Abnormal visual event-related potentials of autistic children.

This study compared the visual ERPs and concurrently measured fixation times of autistic children with those of normal children and two psychiatric control groups (so-called "externalizers" and "internalizers"). Autistic children had, in contrast with normal control groups, smaller P3 waves (occipital maximum) to visual target stimuli but did not differ in this respect from the two psychiatric control groups. When the autistic group was split into "good" and "bad" performers, the latter group had significantly smaller amplitudes than the former. No difference was found between the groups in electrophysiological reactivity to the first, novel stimulus of a habituation series. However, an unexpected change in stimulus location induced an increased Fz N400 in the normal group but not in the autistic group or the two psychiatric control groups. In addition, in a non-task-relevant habituation condition, the autistic group fixated complex visual stimuli for shorter times and had smaller occipital P3 waves than the control groups. Analysis of covariance showed that the smaller P3s could not be explained by the shorter fixation times. In none of the ERP parameters were there differences in habituation rate between the controls and the autistic children.