Auditory sensory memory disorder in dyslexic adults as indexed by the mismatch negativity.

Deficient temporal discrimination and vulnerability to masking effects caused by rapidly succeeding or simultaneous sounds might be one factor underlying the phonological difficulties in dyslexia. We evaluated cortical auditory discrimination in dyslexia by recording the mismatch negativity (MMN) for a simple pitch change, for an order reversal of tone pairs, and for tone-pair order reversals, with a third tone either preceding or following the tone pairs. It was found that when an additional tone followed the pairs the MMN amplitude was attenuated, suggesting elevated backward-masking effects in the auditory cortex of dyslexic individuals. In addition, the MMN elicited by pitch change was diminished over the left hemisphere of the dyslexic individuals suggesting left hemisphere auditory dysfunction. These results suggest impaired cortical discrimination of sounds and lowered tolerance for the masking effects of rapidly following sounds in dyslexia.

Plastic neural changes and reading improvement caused by audiovisual training in reading-impaired children.

This study aimed at determining whether audiovisual training without linguistic material has a remediating effect on reading skills and central auditory processing in dyslexic children. It was found that this training resulted in plastic changes in the auditory cortex, indexed by enhanced electrophysiological mismatch negativity and faster reaction times to sound changes. Importantly, these changes were accompanied by improvement in reading skills. The results indicate that reading difficulties can be ameliorated by special training programs and, further, that the training effects can be observed in brain activity. Moreover, the fact that the present training effects were obtained by using a program including no linguistic material indicates that dyslexia is at least partly based on a general auditory perceptual deficit.