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 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 recent 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. Seventeen proposed experiments, using ERPs (often in combination with visual half-field presentation techniques to preferentially stimulate one hemisphere) and eyetracking measures with both young and older adults, test the hypotheses that (1) differences in the efficacy of neural connectivity within each hemisphere and across age set up qualitatively different processing dynamics during language comprehension, (2) these differences in processing dynamics can be modulated by factors such as stimulus predictability, task demands, and control - yielding different functional outcomes and (3) the roots of processing dynamics important for language comprehension can be traced to genetic factors that affect neural circuitry important for hand preference. These experiments lay the foundation for an understanding of the computational and neurobiological roots of the complex and critical cognitive skill that is language.
Language comprehension is a crucial component of human life, and a reduction in language capabilities, as a function of advancing age or with brain damage as from a left hemisphere stroke, has important personal and societal costs. The proposed research examines language comprehension differences across the two cerebral hemispheres and as a function of age in order to understand what factors characterize and promote effective language processing. The long-term goal is to uncover ways to protect against or compensate for age-, trauma-, or disease-related reductions in the ability to comprehend and remember language.
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