Central auditory testing and dyslexia.
A group of dyslexic pupils with normal end organ function was studied by a central auditory battery to determine whether a hearing disability existed. The clinical features of dyslexia are presented with emphasis on the psychological developmental and functional disorders associated with this reading problem. The central battery of Willeford was selected as the test medium and the results of the 77 dyslexic students were compared to the normative data. The model proposed by Sparks, et al., is accepted as the mechanism for dichotic audition. Reference is made to the organic basis of reading disorders from lesion in the calcarine area to the angular gyrus. The competing sentence test, binaural fusion, rapidly alternating speech perception, and filtered speech are described in detail and are organic foundation for the study. The authors indentified a high rate of failure in this investigation. Over 50% of the dyslexic students failed two of the four tests, and each of the 77 failed at least one component. The most sensitive tests were binaural fusion and filtered speech with less variation from the norm in the remaining two components. The effect of maturation in central audition was measured in each of the four tests. The data suggest: 1. the scores are lower in the early ages in each test; 2. that rapidly alternating speech and competing sentences approach the normal range albeit somewhat delayed; and 3. that binaural fusion and filtered speech improve in score somewhat but rather moderately and never approach the normal range. Based upon the central auditory data and in conjunction with the anatomical pathways of vision, the authors suggest the site of lesion to be in the temporo-parietal cortex and the association fibers.