Project Summary The proposed research is designed to illuminate how semantic organization emerges in the course of development, and how it contributes to the fundamentally human ability to comprehend language. The proposed research will be guided by two general hypotheses. The first hypothesis is that comprehension may fundamentally rely on semantic organization – an organized network of words. The second hypothesis is that semantic organization emerges from exposure to statistical regularities in language input and from the developing ability to extract these regularities. To test these hypotheses, we will conduct three studies with 4-9- year-old children, and adults. The proposed project has the following Specific Aims. Specific Aim 1 is to conduct a cross-sectional training study (Study 1), presenting 4- to 9-year-old children and adults with controlled, varied exposure to sentences containing novel words that are rich in regularities, and testing how the amount of exposure and the ability to form semantic links affect subsequent comprehension. Specific Aim 2 is to recruit 4-year-old children and use a longitudinal design to examine how exposure to language and maturation of ability to form semantic links affect the development of semantic organization (Study 2). Specific Aim 3 is to use a longitudinal design (with the same sample as Study 2) to examine whether the development of semantic organization drives improvements in language comprehension. The proposed project will advance our understanding of a critical component of typical cognitive and language development and inform theoretically-based enrichment programs for atypical language development.