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On Kernel-base Multi-Task Learning
Title
On Kernel-base Multi-Task Learning.
Creator
Li, Cong, Georgiopoulos, Michael, Anagnostopoulos, Georgios, Tappen, Marshall, Hu, Haiyan, Ni, Liqiang, University of Central Florida
Abstract / Description
Multi-Task Learning (MTL) has been an active research area in machine learning for two decades. By training multiple relevant tasks simultaneously with information shared across tasks, it is possible to improve the generalization performance of each task, compared to training each individual task independently. During the past decade, most MTL research has been based on the Regularization-Loss framework due to its flexibility in specifying various types of information sharing strategies, the...
Show moreMulti-Task Learning (MTL) has been an active research area in machine learning for two decades. By training multiple relevant tasks simultaneously with information shared across tasks, it is possible to improve the generalization performance of each task, compared to training each individual task independently. During the past decade, most MTL research has been based on the Regularization-Loss framework due to its flexibility in specifying various types of information sharing strategies, the opportunity it offers to yield a kernel-based methods and its capability in promoting sparse feature representations.However, certain limitations exist in both theoretical and practical aspects of Regularization-Loss-based MTL. Theoretically, previous research on generalization bounds in connection to MTL Hypothesis Space (HS)s, where data of all tasks are pre-processed by a (partially) common operator, has been limited in two aspects: First, all previous works assumed linearity of the operator, therefore completely excluding kernel-based MTL HSs, for which the operator is potentially non-linear. Secondly, all previous works, rather unnecessarily, assumed that all the task weights to be constrained within norm-balls, whose radii are equal. The requirement of equal radii leads to significant inflexibility of the relevant HSs, which may cause the generalization performance of the corresponding MTL models to deteriorate. Practically, various algorithms have been developed for kernel-based MTL models, due to different characteristics of the formulations. Most of these algorithms are a burden to develop and end up being quite sophisticated, so that practitioners may face a hard task in interpreting and implementing them, especially when multiple models are involved. This is even more so, when Multi-Task Multiple Kernel Learning (MT-MKL) models are considered. This research largely resolves the above limitations. Theoretically, a pair of new kernel-based HSs are proposed: one for single-kernel MTL, and another one for MT-MKL. Unlike previous works, we allow each task weight to be constrained within a norm-ball, whose radius is learned during training. By deriving and analyzing the generalization bounds of these two HSs, we show that, indeed, such a flexibility leads to much tighter generalization bounds, which often results to significantly better generalization performance. Based on this observation, a pair of new models is developed, one for each case: single-kernel MTL, and another one for MT-MKL. From a practical perspective, we propose a general MT-MKL framework that covers most of the prominent MT-MKL approaches, including our new MT-MKL formulation. Then, a general purpose algorithm is developed to solve the framework, which can also be employed for training all other models subsumed by this framework. A series of experiments is conducted to assess the merits of the proposed mode when trained by the new algorithm. Certain properties of our HSs and formulations are demonstrated, and the advantage of our model in terms of classification accuracy is shown via these experiments.
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Date Issued
2014
Identifier
CFE0005517, ucf:50321
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005517
THE EFFECTS ON OPERATOR PERFORMANCE AND WORKLOAD WHEN GUNNERY AND ROBOTIC CONTROL TASKS ARE PERFORMED CONCURRENTLY
Title
THE EFFECTS ON OPERATOR PERFORMANCE AND WORKLOAD WHEN GUNNERY AND ROBOTIC CONTROL TASKS ARE PERFORMED CONCURRENTLY.
Creator
Joyner, Carla, McCauley-Bell, Pamela, University of Central Florida
Abstract / Description
The purpose of this research was to examine operator workload and performance in a high risk, multi-task environment. Specifically, the research examined if a gunner of a Future Combat System, such as a Mounted Combat System, could effectively detect targets in the immediate environment while concurrently operating robotic assets in a remote environment. It also analyzed possible effects of individual difference factors, such as spatial ability and attentional control, on operator performance...
