Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Stimulus Temporal Coherence Strongly Influences Rapid Plasticity in Primary Auditory Cortex under Global Attention(2013) Xu, Yanbo; Shamma, Shihab A; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Temporal coherence of stimulus features is a key property of sounds that emanate from single source. Consequently, it is important to understand how it may influence the direction and extent of the rapid plasticity postulated to occur during the streaming of concurrent sounds. We postulated that when animals listen attentively to coherent or incoherent stimuli, responses would adapt to effectively encode the correlational structure of the stimuli. In this study, ferrets were trained to attend globally to two-tone sequences which were played either simultaneously (SYNC) or alternatively (ALT) on a trial-by-trial basis, and to detect a transition to a random cloud of tones by licking a waterspout for reward. Neuronal activities were collected in the primary auditory cortex during performing the task and passively listening to the same stimuli sequences. Compared with the passive condition, neuronal responses changed distinctively between SYNC and ALT trials under the effect of attention. These results provide neuronal evidence for the role of stimulus temporal coherence in modulating responses during attentive listening to complex sounds.Item Auditory Streaming: Behavior, Physiology, and Modeling(2011) Ma, Ling; Shamma, Shihab A; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Auditory streaming is a fundamental aspect of auditory perception. It refers to the ability to parse mixed acoustic events into meaningful streams where each stream is assumed to originate from a separate source. Despite wide interest and increasing scientific investigations over the last decade, the neural mechanisms underlying streaming still remain largely unknown. A simple example of this mystery concerns the streaming of simple tone sequences, and the general assumption that separation along the tonotopic axis is sufficient for stream segregation. However, this dissertation research casts doubt on the validity of this assumption. First, behavioral measures of auditory streaming in ferrets prove that they can be used as an animal model to study auditory streaming. Second, responses from neurons in the primary auditory cortex (A1) of ferrets show that spectral components that are well-separated in frequency produce comparably segregated responses along the tonotopic axis, no matter whether presented synchronously or consecutively, despite the substantial differences in their streaming percepts when measured psychoacoustically in humans. These results argue against the notion that tonotopic separation per se is a sufficient neural correlate of stream segregation. Thirdly, comparing responses during behavior to those during the passive condition, the temporal correlations of spiking activity between neurons belonging to the same stream display an increased correlation, while responses among neurons belonging to different streams become less correlated. Rapid task-related plasticity of neural receptive fields shows a pattern that is consistent with the changes in correlation. Taken together these results indicate that temporal coherence is a plausible neural correlate of auditory streaming. Finally, inspired by the above biological findings, we propose a computational model of auditory scene analysis, which uses temporal coherence as the primary criterion for predicting stream formation. The promising results of this dissertation research significantly advance our understanding of auditory streaming and perception.