Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Neuroscience

Supervisor

Johnsrude, Ingrid

Abstract

The auditory system is highly integrative, with feedforward and feedback connections from periphery to cortex (and stages in between). In order to understand how the different levels of the human auditory system interact, it is necessary to simultaneously measure responses from multiple auditory levels. A novel stimulus was paired with electroencephalography (EEG) in 29 young, normal-hearing participants (17-34 years) to examine interactions among stages of the auditory pathway. Temporal regularity was manipulated by continuously accelerating and decelerating the rate of a click-train stimulus (i.e., ~3.5 Hz frequency modulation of the click rate). Adaptation of the brainstem (cochlear nucleus and inferior colliculus) response latencies was observed simultaneously with cortical phase-locking and sustained low frequency activity to the temporal regularity. However, no correlations were found between subcortical adaptation and cortical regularity responses, suggesting that these phenomena may be independent of one another.

Summary for Lay Audience

The present study investigates the relationship between responses from multiple levels of the human auditory system. Specifically, we investigate how processing of temporal, or timing-related, information is related in different auditory levels. Investigating the relationship between temporal processing in the different levels of the auditory system may be useful in understanding complex hearing impairments that are not detectable through standard clinical tests. The most common of these impairments is difficulty hearing speech in the presence of background noise. Using a unique stimulus capable of eliciting responses from multiple levels of the auditory system, and a technique capable of non-invasively recording electrical activity from the brain, we were able to observe temporal processing responses from subcortical and cortical auditory areas simultaneously and non-invasively. We did not find any relationship between processing in these areas, suggesting that temporal processing in the subcortical and cortical levels of the auditory system may be at least partially independent.

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