UMD Theses and Dissertations
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Item SENSORY AND HORMONAL MECHANISMS OF EARLY LIFE BEHAVIOR IN A SOCIAL CICHLID FISH(2024) Westbrook, Molly; Juntti, Scott; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Studying the ontogeny of animal behavior is fundamental to ethology and allows understanding how behaviors in early life may affect later life success. The social cichlid Astatotilapia burtoni is an excellent model for examining the mechanisms of early life aggression due to the robust social hierarchy enforced by stereotyped, measurable social behaviors. We examine how hormonal signaling affects early life aggression through pharmacology and CRISPR-Cas9 mutants. We test which sensory pathways convey aggression-eliciting stimuli through sensory deprivation experiments. And we identify kinematic features that predict aggression through machine-learning video tracking algorithms. We observe that aggressive behaviors emerge around 17 days post fertilization (dpf), correlating with when the animals transition to free swimming away from the mother. We find that sex steroids subtly organize behavioral circuits for aggression and suggest that unknown additional mechanisms play a leading role. We show that thyroid hormone is not necessary or sufficient for the transition to aggressive behavior. We show that visual signals are necessary for the full expression of aggression, but in the absence of visual signal, low levels of aggression remain. We show that ciliated olfactory receptor signaling maintains low levels of aggression, as mutant animals display higher levels of aggressive behavior between 17 and 24 dpf. Finally, we demonstrate that swimming velocity has potential to predict aggressive instances of behavior. Together, we find multiple levels of control for early life aggressive bouts from sensory input to hormonal organization of brain circuits.Item Machine Learning with Differentiable Physics Priors(2024) Qiao, Yiling; Lin, Ming ML; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Differentiable physics priors enable gradient-based learning systems to adhere to physical dynamics. By making physics simulations differentiable, we can backpropagate through the physical consequences of actions. This pipeline allows agents to quickly learn to achieve desired effects in the physical world and is an effective technique for solving inverse problems in physical or dynamical systems. This new programming paradigm bridges model-based and data-driven methods, mitigating data scarcity and model bias simultaneously. My research focuses on developing scalable, powerful, and efficient differentiable physics simulators. We have created state-of-the-art differentiable physics for rigid bodies, cloth, fluids, articulated bodies, and deformable solids, achieving performance orders of magnitude better than existing alternatives. These differentiable simulators are applied to solve inverse problems, train control policies, and enhance reinforcement learning algorithms.Item EXPLORING NEURAL REPRESENTATIONS IN MACAQUE PRIMARY VISUAL CORTEX THROUGH DATA-DRIVEN MODELS(2024) Bartsch, Felix; Butts, Daniel A; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The study of the primary visual cortex (V1) holds profound significance for our understanding of the neural underpinnings of visual perception. Computational models have emerged as invaluable tools to decode the intricate computations occurring within V1 neurons. This dissertation embarks on a comprehensive exploration of V1 by fitting statistical models to electrophysiological data and scrutinizing model properties. My approach not only provides direct insights into how V1 neurons represent information but also furnishes mathematical descriptions of V1 computations, thereby contributing to the construction of a unified model of V1 function.I begin in Chapter 2 by employing state-of-the-art statistical and machine learning techniques to unravel the high-resolution components of V1 receptive fields as they respond to random bar stimuli. I demonstrate how these models not only replicate classical findings but also offer superior explanations of the computations V1 undertakes. These results highlight how the simultaneous processing of multiple overlapping inputs enables cells to represent high-resolution information while also responding to full-field inputs, an intricate organization unattainable using conventional stimuli. In chapter 3, I expand this modeling approach by adding mechanisms for binocular integration and apply them to data obtained from random bar stimuli that also vary in binocular disparity. This approach reveals that V1 disparity selectivity is enhanced and well characterized using spatial convolutions. Finally, I further modify the approach in chapter 4 to map spatiotemporal receptive fields in luminance and color using data recorded from the fovea and present the first spatiochromatic measurements illustrating the scale of V1 processing at the fovea. I find that color signals operate at lower spatial scales compared to luminance signals, and that receptive field substructure can allow even cells with large receptive fields to represent fine-scale information throughout the fovea.Item EARLY CHRONIC MONOCULAR VISUAL DEPRIVATION COMPROMISES THE RETINAL FUNCTION OF THE DEPRIVED EYE(2020) Ara, Jawshan; Quinlan, Elizabeth M.; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Amblyopia is caused by abnormal visual experience during early childhood such as unilateral cataract, strabismus, and