Semantic discrimination in nonspeaking youngsters with moderate or severe retardation: electrophysiological correlates.

Recent studies have used auditory evoked response (AER) procedures to study word meaning in young infants. The present study represents an initial application of these procedures to nonspeaking subjects with moderate or severe mental retardation. AERs were recorded from electrodes placed on the scalp over frontal, temporal, and parietal regions of the left and right hemispheres. As six symbol-experienced subjects viewed visual-graphic symbols (lexigrams), a series of probe tones were presented to elicit the AERs. Half of the symbols were meaningful to the subjects. AER activity recorded from the left hemisphere frontal and temporal electrode sites discriminated between the meaningful and meaningless symbols. Discriminant function analyses indicated that the wave-forms could be correctly classified in terms of the evoking stimulus with greater than 80% accuracy. These findings support the usefulness of AERs for studying the neurolinguistic processes underlying behavioral measures of language performance of difficult-to-assess populations.