Auditory and visual evoked potentials in individuals with organic and cultural-familial mental retardation.

Brainstem, middle-latency, and long-latency auditory evoked potentials (BAEPs, MAEPs, and LAEPs) and visual evoked potentials (VEPs) were recorded from subjects without mental retardation (control subjects) and from subjects with organic mental retardation or cultural-familial mental retardation. Both mentally retarded groups had smaller mean VEP amplitudes and longer mean LAEP latencies in response to target stimuli than did the control subjects, showing that the target stimuli were evaluated more slowly by the subjects with than by those without mental retardation. We found no significant differences between the mentally retarded and control groups with regard to BAEPs or MAEPs, and the two mentally retarded groups did not differ significantly in any EP parameter. The implications of these results for the defect and developmental theories of mental retardation were discussed.