The Neural Basis for Reducing the Risk of Ambiguity in Sentence Processing

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DESCRIPTION (provided by applicant): In daily conversation individuals regularly encounter ambiguous words. For example, "pitcher" could refer to a baseball player or a water container. However, it is not clear how speakers choose words to minimize ambiguities (e.g., saying "baseball player instead of "pitcher"). It also is not clear how listeners choose to interpret an ambiguous word when they are encountered in conversation. One account for minimizing ambiguity during conversation is lexically-based: a linguistic mechanism detects that two conceptual representations share a single word-form representation. We hypothesize the lexical account will be supported by middle temporal cortex, a region often implicated for conceptual and word-form representation. An alternative account is based on neuroeconomics: individuals choose the word with the highest expected individual utility. In this context utility refers to the balance between the risks associated with producing or comprehending an ambiguity and the resources required for producing each term. We hypothesize that the neuroeconomic account will be additionally supported by ventromedial prefrontal (vmPFC) and inferior parietal (IP) cortices, which are often implicated for decision-making processes. The overall aim of this project is to investigate the cognitive and neural basis for minimizing ambiguity in sentence processing. Specific Aim 1 will investigate neurodegenerative disease patients' abilities to minimize ambiguity during sentence production. We will focus on semantic dementia who have middle temporal cortex disease, corticobasal degeneration who have IP disease, and frontotemporal dementia patients who have vmPFC disease. Specific Aim 2 will obtain converging evidence on the neural basis for minimizing ambiguity during sentence production using fMRI studies of healthy subjects. We predict that middle temporal, IP, and vmPFC will all contribute to minimizing ambiguity. Specific Aim 3 will investigate whether minimizing ambiguity is supported by a similar neurological network during both sentence production and sentence comprehension. Understanding the cognitive and neural basis of minimizing ambiguity in sentence processing will improve patient-caregiver communication and yield an improved quality of life, care, and safety for patients. It will also contribute to our understanding of the neural basis for a crucial, but elusive, property of human cognition.