anisometropia. The misalignment of the images in the case of strabismus or blurriness/haziness of the image quality originating from the defective eye results in reduced visual acuity and contrast sensitivity in the deprived eye (Volkers et al., 1987) in comparison to the non-deprived eye and limits stereopsis in humans (Husk et al., 2012). Most clinical treatments for amblyopia penalize the fellow eye to bias the visual system towards the input from the amblyopic eye. Unfortunately, current clinical treatments for amblyopia are most effective in children younger than 7 years old (Cotter et al., 2012). Works in animal models of amblyopia are beginning to identify ways to improve vision in adult amblyopes. They have focused almost exclusively on deficits in the functions of the visual cortex. However, dark rearing can reduce the amplitude of the photopic Electroretinogram indicating reduced functions of cone-mediated retinal functions and alter the mGluR6 distribution and intensity in the first synapses between cone photoreceptors and ON bipolar cells (Dunn et al., 2013). It is predicted but not yet tested, that monocular deprivation will have a similar impact on retinal functions. Here we characterize various aspects of the effect of chronic monocular deprivation (cMD) on retinal functions in adult mice. We observed that chronic monocular deprivation significantly reduced electroretinogram (ERG) response originating from the inner retinal plexiform layer of the deprived eye retina in comparison to the non-deprived eye retina. Our observation suggests that early chronic visual deprivation compromises the retinal function of the deprived eye of the adult mice.Item PARENT PERSPECTIVES ON DIAGNOSIS OF AND SERVICES FOR CHILDREN WITH CORTICAL VISUAL IMPAIRMENT(2019) Kempler, Sara Kathleen; Beckman, Paula J; Special Education; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Medical advances in recent years have increased survival rates of infants born prematurely and/or infants and children that present with life-threatening conditions (Good et al., 1994; Khetpal & Donahue, 2007; Murphy & Carbone, 2011). These increased survival rates are associated with an increase in the number of children who have severe and/or multiple disabilities, including those conditions that are associated with cortical visual impairment. Children with typical or nearly typical eye exams, but having observable visual impairment are those generally diagnosed with cortical visual impairment, or CVI (Jan, Groenveld, Sykanda, & Hoyt, 1987). Delayed or lack of diagnosis of CVI can lead to missed opportunities for learning, and especially missed sensitive periods during which recovery can occur faster (Hubel & Wiesel, 1970; Roman-Lantzy, 2018). Without diagnosis, children may not be eligible for funding assistance for educational materials (American Printing House for the Blind, n.d.b). The purpose of this study was to explore parents’ experiences in getting a diagnosis of CVI for their children. For example, whether there were lapses in time between suspected vision difficulties and diagnosis, and what information was provided when diagnosis was obtained. The research questions guiding this investigation included: What are parents’ experiences in seeking a diagnosis for their child’s suspected vision challenges? What needs do parents recall related to information and supports while seeking a diagnosis for their child’s suspected vision challenges? What kind of information is offered or readily available to parents upon diagnosis of CVI? The primary data source for this study was interviews with parents of children having diagnosed CVI. Secondary data sources included interviews with ophthalmologists, teachers of the visually impaired, and records review.Item CHARACTERIZATION OF CHRONIC MONOCULAR DEPRIVATION AND ESTROGEN ADMINISTRATION IN ADULT RODENTS(2018) Sengupta, Deepali Clare; Quinlan, Elizabeth M; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Reduced synaptic plasticity and excitatory synapse density contribute to age-related cognitive decline, and constrain recovery of function from injury in adults. A parallel reduction in circulating sex hormones in both sexes, particularly estrogens, exacerbates this decline in synaptic plasticity. Conversely, estrogen therapy in aged members of many species restores synapse density, promotes synaptic plasticity, and improves learning/memory. Importantly, acute estrogen administration can promote rapid synaptogenesis, and these new synapses can be stabilized by activity. Here I ask if estrogen treatment can promote synaptic plasticity in the primary visual cortex (V1) of aged rats. I demonstrate robust expression of estrogen receptors (ERs) in V1 of adult male and female rats, suggesting an opportunity to enhance plasticity with estrogens. I test this hypothesis following the induction of amblyopia by chronic monocular deprivation (cMD). I show that cMD reduces thalamic innervation from the deprived eye, and increases molecular markers which constrain plasticity, consistent with observations that the deficits induced by cMD are highly resistant to reversal. Surprisingly, cMD did not change markers for excitatory synapses, suggesting a homeostatic increase in synapses serving the non-deprived eye (NDE) to maintain synaptic density within an optimal range. Importantly, visually-evoked potentials (VEPs) induced by repetitive visual stimulation to the deprived eye depress more rapidly than those of the NDE, consistent with cMD inducing an increase in the probability