Date of Award

2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Neuroscience

First Advisor

Murray Grossman

Abstract

Throughout our daily experience, humans make nearly constant use of semantic knowledge. Over the last 20-30 years, the majority of work on the neural basis of semantic memory has examined the representation of semantic categories (e.g., animate versus inanimate). However, a defining aspect of human cognition is the ability to integrate this stored semantic information to form complex combinations of concepts. For example, humans can comprehend “plaid” and “jacket” as separate concepts, but can also effortlessly integrate this information to create the idea of a “plaid jacket.” This process is essential to human cognition, but little work has examined the neural regions that underlie conceptual combination. Many models of semantic memory have proposed that convergence zones, or neural hubs, help to integrate the semantic features of word meaning to form coherent representations from stored semantic knowledge. However, few studies have specifically examined the integrative semantic functions that these high-level hub regions carry out. This thesis presents three experiments that examine lexical-semantic combinatorial processing (as in the “plaid jacket” example above): 1) a study in healthy adults using fMRI, 2) a study in healthy adults using brain stimulation, and 3) a study examining impairments of lexical-semantic integration in patients with neurodegenerative disease. The fourth and final experiment of this thesis examines semantic aspects of combinatorial codes for visual-object representation. This study identifies neural regions that encode the feature combinations that define an object’s meaning. The findings from these four experiments elucidate specific cortical hubs for semantic-feature integration during language comprehension and visual-object processing, and they advance our understanding of the role of heteromodal brain regions in semantic memory.

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