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Effect of Repeated Exposure and Attention on Stream Segregation of Stimuli at the Fission Boundary

By Dameon Harrell


Neural processes of the auditory system decompose and perceptually organize mix- tures of sound such that we can hear and follow separate auditory streams: the speech of a single person at a party or the melodies of different instruments in an orchestra. Decades of research has yielded much insight into the perceptual dynamics of stream segregation. Yet, some perceptual attributes of stream segregation are not well defined. One example of this is a concept referred to as the fission boundary (FB). The FB is generally con- ceived as a threshold below which stream segregation cannot occur or can only occur with a small probability. Here, I demonstrate that this prior conception of the FB was pri- marily determined by measurement method, as opposed to perceptual limitations of the auditory system, and suggest an alternate definition of the FB. Prior investigations into the neural underpinnings of stream segregation have revealed cortical correlates, but animal models have suggested that stream segregation may be- gin with neural processes in the brainstem. Two recent studies of stream segregation with human participants recorded the frequency-following response (FFR) as a measure of subcortical neural activity. The studies reported inconsistent results: one study provid- ing evidence of an FFR correlate of stream segregation and the other finding no effect of steaming in the FFR. In Experiment 2 of this dissertation, participants performed a stream segregation task while FFRs were recorded simultaneously. The results are consistent with the prior study showing no effects of streaming on the FFR. While the FFR reflects sensory processes and experience dependent long-term plasticity, it may not reflect im- mediate perceptual states associated with stream segregation

Topics: stream segregation, fission boundary, frequency-following response
Publisher: OpenCommons@UConn
Year: 2019
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