Matching Items (10)
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- Genre: Masters Thesis
- Creators: Arizona State University
- Creators: Chakraborty, Bijeta
- Member of: ASU Electronic Theses and Dissertations
Description
Frequency effects favoring high print-frequency words have been observed in frequency judgment memory tasks. Healthy young adults performed frequency judgment tasks; one group performed a single task while another group did the same task while alternating their attention to a secondary task (mathematical equations). Performance was assessed by correct and error responses, reaction times, and accuracy. Accuracy and reaction times were analyzed in terms of memory load (task condition), number of repetitions, effect of high vs. low print-frequency, and correlations with working memory span. Multinomial tree analyses were also completed to investigate source vs. item memory and revealed a mirror effect in episodic memory experiments (source memory), but a frequency advantage in span tasks (item memory). Interestingly enough, we did not observe an advantage for high working memory span individuals in frequency judgments, even when participants split their attention during the dual task (similar to a complex span task). However, we concluded that both the amount of attentional resources allocated and prior experience with an item affect how it is stored in memory.
ContributorsPeterson, Megan Paige (Author) / Azuma, Tamiko (Thesis advisor) / Gray, Shelley (Committee member) / Liss, Julie (Committee member) / Arizona State University (Publisher)
Created2013
Description
Efficiency of components is an ever increasing area of importance to portable applications, where a finite battery means finite operating time. Higher efficiency devices need to be designed that don't compromise on the performance that the consumer has come to expect. Class D amplifiers deliver on the goal of increased efficiency, but at the cost of distortion. Class AB amplifiers have low efficiency, but high linearity. By modulating the supply voltage of a Class AB amplifier to make a Class H amplifier, the efficiency can increase while still maintaining the Class AB level of linearity. A 92dB Power Supply Rejection Ratio (PSRR) Class AB amplifier and a Class H amplifier were designed in a 0.24um process for portable audio applications. Using a multiphase buck converter increased the efficiency of the Class H amplifier while still maintaining a fast response time to respond to audio frequencies. The Class H amplifier had an efficiency above the Class AB amplifier by 5-7% from 5-30mW of output power without affecting the total harmonic distortion (THD) at the design specifications. The Class H amplifier design met all design specifications and showed performance comparable to the designed Class AB amplifier across 1kHz-20kHz and 0.01mW-30mW. The Class H design was able to output 30mW into 16Ohms without any increase in THD. This design shows that Class H amplifiers merit more research into their potential for increasing efficiency of audio amplifiers and that even simple designs can give significant increases in efficiency without compromising linearity.
ContributorsPeterson, Cory (Author) / Bakkaloglu, Bertan (Thesis advisor) / Barnaby, Hugh (Committee member) / Kiaei, Sayfe (Committee member) / Arizona State University (Publisher)
Created2013
Description
Although there are many forms of organization on the Web, one of the most prominent ways to organize web content and websites are tags. Tags are keywords or terms that are assigned to a specific piece of content in order to help users understand the common relationships between pieces of content. Tags can either be assigned by an algorithm, the author, or the community. These tags can also be organized into tag clouds, which are visual representations of the structure and organization contained implicitly within these tags. Importantly, little is known on how we use these different tagging structures to understand the content and structure of a given site. This project examines 2 different characteristics of tagging structures: font size and spatial orientation. In order to examine how these different characteristics might interact with individual differences in attentional control, a measure of working memory capacity (WMC) was included. The results showed that spatial relationships affect how well users understand the structure of a website. WMC was not shown to have any significant effect; neither was varying the font size. These results should better inform how tags and tag clouds are used on the Web, and also provide an estimation of what properties to include when designing and implementing a tag cloud on a website.