Show moreThe purpose of this research was to examine operator workload and performance in a high risk, multi-task environment. Specifically, the research examined if a gunner of a Future Combat System, such as a Mounted Combat System, could effectively detect targets in the immediate environment while concurrently operating robotic assets in a remote environment. It also analyzed possible effects of individual difference factors, such as spatial ability and attentional control, on operator performance and workload. The experimental conditions included a gunner baseline and concurrent task conditions where participants simultaneously performed gunnery tasks and one of the following tasks: monitor an unmanned ground vehicle (UGV) via a video feed (Monitor), manage a semi-autonomous UGV, and teleoperate a UGV (Teleop). The analysis showed that the asset condition significantly impacted gunnery performance with the gunner baseline having the highest number of targets detected (M = 13.600 , SD = 2.353), and concurrent Teleop condition the lowest (M = 9.325 , SD = 2.424). The research also found that high spatial ability participants tended to detect more targets than low spatial ability participants. Robotic task performance was also affect by the asset condition. The results showed that the robotic target detection rate was lower for the concurrent task conditions. A significant difference was seen between the UGV-baseline (80.1%) when participants performed UGV tasks only and UGV-concurrent conditions (67.5%) when the participants performed UGV tasks concurrently with gunnery tasks. Overall, this study revealed that there were performance decrements for the gunnery tasks as well as the robotic tasks when the tasks were performed concurrently.
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Date Issued
2006
Identifier
CFE0000979, ucf:46704
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000979
Life Long Learning in Sparse Learning Environments
Title
Life Long Learning in Sparse Learning Environments.
Creator
Reeder, John, Georgiopoulos, Michael, Gonzalez, Avelino, Sukthankar, Gita, Anagnostopoulos, Georgios, University of Central Florida
Abstract / Description
Life long learning is a machine learning technique that deals with learning sequential tasks over time. It seeks to transfer knowledge from previous learning tasks to new learning tasks in order to increase generalization performance and learning speed. Real-time learning environments in which many agents are participating may provide learning opportunities but they are spread out in time and space outside of the geographical scope of a single learning agent. This research seeks to provide an...
Show moreLife long learning is a machine learning technique that deals with learning sequential tasks over time. It seeks to transfer knowledge from previous learning tasks to new learning tasks in order to increase generalization performance and learning speed. Real-time learning environments in which many agents are participating may provide learning opportunities but they are spread out in time and space outside of the geographical scope of a single learning agent. This research seeks to provide an algorithm and framework for life long learning among a network of agents in a sparse real-time learning environment. This work will utilize the robust knowledge representation of neural networks, and make use of both functional and representational knowledge transfer to accomplish this task. A new generative life long learning algorithm utilizing cascade correlation and reverberating pseudo-rehearsal and incorporating a method for merging divergent life long learning paths will be implemented.
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Date Issued
2013
Identifier
CFE0004917, ucf:49601
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004917
PLUNGERS AND PRODUCTIVITY: A STUDENT ARTIST'S SURVIVAL GUIDE TO MULTI-TASKING
Title
PLUNGERS AND PRODUCTIVITY: A STUDENT ARTIST'S SURVIVAL GUIDE TO MULTI-TASKING.
Creator
Wansa, Amanda, Chicurel, Steven, University of Central Florida
Abstract / Description
To be a fully functioning theatre practitioner, the developing student artist becomes equipped with a practical skill set that is ordinarily cultivated through formal training and study. Typically, organized study leads him/her to focus on a specific facet of the business: acting, directing, design, etc. However, students often develop a vast array of talents and skills within the profession and find themselves standing at a crossroads between what "kind" of artist to be; what singular aspect...
Show moreTo be a fully functioning theatre practitioner, the developing student artist becomes equipped with a practical skill set that is ordinarily cultivated through formal training and study. Typically, organized study leads him/her to focus on a specific facet of the business: acting, directing, design, etc. However, students often develop a vast array of talents and skills within the profession and find themselves standing at a crossroads between what "kind" of artist to be; what singular aspect of the arts on which to focus. Why not do it all? For those students who "do it all", there is an additional challenge: the artist who is a student immersed in daytime study and nighttime production obligations has to wear two caps. One is that of the learner and one is that of the employee, the producer, and perhaps even the teacher. When are these caps traded or are they both worn through all processes? This thesis will reveal my creative and practical processes from two productions at the University of Central Florida for which I played on- and offstage roles: I worked as a Sound Designer and featured actor in Sophie Treadwell's Machinal; I was the Vocal Director for Urinetown: The Musical, and also played Penelope Pennywise, a leading role. I will describe the challenges and successes of each project by examining the following evidence: my personal process with each piece, demonstrated through reflection and examples from the work; interviews with those involved in the productions as well as outside reviews and feedback; and research of each play. Research will include production history, intent of authors, and aspects that informed my work both onstage and off. Did multi-tasking sacrifice the quality of my work for any of my delegated tasks? Did I enjoy more success in my progress in time management, the ability to solve problems, and collaboration process with fellow artists, or in the actual on-stage products? What aspects of my training in my graduate program added to the quality of my work on these productions? Does being a multi-tasking artist help or hurt one's career in theatre?
