DR-NF children. Limitations, implications for the treatment of DR children, and directions for future research are outlined