Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item EFFECTS OF AGE ON CONTEXT BENEFIT FOR UNDERSTANDING COCHLEAR-IMPLANT PROCESSED SPEECH(2024) Tinnemore, Anna; Gordon-Salant, Sandra; Goupell, Matthew J; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The number of people over 65 years old in the United States is rapidly growing as the generation known as “Baby Boomers” reaches this milestone. Currently, at least 16 million of these older adults struggle to communicate effectively because of disabling hearing loss. An increasing number of older adults with hearing loss are electing to receive a cochlear implant (CI) to partially restore their ability to communicate effectively. CIs provide access to speech information, albeit in a highly degraded form. This degradation can frequently make individual words unclear. While predictive sentence contexts can often be used to resolve individual unclear words, there are many factors that either enhance or diminish the benefit of sentence contexts. This dissertation presents three complementary studies designed to address some of these factors, specifically: (1) the location of the unclear word in the context sentence, (2) how much background noise is present, and (3) individual factors such as age and hearing loss. The first study assessed the effect of context for adult listeners with acoustic hearing when a target word is presented in different levels of background noise at the beginning or end of sentences that vary in predictive context. Both context sentences and target words were spectrally degraded as a simulation of sound processed by a CI. The second study evaluated how listeners with CIs use context under the same conditions of background noise, sentence position, and predictive contexts as the group with acoustic hearing. The third study used eye-tracking methodology to infer information about the real-time processing of degraded speech across ages in a group of people who had acoustic hearing and a group of people who used CIs. Results from these studies indicate that target words at the beginning of the context sentence are more likely to be interpreted to be consistent with the following context sentence than target words at the end of the context sentences. In addition, the age of the listener interacted with some of the other experimental variables to predict phoneme categorization performance and response times in both listener groups. In the study of real-time language processing, there were no significant differences in the gaze trajectories between listeners with CIs and listeners with acoustic hearing. Together, these studies confirm that older listeners can use context in a manner similar to younger listeners, although at a slower speed. These studies expand the field’s knowledge of the importance of an unclear word’s location within a sentence and draw attention to the strategies employed by individual listeners to use context. The results of these experiments provide vital data needed to assess the current usage of context in the aging population with CIs and to develop age-specific auditory rehabilitation efforts for improved communication.Item Fish Bioacoustics: From Basic Science to Policy(2024) Colbert, Benjamin; Bailey, Helen R; Popper, Arthur N; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sound is critically important to fishes. Sound is used to communicate with conspecifics, to detect predators and prey, or to otherwise understand the world around them. Within this dissertation, I used a variety of methods to investigate multiple aspects of fish bioacoustics, including hearing, hearing in noise, the effects of anthropogenic sound, and the morphology of peripheral auditory structures.In Chapter 2, I reviewed international policy on the regulation of underwater sound and the effects of underwater sound on marine and aquatic habitats. I found that while there are increasing efforts to regulate underwater noise, the policy efforts are hampered by a lack of quantifiable metrics associated with impacts of anthropogenic sound in aquatic habitats and species. In Chapter 3, I measured auditory sensitivity of cyprinids using physiological methods. Auditory evoked potentials, a physiological measure of auditory sensitivity, have been used in previous studies to measure hearing sensitivity. However, while physiological methods have their place, they are measuring the sensitivity of the ear rather than the entirety of the auditory pathway. Therefore, I further measured hearing sensitivity of goldfish using behavioral methods that encompass the full auditory pathway. I found that physiological methods tend to underestimate actual hearing sensitivity at frequencies less than 1000 Hz. In Chapter 4, I investigated cyprinid hearing in noise, using both physiological and behavioral measures. Critical ratios were measured for four species of carp and goldfish using auditory evoked potentials. Behavioral methods were also used to measure critical ratios for goldfish. These data represent the first measurements of critical ratios for carp and the first comparative analysis between critical ratios measured using both physiology and behavior. I found that critical ratios for carp increase by as much as 25 dB between 300 Hz and 1500 Hz. I also found that physiological methods likely overestimate actual critical ratios for fish. In Chapter 5, I used micro-computed tomography (micro-CT) and three dimensional geometric morphometrics to compare the peripheral auditory structures of three species of carp. Three dimensional models of the tripus ossicle, the posterior most Weberian ossicle, and the sagitta otolith were created and the shape of these structures for silver carp (Hypophthalmichthys molitrix), bighead carp (H. noblis), and grass carp (Ctenopharyngodon idella) quantified and contrasted. I found that the shape of the tripus differed between the Hypophthalmichthys genus (i.e., silver and bighead carp) and Ctenopharyngodon (grass carp), demonstrating a possible phylogenetic signal in the shape of the Weberian ossicles. In Chapter 6, I studied the response of wild oyster toadfish (Opsanus tau) to underwater radiated noise from boats. I used passive acoustic monitoring to record toadfish vocalizations and vessel passages in the Chesapeake Bay, U.S.A. The effect of acute vessel passage was determined by comparing the number of calls after a vessel had passed to a control period. The effect of both aggregate vessel passage over an hour and environmental variables were investigated using generalized additive mixed models. I found that there was no significant effect on toadfish call rates from acute vessel passage but when vessel generated sound was higher over an hour long period (i.e., aggregate effect), call rate declined.Item The Nanoarchitecture of the Outer Hair Cell Lateral Wall: Structural Correlates of Electromotility(2021) Sun, Willy Weiyih; Carr, Catherine; Kachar, Bechara; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Proper mammalian hearing depends on an outer hair cell-based mechanism that amplifies the sound-induced travelling waves in the cochlea. Outer hair cells (OHCs) contribute to this cochlear amplification through their electromotile property—voltage-dependent somatic length changes that can operate at acoustic frequencies. This unique form of motility is driven by prestin, a member of the solute carrier 26 family of anion transporters that is highly expressed along the OHC lateral plasma membrane. The lateral plasma membrane is supported by a cortical actin-spectrin lattice and a smooth ER system known as lateral cisternae to form a regular layered structure along the entire OHC lateral wall. The detailed structural organization of each layer and how they interact to transduce prestin conformational changes into whole-cell motility are not well understood. In this dissertation, I combine cryogenic sample preparation methods and electron tomography to elucidate the functional architecture of the OHC lateral wall complex. In chapter 1, I review the biology of the mammalian auditory system. In chapter 2, I detail how the combined methodological approach used can preserve and reveal the three-dimensional nano-architectures in cells at near-native state. In chapter 3, I describe the successful use of this methodology to elucidate the structure-function relationships in a comparable model structure, the glycocalyx on the surface of enterocytes. In Chapter 4, I provide the details on the organization of each layer of the OHC lateral wall complex and how they are structurally integrated. I show that the lateral plasma membrane contains closely tiled microdomains of orthogonally packed putative prestin protein complexes. The cortical lattice connects the plasma membrane to the adjacent lateral cisternae through two independent cross-bridging components. The lateral cisternae are in turn integrated through inter and intra-cisternal cross-bridging systems. Finally, mitochondria are attached to the lateral cisternae through another set of linker elements. By quantifying the dimensions of each of these components and mapping their distribution I provide a detailed blueprint of the nano-architecture of the OHC electromotile apparatus and discuss how its cohesive structure allows effective transmission of forces generated by prestin to the rest of the cell to drive cochlear amplification.