AUDITORY EVENT-RELATED POTENTIALS, DICHOTIC-LISTENING PERFORMANCE ANDHANDEDNESS AS INDEXES OF LATERALIZATION IN DYSLEXIC AND NORMAL READERS

Evidence suggests that children with developmental dyslexia have poor phonological processing skills, are less likely to show lateralised ac tivation during the processing of verbal information than children wit h normal reading ability and tend towards the left of the handedness c ontinuum. The present study investigated this relationship between cer ebral lateralisation and reading ability in children with and without dyslexia, directly using a dichotic listening paradigm with contempora neous recording of auditory evoked potentials and indirectly using mea sures of hand preference and hand skill. The two groups were significa ntly different on a phonemic awareness task, particularly with referen ce to rime rather than phoneme onset. The two groups performed equally well on the dichotic listening task. However, normal readers produced significantly greater N100 amplitudes in the left temporal region dur ing dichotic listening than the dyslexics who displayed approximately equivalent levels of amplitude bilaterally. In terms of hand preferenc e the dyslexics were significantly less right-hand preferent than the controls, although the groups did not differ on a measure of right/lef t hand skill. The AEP lateralisation indices and the hand preference s cores were significantly related to phonemic awareness performance. Th e different patterns of AEP activity produced by the two groups of chi ldren during the dichotic listening task and the differences in hand p reference may be related to abnormal cerebral lateralisation of langua ge functions. The failure of the dichotic listening task to discrimina te between the two groups in spite of evidence of differences in corti cal activation suggests that the processing difficulties which may be indexed by these differences in cortical activation affect the reading process at a later stage than that tapped by dichotic listening.