Electrophysiologic correlates of semantic classification in autistic and normal children

This study tested the hypothesis that language processing by high-functioning, verbal autistic children is less influenced by global semantic context than that of their normal peers. Behavioral measures of reaction time and error rate were employed to evaluate speed and accuracy in classifying auditorally presented words according to a superordinate category label. In addition, an electrophysiologic index of semantic expectancy, the N4 component of auditory event-related potentials, was used to assess the relative levels of activation of in-category versus out-of-category words. Age and nonverbal IQ matched groups of 8 normal and 8 nonretarded autistic children were studied. The age range for the autistic participants was 7 years 4 months to 10 years 8 months (M = 8 years 10 months) and for the normal participants was 7 years 6 months to 10 years 11 months (M = 9 years 1 month). Participants responded with a finger lift to any word belonging to the animal category. The instruction set and stimulus list composition (i.e., 50% animal words and 50% unrelated nonanimal words) set up an expectancy for animal words. The autistic children were slower in classifying targets as animal words and made more errors than the normal children, but the increase in error rate was not statistically significant. As expected, N4 was larger for the nontargets than for the targets in the normal control group. By contrast, the autistic children showed no difference in N4 amplitude for targets versus nontargets, providing support for the hypothesized failure of the categorical context to set up a selective expectancy for the target words. As in prior studies, the P3 component to the target stimuli was significantly reduced in amplitude in the autistic group. An unexpected finding was an increased latency of the N1 and P2 components of the obligatory auditory evoked potential that was most prominent over the left temporal region.