Dyslexia and cognitive function.

The research undertaken investigates the difficulties that dyslexics have with reading and spelling, attempting to explain these from the standpoint of cognitive psychology, using an information processing paradigm. Evidence is produced to support the contention that dyslexics suffer from both a short-term memory deficit and a specific weakness in accessing deeper levels of processing. This manifests itself as a wider limitation in processing all forms of information. As a basis for research, neurological and psychological perspectives are examined and, from a study of observed symptoms, a classification and definition of dyslexia is offered. The precise differences between dyslexia and general reading retardation are discussed with specific reference to the significance of short-term memory deficits and by an analysis of the theoretical levels of processing. Haber and Hershenson's model of information processing is adopted as the frame of reference for the experimental investigation. This investigation considers the hypothesis that dyslexia is characterized by both a limited capacity in short-term memory, exhibited by reduced channel capacity and a limited access to deeper levels of processing. Three experiments are presented to test this hypothesis: (1) An investigation into the performance of cross-lateral, dyslexic and control groups on a direct recall task using various forms of tachistoscopically presented information. (2) An investigation into immediate recall of auditory signals of varying set size under direct recall conditions by three different age groups of dyslexic and control subjects. (3) An investigation into spatial and temporal factors that influence dyslexic's performance on a memory task.The results show that dyslexic's performance in all these tasks is inferior to that of matched controls. The hypothesis is therefore accepted. A model is presented that incorporates the initial hypothesis and is substantiated by considering current research literature. Finally the implications of these findings for teaching are considered.