ContributorsBanas, Steven (Author) / Sanchez, Christopher A (Thesis advisor) / Branaghan, Russell (Committee member) / Cooke, Nancy J. (Committee member) / Arizona State University (Publisher)
Created2011
Description
Class D Amplifiers are widely used in portable systems such as mobile phones to achieve high efficiency. The demands of portable electronics for low power consumption to extend battery life and reduce heat dissipation mandate efficient, high-performance audio amplifiers. The high efficiency of Class D amplifiers (CDAs) makes them particularly attractive for portable applications. The Digital class D amplifier is an interesting solution to increase the efficiency of embedded systems. However, this solution is not good enough in terms of PWM stage linearity and power supply rejection. An efficient control is needed to correct the error sources in order to get a high fidelity sound quality in the whole audio range of frequencies. A fundamental analysis on various error sources due to non idealities in the power stage have been discussed here with key focus on Power supply perturbations driving the Power stage of a Class D Audio Amplifier. Two types of closed loop Digital Class D architecture for PSRR improvement have been proposed and modeled. Double sided uniform sampling modulation has been used. One of the architecture uses feedback around the power stage and the second architecture uses feedback into digital domain. Simulation & experimental results confirm that the closed loop PSRR & PS-IMD improve by around 30-40 dB and 25 dB respectively.
ContributorsChakraborty, Bijeta (Author) / Bakkaloglu, Bertan (Thesis advisor) / Garrity, Douglas (Committee member) / Ozev, Sule (Committee member) / Arizona State University (Publisher)
Created2012
Description
There have been conflicting accounts of animation's facilitation in learning from instructional media, being at best no different if not hindering performance. Procedural motor learning represents one of the few the areas in which animations have shown to be facilitative. These studies examine the effects of instructional media (animation vs. static), rotation (facing vs. over the shoulder) and spatial abilities (low vs. high spatial abilities) on two procedural motor tasks, knot tying and endoscope reprocessing. Results indicate that for all conditions observed in which participants engaged in procedural motor learning tasks, performance was significantly improved with animations over static images. Further, performance was greater for rotations of instructional media that did not require participants to perform a mental rotation under some circumstances. Interactions between Media x Rotation suggest that media that was animated and did not require a participant to mentally rotate led to improved performance. Individual spatial abilities were found to influence total steps correct and total number of errors made in the knot tying task, but this was not observed in the endoscope task. These findings have implications for the design of instructional media for procedural motor tasks and provide strong support for the usage of animations in this context.
ContributorsGarland, T. B (Author) / Sanchez, Chris A (Thesis advisor) / Cooke, Nancy J. (Committee member) / Branaghan, Russel (Committee member) / Arizona State University (Publisher)
Created2012
Description
Individual differences in working memory capacity partly arise from variability in attention control, a process influenced by negative emotional content. Thus, individual differences in working memory capacity should be predictive of differences in the ability to regulate attention in emotional contexts. To address this hypothesis, a complex-span working memory task (symmetry span) was modified so that negative arousing images or neutral images subtended the background during the encoding phase. Across three experiments, negative arousing images impaired working memory encoding relative to neutral images, resulting in impoverished symmetry span scores. Additionally, in Experiment 3, both negative and arousing images captured attention and led to increased hit rates in a subsequent recognition task. Contrary to the primary hypothesis, individual differences in working memory capacity derived from three complex span tasks failed to moderate the effect of negative arousing images on working memory encoding across two large scale studies. Implications for theories of working memory and attention control in emotional contexts will be discussed.
ContributorsWingert, Kimberly Marie (Author) / Brewer, Gene A. (Thesis advisor) / Amazeen, Eric (Committee member) / Killeen, Peter (Committee member) / Goldinger, Stephen (Committee member) / Arizona State University (Publisher)
Created2015
Description
Social gaze-following consists of both reflexive and volitional control mechanisms of saccades, similar to those evaluated in the antisaccade task. This similarity makes gaze-following an ideal medium for studying attention in a social context. The present study seeks to utilize reflexive gaze-following to develop a social paradigm for measuring attention control. Two gaze-following variations of the antisaccade task are evaluated. In version one, participants are cued with still images of a social partner looking either left or right. In version two, participants are cued with videos of a social partner shifting their gaze to the left or right. As with the traditional antisaccade task, participants are required to look in the opposite direction of the target stimuli (i.e., gaze cues). Performance on the new gaze-following antisaccade tasks is compared to the traditional antisaccade task as well as the highly related ability of working memory.