of neurotransmitter release (Pr) at synapses in the cMD pathway. In contrast, treatment of cMD adults with a single dose of 17α estradiol significantly increased markers for excitatory synapses, and estradiol treatment followed by visual stimulation also increased markers for excitatory synapse activity. Repetitive estradiol treatments increased excitatory synapse markers, but not synaptic activity markers. Furthermore, one dose of estradiol enhanced VEP amplitude following repetitive visual stimulation, however this was observed only in response to stimulation of the NDE. As presynaptic ERs are known to increase Pr at glutamatergic synapses, this suggests that the effects of estradiol are specific to spared synapses where Pr has not been up-regulated by deprivation. Exploiting this selectivity may allow for receptive field remapping of spared inputs around a scotoma or cortical infarctItem Architecture Without Vision(2015) Nolen, Elizabeth; Simon, Madlen; Architecture; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)What is architecture if you cannot see? How might we perceive if we ignore our dominant visual sense to focus on inputs from the senses that we rarely engage as we move through the built environment? How might architects design buildings to fully engage our senses? This thesis began to address that question through research including a literature search, analysis of examples of architecture for visually impaired users, and interviews with blind individuals and people who work with visually impaired people. This research informed the development of a set of principles for the design of built environments that enrich the ability to people along the spectrum from sighted to blind to navigate the spaces of their lives through multi-sensory perception. These principles are tested by application to the design of a building, a Creative Co-Lab, in which blind and sighted users come together on the Baltimore waterfront to learn collaboratively about the multi-sensory ways to perceive and create space, place, and objects without vision.Item HIERARCHICAL NEURAL COMPUTATION IN THE MAMMALIAN VISUAL SYSTEM(2015) Cui, Yuwei; Butts, Daniel A; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Our visual system can efficiently extract behaviorally relevant information from ambiguous and noisy luminance patterns. Although we know much about the anatomy and physiology of the visual system, it remains obscure how the computation performed by individual visual neurons is constructed from the neural circuits. In this thesis, I designed novel statistical modeling approaches to study hierarchical neural computation, using electrophysiological recordings from several stages of the mammalian visual system. In Chapter 2, I describe a two-stage nonlinear model that characterized both synaptic current and spike response of retinal ganglion cells with unprecedented accuracy. I found that excitatory synaptic currents to ganglion cells are well described by excitatory inputs multiplied by divisive suppression, and that spike responses can be explained with the addition of a second stage of spiking nonlinearity and refractoriness. The structure of the model was inspired by known elements of the retinal circuit, and implies that presynaptic inhibition from amacrine cells is an important mechanism underlying ganglion cell computation. In Chapter 3, I describe a hierarchical stimulus-processing model of MT neurons in the context of a naturalistic optic flow stimulus. The model incorporates relevant nonlinear properties of upstream V1 processing and explained MT neuron responses to complex motion stimuli. MT neuron responses are shown to be best predicted from distinct excitatory and suppressive components. The direction-selective suppression can impart selectivity of MT neurons to complex velocity fields, and contribute to improved estimation of the three-dimensional velocity of moving objects. In Chapter 4, I present an extended model of MT neurons that includes both the stimulus-processing component and network activity reflected in local field potentials (LFPs). A significant fraction of the trial-to-trial variability of MT neuron responses is predictable from the LFPs in both passive fixation and a motion discrimination task. Moreover, the choice-related variability of MT neuron responses can be explained by their phase preferences in low-frequency band LFPs. These results suggest an important role of network activity in cortical function. Together, these results demonstrated that it is possible to infer the nature of neural computation from physiological recordings using statistical modeling approaches.Item Evolution and Significance of Sexual Display in Ptilonorhynchidae(2012) Coyle, Brian James; Borgia, Gerald; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There is spectacular diversity of sexual displays among taxa. Charles Darwin was first to suggest that these traits have arisen through sexual selection (Darwin 1871). The theory of sexual selection addresses competition for mates that occurs within and between sexes (i.e. mate choice) and leads to variation in individual reproductive success. Darwin's insights into display evolution and mate choice were largely rejected by Alfred Russell Wallace (1878), who independently conceived of Natural Selection, and were controversial for decades but are now a cornerstone of evolutionary theory. The important role of sexual displays in mate choice has been demonstrated by extensive research in many species (e.g. Andersson 1994). Although