Browsing by Author "Cox, Steven J"

Now showing 1 - 4 of 4
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    Dynamics of brain networks during reading
    (2015-10-05) Whaley, Meagan; Cox, Steven J; Dabaghian, Yuri; Kemere, Caleb; Tandon, Nitin
    We recorded electrocorticographic (ECoG) data from 15 patients with intractable epilepsy during a word completion task to precisely describe the spatiotemporal brain dynamics underlying word reading. Using a novel technique of analyzing grouped ECoG, cortical regions distributed throughout the left hemisphere were identified as significantly active versus baseline during our word stem completion task. Regions of activity spread from fusiform to frontal regions, including pars opercularis, pars triangularis, and pre, post, and subcentral gyri during the time period approaching articulation onset. The ECoG data recorded from electrodes within these regions were fit into linear multivariate autoregressive models, which precisely reveal the time, frequency, and magnitude of information flow between localized brain regions. Grouped network dynamics were quantified with two metrics of evaluating statistical significance of post-stimulus interactions compared to baseline. Results from both methods reveal bidirectional exchanges between frontal regions with fusiform, supporting theories which incorporate top-down and bottom-up processing during single word reading.
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    Sound-to-Touch Sensory Substitution and Beyond
    (2015-06-29) Novich, Scott David; Eagleman, David M; Baraniuk, Richard G; Burrus, Charles S; Cox, Steven J; O'Malley, Marcia K
    Deafness affects an estimated 2 million people in the United States and 53 million worldwide. Cochlear implants are an effective therapeutic solution but suffer from a number of drawbacks: they are expensive, require an invasive surgery, have low efficacy in early-onset deaf adults, and not everyone who needs them may qualify for them. This creates a large unmet need for a solution that is affordable, non-surgical, and works in adults. "Sensory substitution"--the concept that information can be effectively mapped from one sense to another--has the potential to overcome all of these issues: it is non-invasive (and therefore inexpensive and less regulated) and leverages a developed sensory modality. This is realized by the understanding that (1) the nervous system ultimately encodes information as electrical signals and (2) the brain has the remarkable capability of cortical reorganization. Sensory substitution has previously been successfully applied as a solution for blindess via vision-to-touch substitutions. To this end, a sound-to-touch sensory substitution device, The Versatile Extra-Sensory Transducer (VEST), has been developed for this thesis-work as a means for overcoming deafness. The device consists of a smartphone that takes sound from the environment and converts this information to patterns of vibration on the torso. This occurs via an array of vibratory motors embedded on a vest that is worn under the user's clothing. It is capable of giving congenitally deaf individuals the ability to intuit speech. The development of this device serves as a motivating example for a more general guiding framework that applies to sensory substitution and augmentation devices.
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    Spectral Analysis of One-Dimensional Operators
    (2015-02-25) Fillman, Jacob D; Damanik, David T; Hardt, Robert M; Cox, Steven J
    We study the spectral analysis of one-dimensional operators, motivated by a desire to understand three phenomena: dynamical characteristics of quantum walks, the interplay between inverse and direct spectral problems for limit-periodic operators, and the fractal structure of the spectrum of the Thue-Morse Hamiltonian. Our first group of results comprises several general lower bounds on the spreading rates of wave packets defined by the iteration of a unitary operator on a separable Hilbert space. By using tools within the class of CMV matrices, we apply these general lower bounds to deduce quantitative lower bounds for the spreading of the time-homogeneous Fibonacci quantum walk. Second, we construct several classes of limit-periodic operators with homogeneous Cantor spectrum, which connects problems from inverse and direct spectral analysis for such operators. Lastly, we precisely characterize the gap structure of the canonical periodic approximants to the Thue-Morse Hamiltonian, which constitutes a first step towards understanding the fractal structure of its spectrum. This thesis contains joint work with David Damanik, Milivoje Lukic, Paul Munger, and Robert Vance.
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    The large scale geometry of strongly aperiodic subshifts of finite type
    (2015-04-22) Cohen, David Bruce; Putman, Thomas Andrew; Cox, Steven J; Veech, William A
    A subshift on a group G is a closed, G-invariant subset of A to the G, for some finite set A. It is said to be of finite type if it is defined by a finite collection of “forbidden patterns” and to be strongly aperiodic if it has no points fixed by a nontrivial element of the group. We show that if G has at least two ends, then there are no strongly aperiodic subshifts of finite type on G (as was previously known for free groups). Additionally, we show that among torsion free, finitely presented groups, the property of having a strongly aperiodic subshift of finite type is invariant under quasi isometry.