Dyslexic Sub-Types: an Investigation into the Visual Problems Associated with Dyslexia and the Relationship between Modality Preference and Teaching Approaches

Abstract

The aim of the research was to develop remedial teaching programmes for sub-types of dyslexics, Two factor analytic studies were carried out, in order to empirically define the sub-types. An auditory type was confirmed, but the existence of a visual sub-type was equivocal, To ascertain why 'visual' and 'verbal' variables were collated under a single factor, three series of four experiments each, were undertaken, The first series investigated the skills required for adequate performance on the ITPA test of visual sequential memory, It was found that good and dyslexic readers differed, not in their visual memory capacity but in their ability to transfer visual information into a verbal store, The second series of experiments was designed to assess the causes of letter reversals in dyslexic, retarded, beginning and normal readers, Again, it was found that, unlike the other groups, dyslexics made reversal errors because of difficulties in labelling the graphemes, and not because of visual dysfunctions, The third series of experiments examined the recall strategies of good and dyslexic readers for phonetically irregular words, The results suggested that good readers were more likely to use a more efficient verbal labelling strategy, whereas the dyslexics relied upon visual memory per se, although when given verbal labelling strategies, their performance improved, These three sets of experiments suggest that problems previously assumed to be visual in origin may, instead, be the result of verbal mediation deficits. Because of the equivocality of the visual sub-type, only dyslexics with auditory difficulties were included in the experimental teaching scheme, Therefore, three groups of six auditory dyslexics were taught basic literacy skills by one of three methods, ie, by training: 1. auditory processing skills; 2. visual processing skills; 3. a combination of both. The results indicated that children taught by methods 2 and 3 made most progress, while children taught through the auditory modality made no more progress than a matched control group, The results are explained in terms of inter-modality and verbal mediation problems,