the importance of sexual displays is well established, display evolution remains a controversial topic and active area of research. Multiple hypotheses have been offered to explain the evolution of sexual displays. The "good genes" hypothesis suggests displays communicate reliable information about male quality that allows females to make informed comparisons between potential mates and choose the best one (e.g. Fisher, 1915; Hamilton and Zuk,1982; Maynard Smith, 1976). These indicators of male quality may become costly to produce and maintain and expose the bearer to increased risk. The "handicap" hypothesis predicts that the inherent cost of certain displays and the variation among males in their ability to bear those costs ensure that the traits are honest indicators of relative male quality (Zahavi 1975, 1977). "Runaway selection" is a competing hypothesis that suggests displays evolve through a non-adaptive process that, in most models, is sustained by genetic correlation between display and preference (Fisher, 1930; Lande, 1981, 1987). Display elaboration via run-away is driven by open-ended preference and limited by natural selection. Sensory drive is a theory of signal evolution that addresses display design or form, including characteristics such as color, pattern, and frequency (e.g. Lythgoe, 1979; Endler, 1992a,b; Endler and Basolo, 1998). Sensory drive shapes displays to maximize communication efficiency within the particular constraints of local habitat parameters and sensitivities of the sensory system that receive the display. Thus, differences in display design are largely attributed to variation in habitats and sensory abilities among taxa. For example, display color differences among bird species may be due to the variation in habitat light spectral composition and differences in their visual spectral sensitivity (see Hill and McGraw, 2006). A variation of sensory drive called sensory exploitation suggests that males may evolve displays that take advantage of sensory biases which have evolved in other behavioral contexts, such as foraging, to manipulate females into mating (Ryan and Rand, 1990; Kirkpatrick and Ryan, 1991; Endler and Basolo, 1995). Sensory exploitation may be mal-adaptive for females if the display is not somehow correlated with male quality and may therefore lead to selection on females to eliminate or avoid susceptibility to the display. In this dissertation, I explore the evolution and development of sexual displays in species of bowerbirds, family Ptilonorhynchidae. Most bowerbirds are polygynous species with lek-like mating systems. They have long been an important model for studying sexual selection (e.g. Darwin, 1971; Marshall, 1954; Gilliard, 1969; Borgia, 1985; Frith et al, 2004). Females are highly selective in choosing mates and mating success is strongly skewed among males (e.g. Borgia, 1985; Borgia 1992). Males display in various modalities and express morphological, behavioral and off-body elements. They build a courtship structure called a bower that provides protection to females from forced copulation as they attend to behavioral display. Males decorate their bower and the surrounding display court with objects of various type and color that they collect from their environment and arrange in specific patterns (e.g. Borgia, 1985; Diamond, 1987; Lenz, 1994; Madden et al. 2004; Endler et al., 2005; Endler and Day, 2006; Borgia, 2008). They also destroy bowers of other males and plunder decorations (e.g. Borgia, 1985b; Borgia and Mueller, 1992). Courtship consists of vocalizations, behavioral elements and displays of their colorful plumage. All display types are highly differentiated throughout the bowerbird family and studies in multiple species reveal a strong correlation between mating success and many display elements (e.g. Borgia, 1985; Borgia, 1992; Madden, 2003; Frith et al. 2004). Display development in bowerbirds is complex and is thought to involve an extensive learning component (e.g. Marshall, 1954; Borgia, 1986; Loffredo and Borgia, 1986; Diamond, 1988; Frith et al., 2004; Madden, 2008; Endler et al., 2010). Bowerbirds are long lived species and males are not fully mature until more than five years old. During their juvenile period they observe the displays of adult males and practice display with other juveniles. Many species are also excellent vocal mimics demonstrating that learning is involved at least in vocal display acquisition (e.g. Loffredo and Borgia, 1986; Coleman et al., 2007; Kelly and Healy, 2010). In chapter one, I test the sensory drive hypothesis in bowerbirds by investigating the relationship between visual spectral sensitivity and the color of plumage and decoration displays. Bowerbirds have strong and specific color preferences and dislikes that differ between species. Sensory drive suggests that these differences may be driven by variation in spectral sensitivity that has arisen as a result of local adaptation to habitat (Endler 1992b). Spectrophotometry and microspectrophotometry were used to measure spectral transmission through ocular media (lens, cornea, and aqueous humor) and measure sensitivity of retinal photoreceptors that include four spectrally distinct cone receptors involved in color vision. I also used fluorescent microscopy to quantify the relative number of cone types from mounted retinal tissue. Furthermore, I sequenced the genes that code for opsin pigments to estimate photoreceptor spectral sensitivity. I found no differences in spectral sensitivity among 13 species that would explain