Thesis (Ph. D.)--University of Oregon, 2008. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 147-151). Also available online in ProQuest, free to University of Oregon users.

abstract: Contemporary online social platforms present individuals with social signals in the form of news feed on their peers' activities. On networks such as Facebook, Quora, network operator decides how that information is shown to an individual. Then the user, with her own interests and resource constraints selectively acts on a subset of items presented to her. The network operator again, shows that activity to a selection of peers, and thus creating a behavioral loop. That mechanism of interaction and information flow raises some very interesting questions such as: can network operator design social signals to promote a particular activity like sustainability, public health care awareness, or to promote a specific product? The focus of my thesis is to answer that question. In this thesis, I develop a framework to personalize social signals for users to guide their activities on an online platform. As the result, we gradually nudge the activity distribution on the platform from the initial distribution p to the target distribution q. My work is particularly applicable to guiding collaborations, guiding collective actions, and online advertising. In particular, I first propose a probabilistic model on how users behave and how information flows on the platform. The main part of this thesis after that discusses the Influence Individuals through Social Signals (IISS) framework. IISS consists of four main components: (1) Learner: it learns users' interests and characteristics from their historical activities using Bayesian model, (2) Calculator: it uses gradient descent method to compute the intermediate activity distributions, (3) Selector: it selects users who can be influenced to adopt or drop specific activities, (4) Designer: it personalizes social signals for each user. I evaluate the performance of IISS framework by simulation on several network topologies such as preferential attachment, small world, and random. I show that the framework gradually nudges users' activities to approach the target distribution. I use both simulation and mathematical method to analyse convergence properties such as how fast and how close we can approach the target distribution. When the number of activities is 3, I show that for about 45% of target distributions, we can achieve KL-divergence as low as 0.05. But for some other distributions KL-divergence can be as large as 0.5. / Dissertation/Thesis / M.S. Computer Science 2014

This study addresses an individual's performance, relating it to eyesight changes due to the aging of the individual and to color computer screens used for computer-based-instruction not designed specifically for older students. This study determines how existing research in gerontology, human-computer interface, and color use in visual graphics can be applied to the design of computer screen displays containing color text and backgrounds and how various color combinations will affect performance by adult learners forty years of age and older. The results of this research provide software developers and instructional designers guidelines to use when designing computer screen displays for use in instructional computing settings involving older adults.

Humans are very effective at evaluating information visually. Scientific visualization is concerned with the process of presenting complex data in visual form to exploit this capability. A large array of tools is currently available for visual presentation. This research attempts to evaluate the effectiveness of three different presentation models that could be used for scientific visualization. The presentation models studied were, two-dimensional perspective rendering, field sequential stereoscopic three dimensional rendering and immersive virtual reality rendering. A large section of a three dimensional sub surface seismic survey was modeled as four-dimensional data by including a value for seismic reflectivity at each point in the survey. An artificial structure was randomly inserted into this data model and subjects were asked to locate and identify the structures. A group of seventeen volunteers from the University of Houston student body served as subjects for the study. Detection time, discrimination time and discrimination accuracy were recorded. The results showed large inter subject variation in presentation model preference. In addition the data suggest a possible gender effect. Female subjects had better overall performance on the task as well as better task acquisition.

In this dissertation, I investigate the value of information to consumers, the pricing of chicken, and the value of shopping lists to consumers. My first essay finds that across 14 different product categories and seven types of information, information about price and origin are the most important and information about social and environmental impacts are the least important. Our estimates also suggest consumers are willing to wait a large amount of time to obtain the most vs. least desirable types of information prior to making a non-hypothetical product choice. My second essay relates to price indices used to value chicken in the United States. There were two main price indices commonly used by the industry in recent history: the USDA 12-City Price Index and the Georgia Dock Price. We find that there was a long standing equilibrium relationship between these two price indices that shifted across time. Additionally, our analysis shows that there was a structural break between these two price indices around 2000. After this structural break, the analysis suggests Georgia Dock prices were about $0.047/lb higher than they would have been without the break. Last, my third essay aims to determine the impact of shopping lists on consumer spending and healthy shopping behaviors. We find that after controlling for conscientiousness, consumers willingness-to-accept to give up their shopping list is $5.05, while the equivalent gain to write a shopping list is $3.87. We did not find a significant difference in the healthiness of the purchases made by consumers using a shopping list versus those who shopped without a list.

