Doctoral Dissertation Research: Neural Bases of Semantic Composition in the Verb Phrase

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The richness of natural language semantics stems from the ability to compose elements together and to derive novel meanings from these combinations. Understanding this ability has been a central goal in the neurobiology of language, as well as in theoretical linguistics. However, despite a rapidly growing body of research, the brain basis of composition has been vaguely understood at best. Most of the progress during the last decade has been limited to general descriptions of the sentence level, identifying a network of brain areas recruited for the composition of sentential meaning but not further specifying how the individual facets of sentence composition are encoded. Considering the assumption in formal semantics that composition can happen via at least two different rules, understanding very basic instances of composition in various linguistic environments is an essential first step for characterizing the neural basis of sentence interpretation. To this end, this dissertation takes a bottom-up approach, investigating neural substrates of small units of composition, with its focus on English verb phrases. Disentangling the two major modes of composition around a verb, namely modification (e.g., paint + slowly) and saturation of arguments (e,g., paint + a picture), this work aims to provide an answer to the question of how the meaning of a complex event description, e.g., "John reluctantly painted a picture," is composed from the various event elements, i.e., John (agent), reluctantly (manner), painted (action), and a picture (object). This work aims to lay a critical foundation for a computationally detailed characterization of full sentence composition. This dissertation consists of three studies that take advantage of the high spatiotemporal resolution of magnetoencephalography to characterize the dynamics of composition. The first experiment investigates the neural signatures of modification in the verbal domain, asking how the combination of a verb and its modifier engages the brain, and how this overall pattern compares to that of noun-modifier combination, for which stable results have been described in prior work. The second experiment investigates the neural representation of conceptual specificity in the event domain. Previous literature has shown that a particular brain region, the left anterior temporal lobe (LATL), is sensitive to conceptual specificity in the object domain (e.g., boat vs. canoe). Asking whether event specificity also involves the same area in the same way, the second experiment manipulates the conceptual specificity of events (e.g., "hoard fuel" vs "store fuel"). The last experiment explores situations of (possible) semantic composition in which the combining words do not form a syntactic constituent. In all, these studies combine insights from theoretical linguistics and from the psychological literature on concepts and categories to elucidate the neural reflexes of event composition as manifested in verb phrase interpretation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.