the large interspecific variation in display coloration. However, I did find that bowerbird's lenses are relatively transparent to ultraviolet (UV) wavelengths which could influence the evolution of UV reflective displays. In chapter two, I investigated the occurrence of natural hybridization between two bowerbird species, Chlamydera nuchalis and C. maculata. In other sympatric species of bowerbirds hybridization is rare or absent which may be attributable to prezygotic reproductive isolation that is due to large differences in appearance and display (see Coyne and Orr, 2004). In this study I detected over 20% hybrid individuals based on phenotype analysis. I also provide evidence of mitochondrial introgression and show that females of both species hybridize. Given that females show a high degree of effort in intraspecific mate choice (Borgia, 1995a; Madden, 2003) it is not clear why they would mate with males of another species. Based on the distribution of bowers throughout the contact zone, it does not appear that females lack access to males of their own species, which is one of the more common reasons that bird species hybridize. Studies of other avian hybrid systems show that display learning between species drives hybridization. I provide behavioral evidence that male bowerbirds in this contact zone may learn displays from the other species. In chapter three I investigate hypotheses about the design of decoration displays. Recent work suggests that great bowerbirds, Chlamydera nuchalis, arrange objects to create a visual illusion called Forced Perspective that attracts females and increases male mating success (Endler et al. 2010; Kelly and Endler, 2012a,b). According to this hypothesis males arrange objects from small to large with distance from the bower to create an even size gradient such that all objects subtend the same visual angle to the female eye. The supposed effect is to make all objects appear the same size and make displays in the foreground appear closer. However, the data from these studies does not support the claim that males do create even size gradients nor does it show a link between the supposed illusion and mating success (Anderson, 2012; Borgia et al., 2012). I hypothesize that males are simply placing smaller objects closer to the bower for the practical purpose of avoiding interference from obstacles during courtship display. I conducted a survey of human subjects who assessed patterns of size-related bower decoration design. Survey participants were instructed to evaluate the size related pattern of object distribution in decoration displays based on visual examination of digital images. I included 40 bowers from great (C. nuchalis) spotted (C. maculata) and western (C. gutatta) bowerbirds, which share similar decoration schemes. Results of this study do not support either hypothesis, however I suggest that the obstacle avoidance hypothesis may be challenging for naive observers to detect.Item Theory, Design, and Implementation of Landmark Promotion Cooperative Simultaneous Localization and Mapping(2011) Karvounis, John George; Blankenship, Gilmer; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Simultaneous Localization and Mapping (SLAM) is a challenging problem in practice, the use of multiple robots and inexpensive sensors poses even more demands on the designer. Cooperative SLAM poses specific challenges in the areas of computational efficiency, software/network performance, and robustness to errors. New methods in image processing, recursive filtering, and SLAM have been developed to implement practical algorithms for cooperative SLAM on a set of inexpensive robots. The Consolidated Unscented Mixed Recursive Filter (CUMRF) is designed to handle non-linear systems with non-Gaussian noise. This is accomplished using the Unscented Transform combined with Gaussian Mixture Models. The Robust Kalman Filter is an extension of the Kalman Filter algorithm that improves the ability to remove erroneous observations using Principal Component Analysis (PCA) and the X84 outlier rejection rule. Forgetful SLAM is a local SLAM technique that runs in nearly constant time relative to the number of visible landmarks and improves poor performing sensors through sensor fusion and outlier rejection. Forgetful SLAM correlates all measured observations, but stops the state from growing over time. Hierarchical Active Ripple SLAM (HAR-SLAM) is a new SLAM architecture that breaks the traditional state space of SLAM into a chain of smaller state spaces, allowing multiple robots, multiple sensors, and multiple updates to occur in linear time with linear storage with respect to the number of robots, landmarks, and robots poses. This dissertation presents explicit methods for closing-the-loop, joining multiple robots, and active updates. Landmark Promotion SLAM is a hierarchy of new SLAM methods, using the Robust Kalman Filter, Forgetful SLAM, and HAR-SLAM. Practical aspects of SLAM are a focus of this dissertation. LK-SURF is a new image processing technique that combines Lucas-Kanade feature tracking with Speeded-Up Robust Features to perform spatial and temporal tracking. Typical stereo correspondence techniques fail at providing descriptors for features, or fail at temporal tracking. Several calibration and modeling techniques are also covered, including calibrating stereo cameras, aligning stereo cameras to an inertial system, and making neural net system models. These methods are important to improve the quality of the data and images acquired for the SLAM process.