Project Summary The capacity to comprehend language lies at the core of a person's ability to gain information from the environment, perform everyday tasks, and maintain normal social relations. The critical role of the left cerebral hemisphere (LH) in supporting these processes has served as a paradigmatic example of neural specialization for higher cognitive functions. However, it is increasingly apparent that the right hemisphere (RH) also makes important, distinctive contributions to language comprehension. The aim of the proposed research is to delineate how processing resources distributed across the two cerebral hemispheres come together in real time to mediate language comprehension and afford memory for verbal material and how these processes and their underlying mechanisms change over the course of normal aging and in response to task demands. The proposal builds on a theoretical framework, based on neuropsychological, behavioral, and event-related brain potential (ERP) studies of language asymmetry, which asserts that LH and RH language comprehension differ because comprehension is cognitively and neurally integrated with language production only in the LH. Nineteen proposed experiments, conducted with both young and older adults, use event-related brain potentials (ERPs), often in combination with visual half-field presentation techniques to preferentially stimulate one hemisphere, to test the hypotheses that (1) the influence of predictive mechanisms increases with more preparation time and changes both the nature and amount of perceptual and semantic information that is gathered from incoming stimuli, (2) such prediction-driven differences in stimulus processing have important downstream consequences for both implicit and explicit memory, and (3) people differentially recruit language processing mechanisms depending on the perceived predictability and importance of the material, affecting comprehension and later memory. These experiments lay the foundation for an understanding of the computational and neurobiological roots of the complex and critical cognitive skill that is language and offer the promise to inform strategies for optimizing the comprehensibility and retention of verbal material – such as important health-related information.