Specific reading disability (SRD) is found in over 3% of children in this country. Despite the prevalence o the disability, it is still defined by exclusion since no reliable diagnostic tests for SRD have been found. Part of the reason for this failure is that SRD is a heterogeneous disorder. Deficits in visual and auditory processing, memory impairments and intersensory integration have all been shown to exist in SRD subjects. This project is designed to investigate the role of temporal processing, especially in relation to the visual system, in SRD subjects. Visual evoked potentials will be used to study separate visual pathways which have been implicated in SRD. Previous studies have suggested that when parallel pathways within the visual system are assessed separately, the magnocellular pathway is found to be impaired in SRD subjects, while the parvocellular pathway is unimpaired. The magnocellular pathway is thought to be involved in processing movement and depth and is therefore involved in assessing the location of objects in space. The parvocellular pathway is involved in assessing the form of an object. Impairment of the magnocellular pathway might therefore explain the anecdotal reports of some SRD subjects that letters and words appear to move on the page. The functions of these individual visual pathways will be assessed in SRD adults and children. The results of these studies will be combined with information on specific reading deficits, and with measures of temporal processing in the auditory and motor domains. The investigation is designed to assess whether SRD is a disorder which affects the temporal processing in the visual, auditory and motor domains simultaneously, or whether there are groups of subjects with disorders of only one of these processes. This information could lead to a more precise description of the processes involved in reading disability. This, it is hoped, will result in a more objective diagnosis of the disability, with concurrent implications for better treatment and/or remediation of individual difficulties.