ContributorsYonehiro, Jade Noelani Lee (Author) / Duran, Nicholas D (Thesis advisor) / Burleson, Mary H (Committee member) / Horne, Zachary (Committee member) / Arizona State University (Publisher)
Created2018
Description
In this thesis, a digital input class D audio amplifier system which has the ability
to reject the power supply noise and nonlinearly of the output stage is presented. The main digital class D feed-forward path is using the fully-digital sigma-delta PWM open loop topology. Feedback loop is used to suppress the power supply noise and harmonic distortions. The design is using global foundry 0.18um technology.
Based on simulation, the power supply rejection at 200Hz is about -49dB with
81dB dynamic range and -70dB THD+N. The full scale output power can reach as high as 27mW and still keep minimum -68dB THD+N. The system efficiency at full scale is about 82%.
to reject the power supply noise and nonlinearly of the output stage is presented. The main digital class D feed-forward path is using the fully-digital sigma-delta PWM open loop topology. Feedback loop is used to suppress the power supply noise and harmonic distortions. The design is using global foundry 0.18um technology.
Based on simulation, the power supply rejection at 200Hz is about -49dB with
81dB dynamic range and -70dB THD+N. The full scale output power can reach as high as 27mW and still keep minimum -68dB THD+N. The system efficiency at full scale is about 82%.
ContributorsBai, Jing (Author) / Bakkaloglu, Bertan (Thesis advisor) / Arizona State University (Publisher)
Created2015
Description
Behavioral, electrophysiological, and neuroimaging evidence has demonstrated that multiple object tracking (MOT) tasks draw upon visual perception, attention, and working memory cognitive processes. Functional neuroimaging studies identified the middle temporal visual area (MT+/V5) as one of several brain regions associated with MOT in humans. MT+/V5 is thought to be responsible for processing motion from visual information, regulating smooth pursuit eye movements, and encoding memory for motion. However, it is unclear how MT+/V5 interacts with attention and working memory performance processes during MOT. To investigate this question, the right MT+/V5 region was identified in 14 neurotypical subjects using structural magnetic resonance imaging (sMRI). The right MT+/V5 was stimulated using intermittent theta-burst stimulation (iTBS), continuous theta-burst stimulation (cTBS), and sham transcranial magnetic stimulation (TMS) using a within-subjects design. Average MOT performance was measured before and 5-min, 30-min, and 60-min after each stimulation protocol. There was no significant difference in average MOT performance across time, regardless of the stimulation condition.
ContributorsAlucard, Myles (Author) / Duran, Nicholas (Thesis advisor, Committee member) / Brewer, Gene (Thesis advisor, Committee member) / Burleson, Mary (Committee member) / Arizona State University (Publisher)
Created2023
Description
Statistical word learning (SWL) has been proposed and tested as a powerful mechanism for word learning under referential ambiguity. Learners are adept at resolving word-referent ambiguity by calculating the co-occurrences between words and referents across ambiguous scenes. Despite the generalizability of such capacity, it is less clear which underlying factors may play a role in SWL, such as learners’ language experience and individual differences of working memory. The current study therefore asked two questions: 1) How do learners of different language experience (monolinguals and bilinguals) approach SWL of different mapping types–when each referent has one name (1:1 mapping) or two names (2:1 mapping)? and 2) How do working memory capacities (spatial and phonological) play a role in SWL by mapping type? In this pre-registered study (OSF: https://osf.io/mte8s/), 69 English monolinguals and 88 bilinguals completed two SWL tasks (1:1 and 2:1 mapping), a symmetry span task indexing spatial working memory, and a listening span task indexing phonological working memory. Results showed no differences between monolinguals and bilinguals in SWL of both mapping types. However, spatial and phonological working memory positively predicted SWL regardless of language experience, but only in 1:1 mapping. The findings show a dissociation of working memory’s role in SWL of different mapping types. The study proposes a novel insight into a theoretical debate underlying statistical learning mechanisms: learners may adopt more explicit processes (i.e. hypothesis-testing) during 1:1 mapping but implicit processes (i.e. associative learning) during 2:1 mapping. Future studies can locate memory-related brain areas during SWL to test out the proposal.
ContributorsLi, Ye (Author) / Benitez, Viridiana (Thesis advisor) / Goldinger, Stephen (Committee member) / Brewer, Gene (Committee member) / Arizona State University (Publisher)
Created2022