Chia-wen Lo successfully defended her dissertation on April 13th – Many many Congratulations Dr. Lo!!!
Title: Testing low-frequency neural oscillations in sentence understanding
Committee:
Jonathan Brennan (chair),
Natasha Abner,
Nai Ding,
Rick Lewis
Abstract:
Human language has the unique characteristic where we can create infinite and novel phrases or sentences; this stems from the ability of composition, which allows us to combine smaller units into bigger meaningful units. Composition involves us following syntactic rules stored in memory and building well-formed structures incrementally. Research has shown that neural circuits can be associated with cognitive faculties such as memory and language and there is evidence indicating where and when the neural indices of the processing of composition are. However, it is not yet clear “how” neural circuits actually implement compositional processes. This dissertation aims to probe “how” composition of meaning is represented by neural circuits by investigating the role of neural oscillations in carrying out composition. Neuroelectric signals were recorded with Electroencephalography (EEG) to examine the functional interpretation of low-frequency neural oscillations in the so-called delta band of 0.5 to 3 Hz. Oscillations in this band have been associated with the processing of syntactic structures (Ding et al. 2016). First, whether these oscillations are indeed associated with hierarchy remains under debate. This dissertation uses a novel condition in which the same words are presented, but their order is changed to remove syntactic structure. Only entrainment with syllables was found in this “reversed” condition, supporting the hypothesis that delta oscillations entrain to abstract syntactic structures. Second, we test the timing for language users to combine words and comprehend sentences. The threshold of timing for achieving successful language comprehension remains unclear and the design of the experiment aims to provide evidence for the debate of oscillation-based account and evoked response account. This dissertation manipulates the length of syllables and regularity between syllables. The results support the oscillation-based account and suggest delta oscillations reflect a top-down processing. Third, what semantic information modulates delta oscillations is unknown. This dissertation examines several semantic variables typically associated with different aspects of semantic processing. The stimuli are created by varying the statistical association between words, world knowledge, and the conceptual results of semantic composition. The current results suggest that low-frequency oscillations are not driven by semantic processing. Based on the above findings, we propose that delta oscillations reflect a top-down predictive processing that involves syntactic information but not semantic information.