Dyslexia : Auditory or Phonologic Deficit ?
Maria Mody

A firmly established correlate of reading disability is a deficiency in phonological processing skills. So, for example, poor readers are significantly worse than normal readers on tasks involving phonemic discrimination, manipulation of phones within words, lexical retrieval and verbal short-term memory. Research over the years have implicated the role of speech perception as a source of ramifying deficit. However, the nature and origin of the perceptual deficit has been the centre of debate for over fifteen years. According to the general auditory hypothesis the problem in speech perception lies in the neural transform from acoustic signal to an auditory representation (Tallal, Miller & Fitch, 1993). Dyslexics are believed to have difficulty processing brief and rapidly changing acoustic information occurring in formant transitions that are known to characterize the speech stream. However, a recent study (Mody, Studdert-kennedy & Brady, 1997) failed to demonstrate equivalent deficits in perceiving both speech and acoustically-matched complex nonspeech controls in poor readers, as would be predicted by the auditory-based hypothesis. In fact, the results support the speech-specific hypothesis which claims that poor readers’ perceptual difficulties stem from their weak phonological coding of phonetic distinctions making for ill defined representations in working memory. Implications of these findings for reading remediation will be discussed.