ABSTRACT
The results suggest that between 13 and 20 months of age there are considerable changes in the organization of language-relevant brain systems that occur both between and within the two hemispheres. Previously (M ills et al., 1993) we suggested the working hypothesis that the N200 and N350 index neural activity elicited by processing meaningful lexical information. The results from this study support this hypothesis. M oreover, we propose that by 200 ms after word onset, ERPs to words whose meanings are com prehended by the child elicit greater negative activity than do ERPs to words whose meanings the child does not com prehend. At 13 to 17 months these ERP differences are distributed broadly over anterior and posterior regions o f both the left and right hemispheres. By 20 months of age these differences are limited to temporal and parietal regions of the left hemisphere. For both age groups, unknown words elicit activity largely over the right hemisphere. However, the right-hemisphere asymmetry is more pronounced at 20 months. Backward words do not elicit N200 or N350 activity in either hem isphere at either age. In addition, the results support the hypothesis that the organization of these systems becomes progressively more specialized with both increasing chronological age and the attainment of new language milestones.
