PROJECT SUMMARY/ABSTRACT. Children?s ability to reflect upon and monitor their subjective feelings of uncertainty, i.e., engage in uncertainty monitoring, is important for both cognitive and social development. Uncertainty monitoring is a necessary skill for optimal self-guided learning and strategic decision making, and it promotes children?s information seeking behavior and general curiosity about the world. Recent research has revealed that this ability is present even during the preschool-years, is associated with children?s learning and decisions, and even predicts longitudinal improvements in IQ. However, despite the importance of the emergence of uncertainty monitoring during the preschool years, little is known about the neurocognitive mechanisms underlying this ability. The proposed project will address this gap in the literature while providing an opportunity for training in the use of ERP methods, experimental design, repeated measures, as well as intervention methods utilized in developmental cognitive neuroscience research. For Aim 1, we will investigate two ERP components, the N2 and ERN, which have been identified as indicators of conflict detection and error monitoring in executive functioning tasks. We propose to test alternative hypotheses predicting these ERP components will also be associated with 4- and 5-year-old?s uncertainty monitoring ability. Children?s N2 and ERN will be measured using a novel ERP picture identification task which has reduced demand on executive functioning but provides children opportunities to rate their response uncertainty. For Aim 2, we will investigate whether different types of linguistic input promote 3-year-old children?s emerging ability to engage in uncertainty monitoring. This will provide the additional opportunity for training in clinical trials design per NIH designation. We predict that linguistic input that highlights the conceptual boundaries of certainty and uncertainty will improve 3-year-old children?s uncertainty monitoring, whereas linguistic input, which exposes children to other types of mental states language, or an active control which has children practice their rudimentary math skills will not affect uncertainty monitoring. Children will receive the different types of linguistic input using several custom illustrated storybooks, which were created for this study. Results from the studies from Aim 1 and for Aim 2 will both provide substantial contributions to theories of metacognitive development in typically and atypically developing children, and will have the potential to provide insight into future intervention efforts in both educational and social domains.