A comparison of hemispheric asymmetries in speech-related brain potentials of autistic and dysphasic children

In a previous study (G. Dawson, C. Finley, S. Phillips, & L. Galpert, 1986, Child Development, 57, 1440-1453) it was found that measures of hemispheric asymmetry during speech processing were predictive of level of language ability in autistic children. The purpose of the present study was to determine whether a similar relationship between pattern of hemispheric asymmetry and language ability exists for language-impaired children without autism. Ten autistic children (8-13 years), 10 dysphasic children (6-15 years), and 10 normal children (8-13 years) were compared in terms of their patterns of hemispheric asymmetry in the averaged cortical evoked response to a simple speech stimulus, and the relationship between pattern of hemispheric asymmetry and language ability was assessed for each clinical group. It was found that, for both the autistic and dysphasic groups, the majority of subjects showed a reversed direction of hemispheric asymmetry from that characteristic of the normal group. A strong relationship between pattern of asymmetry and level of language ability was found for autistic subjects; autistic subjects with more severe language impairments were more likely to show reversed asymmetry than subjects with less severe language impairments. In contrast, no relationship between language ability and direction of hemispheric asymmetry in the evoked response was found for dysphasic subjects. Separate analyses of right and left hemisphere evoked responses indicated that language ability was related to right hemisphere activity for autistic subjects, and to left hemisphere activity for dysphasic subjects.