This dissertation examines those attributes of full-color display systems (particularly color matrix displays) which degrade image quality. Based on this analysis, it is suggested that a comprehensive metric should measure image quality in terms of transmitted signal and noise modulation, both achromatic and chromatic. Moreover, it is suggested that these signal and noise measurements be weighted in terms of human spatial-chromatic visual characteristics. A review of extant image quality metrics reveals several limitations of these metrics which make them unsuitable for the evaluation of color matrix displays. These limitations include the inability to account for chromatic modulation transfer and chromatic noise as well as the general inability to account for spatial and grey-scale sampling. This work describes a new methodology for assessing image quality that can be applied to full-color as well as monochromatic, and sampled as well as continuous, display systems. Unlike most display quality metrics, the proposed methodology is not based on the tools of linear systems analysis. Rather, it is based on more veridical models of the human visual system (HVS), including multi-channel models of spatial vision, the zone theory of color vision, physiological models of retinal processes, and models of the optics of the eye. A display evaluation system consisting of the HVS model used in conjunction with a display simulator is described. The HVS model employs nine image processing stages to account for nonlinear retinal processes, opponent color encoding, and multiple spatial frequency channels. A detailed procedure for using the HVS model to evaluate display systems is provided. The validity of the HVS model was tested by conducting contrast detection, discrimination, and magnitude estimation experiments on the model. The results of these experiments correspond closely with published human performance data The utility of the display evaluation system was assessed by making image quality predictions for the display systems used in three image quality studies. Image quality predictions using the proposed system correlate strongly with ratings of image quality provided by human subjects. Results of these validation studies indicate that the proposed method of display evaluation is viable and warrants further development. / Ph. D.

The primary objective of this dissertation was to investigate the effects of varying levels of luminance, color, and spatial frequency content on the perceived image quality of a soft-copy color image. A secondary objective was to test the robustness of selected image quality metrics (MTFA, SQRI, and ICS) to the color variations as measured by the change in correlations between the perceived quality ratings and the values of the image quality metrics. To accomplish these objectives, a color image was selected and its luminance, color, and spatial frequency components were attenuated systematically using image processing software. With the manipulated images, an experiment was conducted in which subjects were asked to rate, on a 0.0 - 9.0 continuous scale, the perceived quality of a displayed image in comparison to the original image. Results of the statistical analysis of the collected data were characterized by the highly significant main effects and interaction effects. However, the magnitudes of the interactions were small. The effect of the luminance component on perceived quality was found to be dominant and consistent across all the levels of the other two variables. As the luminance increased, the perceived quality increased at a decreasing rate. The luminance main effect was modeled well (R² = 0.9968) by the second-order polynomial of the luminance attenuation level, or, equivalently, by the relative amount of the luminance contained in the image. The range of variation of perceived quality produced by the six luminance levels was about five units on a 0.0 - 9.0 continuous scale. It was concluded that perceived quality of the color image was determined primarily by the luminance component of the image. The effect of color on perceived quality was found to be smaller than expected. The range of variation in perceived quality produced by the six color levels was only a little over one unit on a 0.0 - 9.0 continuous scale. Perceived qualities increased at a decreasing rate as the level of color increased. However, the slope of the curve representing the color effect was smaller than that of the luminance effect The main effect of color was modeled well (R² = 0.9972) by the second-order polynomial of the color attenuation level, or, equivalently, by the relative amount of color contained in the image. Based on the findings of the color effect, two different roles of color in image perception are suggested. At extremely low luminance, color acts primarily as a facilitator of the luminance by providing more cues on the content of the image. At sufficiently high luminance, the increased perceived quality stems from the aesthetic characteristics of the color. Both highpass and lowpass filtering, on the average, caused about 1.5 units of degradation as compared to the unfiltered image in perceived image quality on a 0.0 - 9.0 continuous scale. The perceived quality of the unfiltered image was greater than that of the filtered images across all the levels of luminance and color attenuation except at a low luminance level. There was no significant difference between the perceived qualities of the highpass and lowpass filtered images. The R² of the second-order polynomial for image qUality metrics (MTFA, SQRI, and ICS) and the mean perceived qualities did not vary across the color variations in the image manipulations. That is, these image quality metrics were robust to the color variations when the relationship between the quality metric values and the actual perceived qualities was represented by the second-order polynomial. However, with the first-order model, the R² increased as the color level increased. The SQRI yielded higher R² values than did the MTFA and ICS metrics when the first-order model was used. Also, the range of variation of R² for the SQRI was smaller than that for the other two metrics. Therefore, it appears that the robustness of an image quality metric to the color variation is affected by the degree of non-linearity correction in the metric if the robustness is tested in the context of the straight-line relationship. / Ph. D.

