Theses and Dissertations from UMD
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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.Item Age Effects on Perceptual Organization of Speech in Realistic Environments(2017) Bologna, William Joseph; Dubno, Judy R; Gordon-Salant, Sandra; Hearing and Speech Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Communication often occurs in environments where background sounds fluctuate and mask portions of the intended message. Listeners use envelope and periodicity cues to group together audible glimpses of speech and fill in missing information. When the background contains other talkers, listeners also use focused attention to select the appropriate target talker and ignore competing talkers. Whereas older adults are known to experience significantly more difficulty with these challenging tasks than younger adults, the sources of these difficulties remain unclear. In this project, three related experiments explored the effects of aging on several aspects of speech understanding in realistic listening environments. Experiments 1 and 2 determined the extent to which aging affects the benefit of envelope and periodicity cues for recognition of short glimpses of speech, phonemic restoration of missing speech segments, and/or segregation of glimpses with a competing talker. Experiment 3 investigated effects of age on the ability to focus attention on an expected voice in a two-talker environment. Twenty younger adults and 20 older adults with normal hearing participated in all three experiments and also completed a battery of cognitive measures to examine contributions from specific cognitive abilities to speech recognition. Keyword recognition and cognitive data were analyzed with an item-level logistic regression based on a generalized linear mixed model. Results indicated that older adults were poorer than younger adults at glimpsing short segments of speech but were able use envelope and periodicity cues to facilitate phonemic restoration and speech segregation. Whereas older adults performed poorer than younger adults overall, these groups did not differ in their ability to focus attention on an expected voice. Across all three experiments, older adults were poorer than younger adults at recognizing speech from a female talker both in quiet and with a competing talker. Results of cognitive tasks indicated that faster processing speed and better visual-linguistic closure were predictive of better speech understanding. Taken together these results suggest that age-related declines in speech recognition may be partially explained by difficulty grouping short glimpses of speech into a coherent message, which may be particularly difficult for older adults when the talker is female.Item The Cellular Basis for Hearing(2010) Sul, Bora; Roy, Rajarshi; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hair cells constitute the cellular basis for hearing. Their primary role is to convert mechanical signal into electrical signal through the ion channels, called ``mechano-electrical transducer (MET) channels'', in the hair bundles of hair cells. Another important function of hair cells is to reciprocally amplify the mechanical input signal by working against damping due to viscous fluids in the organ. This thesis consists of theoretical investigations on hair cell function as the mechano-electrical transducer and as the cochlear amplifier. First, we examine gating of two MET channels that are coupled to each other. While gating of MET channels has been successfully described by assuming that in a hair bundle, one MET channel is associated with one tip link, recent reports indicate that a single tip link is associated with more than one channel cite{Beurg2006,Beurg2009}. To address the discrepancy between the earlier models with the recent experimental observations, we describe gating of MET channels by assuming that each tip link is associated with two identical MET channels, which are connected either in series or in parallel. We found that series connection model predicts double minima of the hair bundle stiffness with respect to the hair bundle displacement if the minimum is below a certain positive value. In contrast, the parallel connection model makes predictions similar to the previous model that assumes a single channel for each tip link, within the physiological range of parameters. This explains how the earlier models assuming a single channel for each tip link has been successful in describing gating of MET channels. The parallel connection model of MET channels is, therefore, a reasonable assumption to explain most experimental observations. However, we show that turtle hair cell data may be compatible with the series connection model. Second, we examine roles of hair cells as an amplifier in the cochlea. Hair cells are responsible for high sensitivity and frequency selectivity of hearing. This is attributed to motile mechanisms in hair cells, ``electromotility'' which indicates length change of outer hair cell driven by AC electrical potential across the membrane, and ``hair bundle motility'' which is an active movement of the hair bundle of hair cells. We first investigated the amplifying role of hair cells in the mammalian ear, including studies of both electromotility and hair bundle motility. Electromotility is driven by the receptor potential, which is an AC electrical potential generated by gating of MET channels. Thus, the frequency characteristics of electromotility are determined by a low-pass filter, represented by the product of membrane resistance R and capacitance C with frequency roll off at about 0.1 of the highest audible frequency. This filter significantly decreases the efficiency of electromotility as an amplifier. In the thesis, we examine a proposal that the cochlear microphonic, the voltage drop across the extracellular medium by the receptor current, contributes to overcome this problem. We found that this effect can improve the frequency response. However, this effect alone is too small to enhance the effectiveness of electromotility beyond 10 kHz in the mammalian ear. It has been experimentally found that the hair bundle motility in the mammalian ear is based on a ``release mechanism'', which is the fast component in the hair bundle's response to mechanical stimulation. In the release mechanism, the hair bundle responds in a way to reduce applied tension, similar to common mechanical relaxation with a damping. This observation is puzzling because hair bundle motility based on the release mechanism is expected to have an amplifying role. In the thesis we show that a release mechanism can indeed have a role in amplification if it takes place in a range where effective hair bundle stiffness has a negative value. Finally we expand scope of investigation to avian hair cells, which must rely on hair bundle motility for amplification due to lack of electromotility. Specifically we evaluate the effectiveness of hair bundle motility in mammalian and avian ears. If hair bundle motility works for amplification, energy generated by the hair bundle must be, at least, greater than energy lost due to damping in the viscous fluid of cochlea. We compare work done by the hair bundle motility with the energy loss due to shear in the sub-tectorial gap during one cycle of small sinusoidal hair bundle displacement. This condition gives a frequency limit where the hair bundle motility can work as an amplifier in the cochlea. We obtain frequency limits for two mechanisms for hair bundle motility; one is based on the interaction between calcium and the MET channel and the other is based on the interplay between gating of the channel and the myosin motor. We show that the frequency limit obtained for each of these models is an increasing function of a factor that is determined by the morphology of hair bundles and the cochlea. Primarily due to the higher density of hair cells in the avian inner ear, this factor is about 10-fold greater for the avian ear than the mammalian ear, which has much higher auditory frequency limit. This result is consistent with a much greater importance of hair bundle motility in the avian ear than that in the mammalian ear.