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Date Issued
2009
Identifier
CFE0002579, ucf:48283
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002579
Improved Multi-Task Learning Based on Local Rademacher Analysis
Title
Improved Multi-Task Learning Based on Local Rademacher Analysis.
Creator
Yousefi, Niloofar, Mollaghasemi, Mansooreh, Rabelo, Luis, Zheng, Qipeng, Anagnostopoulos, Georgios, Xanthopoulos, Petros, Georgiopoulos, Michael, University of Central Florida
Abstract / Description
Considering a single prediction task at a time is the most commonly paradigm in machine learning practice. This methodology, however, ignores the potentially relevant information that might be available in other related tasks in the same domain. This becomes even more critical where facing the lack of a sufficient amount of data in a prediction task of an individual subject may lead to deteriorated generalization performance. In such cases, learning multiple related tasks together might offer...
Show moreConsidering a single prediction task at a time is the most commonly paradigm in machine learning practice. This methodology, however, ignores the potentially relevant information that might be available in other related tasks in the same domain. This becomes even more critical where facing the lack of a sufficient amount of data in a prediction task of an individual subject may lead to deteriorated generalization performance. In such cases, learning multiple related tasks together might offer a better performance by allowing tasks to leverage information from each other. Multi-Task Learning (MTL) is a machine learning framework, which learns multiple related tasks simultaneously to overcome data scarcity limitations of Single Task Learning (STL), and therefore, it results in an improved performance. Although MTL has been actively investigated by the machine learning community, there are only a few studies examining the theoretical justification of this learning framework. The focus of previous studies is on providing learning guarantees in the form of generalization error bounds. The study of generalization bounds is considered as an important problem in machine learning, and, more specifically, in statistical learning theory. This importance is twofold: (1) generalization bounds provide an upper-tail confidence interval for the true risk of a learning algorithm the latter of which cannot be precisely calculated due to its dependency to some unknown distribution P from which the data are drawn, (2) this type of bounds can also be employed as model selection tools, which lead to identifying more accurate learning models. The generalization error bounds are typically expressed in terms of the empirical risk of the learning hypothesis along with a complexity measure of that hypothesis. Although different complexity measures can be used in deriving error bounds, Rademacher complexity has received considerable attention in recent years, due to its superiority to other complexity measures. In fact, Rademacher complexity can potentially lead to tighter error bounds compared to the ones obtained by other complexity measures. However, one shortcoming of the general notion of Rademacher complexity is that it provides a global complexity estimate of the learning hypothesis space, which does not take into consideration the fact that learning algorithms, by design, select functions belonging to a more favorable subset of this space and, therefore, they yield better performing models than the worst case. To overcome the limitation of global Rademacher complexity, a more nuanced notion of Rademacher complexity, the so-called local Rademacher complexity, has been considered, which leads to sharper learning bounds, and as such, compared to its global counterpart, guarantees faster convergence rates in terms of number of samples. Also, considering the fact that locally-derived bounds are expected to be tighter than globally-derived ones, they can motivate better (more accurate) model selection algorithms.While the previous MTL studies provide generalization bounds based on some other complexity measures, in this dissertation, we prove excess risk bounds for some popular kernel-based MTL hypothesis spaces based on the Local Rademacher Complexity (LRC) of those hypotheses. We show that these local bounds have faster convergence rates compared to the previous Global Rademacher Complexity (GRC)-based bounds. We then use our LRC-based MTL bounds to design a new kernel-based MTL model, which enjoys strong learning guarantees. Moreover, we develop an optimization algorithm to solve our new MTL formulation. Finally, we run simulations on experimental data that compare our MTL model to some classical Multi-Task Multiple Kernel Learning (MT-MKL) models designed based on the GRCs. Since the local Rademacher complexities are expected to be tighter than the global ones, our new model is also expected to exhibit better performance compared to the GRC-based models.
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Date Issued
2017
Identifier
CFE0006827, ucf:51778
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006827