A two-phase study was conducted which related the confusions I among dot matrix characters to the two-dimensional spatial frequency similarity of these characters. During the first phase of the study, subjects were shown single alphanumeric characters from four different dot matrix fonts. In addition to the font variable, the size of the character was varied. All common matrix sizes, 5 X 7, 7 X 9, and 9 X 11, were used. The design of the study allowed the effects of matrix size (number of dots) and character size (angular subtense) to be separated in the analysis. Data from this phase of the research were analyzed in terms of both correctness and character confusion frequencies. The ANOVA of the number of correct character recognitions provided interesting interaction effects among font and matrix/character size. These results are discussed in terms of display design considerations. The second phase of the study consisted of digitizing and analyzing all characters from two of the fonts used in the first phase. The fonts chosen represent the most and least confusable of the four, based on the performance data obtained. These characters were scanned photometrically using a computer-controlled X-Y stage. The resultant digitized arrays were subjected to a 512 X 512 point fast Fourier transform (FFT). The Fourier coefficients were correlated for all possible character pairs within each font-matrix/character size cell. These correlations provided an objective similarity measure among characters based upon their 2-D spatial frequency spectra. In addition to the spatial frequency similarity measure, a simple digital Phi coefficient was calculated for each character pair. This coefficient is simply a nonparametric correlation coefficient between two digital arrays. The final analysis performed in this study was the correlation of observed performance (confusions) with objective similarity measures (2-D spectra and Phi coefficients). A strong relationship between objective and subjective confusability would be a very useful design aid for display manufacturers. The obtained correlational relationships are discussed in terms of their utility for design and their implications for visual system models based on spatial frequency analysis. / Ph. D.

An important problem for the human factors specialist involves specifying the extent to which the quality of a displayed image will affect observer performance. One approach to this problem has been to develop metrics of image quality and to correlate measured image quality with observer performance. Of the metrics that have been developed, the Modulation Transfer Factor Area (MTFA) has proven to be a useful predictor of observer performance. The MTFA metric takes into account the system's Modulation Transfer Function and observer threshold curves. Two experiments were performed to assess the effects of the quality of a televised image on eye movements and search-related dependent measures. The first experiment search task involved having subjects perform an air-to-ground search during simulated flight. The quality of the image presented was varied by either passing, low-pass filtering, or attenuating the video signal and by adding electrical white noise to the video signal. The results of this experiment indicate that (1) at the highest level of electrical noise added, the percent of correct target acquisitions was decreased moderately, (2) the larger the target, the higher the percent correct responses, (3) the low-pass filtering of the video signal led to shorter ground ranges at acquisition for the large-sized targets, and (4) that the larger the target, the longer the fixation duration. Low to moderate correlations between MTFA and performance measures generally indicated that as MTFA increases performance improves, and that as MTFA increases fixation duration decreases. The search task of the second experiment consisted of having the subjects search for a designated letter or numeral across a televised picture of randomly positioned letters and numerals. The quality of the picture was varied by either passing, low-pass filtering, high-pass filtering, or attenuating the video signal and by adding electrical white noise to the video signal. The results of this experiment indicated that (1) the high-pass filtered high noise level condition led to significantly longer search times; and (2) the fixation times associated with the high-pass filtered condition were longer than those associated with the low-pass filtered, at- tenuated, and unfiltered unattenuated conditions, and that this effect was most pronounced under high noise level conditions. Correlations between MTFA and performance measures indicated that increases in MTFA lead to decreases in search time and decreases in fixation duration. The results of tests among fixation and saccade duration distribution across both experiments consistently showed significant individual differences and non-normality. Examination of pooled fixation duration distributions showed large dispersion differences across the static and dynamic imagery experiments. This result, and the differences of pooled fixation and saccade duration distribution ranges do not support the search model assumption of constant glimpse durations and reveal serious.flaws in the structure of search models. / Ph. D.

M. S.