Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 17, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Nelson Cowan. Includes bibliographical references.

Thesis (D. Min.)--Columbia International University, 2007. / Typescript. "December, 2007." Also available in CD-ROM. Description based on print version record. Includes bibliographical references (leaves 166-173).

published_or_final_version / Psychology / Master / Master of Philosophy

Visual working memory (VWM) has long been considered to be limited in capacity, but the way in which it is limited remains unclear. One of the theoretical debates in visual working memory concerns whether the number of objects that can be stored is fixed (discrete slot models) or variable (flexible resource models). Recent research on the resolution of VWM has helped elucidate this debate by acknowledging an important trade-off between number and resolution: as the number of items stored increases, the resolution of representation declines. Yet, a different conception suggests that the number and resolution may represent distinct aspects of visual working memory, evidenced by both behavioral and neuroimaging data. In this thesis, I examined three theoretical questions regarding the relationship between the number and the resolution of items in VWM. First, how does set size affect high- & low-resolution representations (differentially)? If an item limit can be evidenced in the high-resolution measure, but not in the low-resolution measure, my second research question emerges. That is, how much resolution do we have for the remaining objects when the item limit is exceeded? Third, if both high- & low-resolution representations of an item exist in VWM, are they stored together or independently? In a series of five experiments, I addressed these questions using an adapted continuous report paradigm, in which participants were asked to remember a mixture of objects from two categories and respond firstly to the category of the item-to-report (low-resolution measure), followed by a second within-category response (high-resolution measure) which was contingent on the first. In Experiments 1-2, only performance in the low-resolution, but not in the high-resolution, measure was largely indifferent to set size, which was not compatible with either discrete slot or flexible resource models, but was largely consistent with predictions from the two-factor model and the neural object-file theory. In Experiments 3-4, precision of high-resolution representations declined monotonically until the set size reached around four items, fitting to the predictions from discrete slot models. The overall accuracy in low-resolution measure, however, remained relatively high, suggesting differential set size influence on high- and low-resolution representations. In Experiment 5, capacity comparison revealed no significant difference when the low-resolution task was absent. Taken together, I demonstrate that 1) both low-resolution ensemble representations and high-resolution individual item representations exist in VWM, and 2) high-resolution representations (i.e. object identity) and low-resolution representations (i.e. objects’ categories, configural information and perhaps some coarse feature information) of an object might be stored independently. / published_or_final_version / Psychology / Master / Master of Philosophy

In older children and adults, words are stored in the mental lexicon in an organized manner and processed in a systematic manner on the basis of their phonological structures. The processing of novel words is therefore more efficient. Young children may process a novel word in a holistic manner, and the words are not stored phonemically distinct with one another in the mental lexicon. Priming is a method often used in spoken word recognition studies. The effects of phonological primes on word learning would reflect the organization of mental lexicon in young children. At the same time, research has shown that there is a positive correlation between phonological short-term memory (STM) and word learning. But the mechanism of how both phonological STM and mental lexicon are involved in word learning is not clear. Forty-two five- to seven-years-old children with a mean age of 6;06 (SD = 0;10) participated in a spoken word learning task. They were presented with names of 18 novel cartoon characters in nine word learning blocks and the names were novel disyllables that are consistent with the phonotactics of Cantonese. In each block, children were exposed to two novel words along with two real words as primes, with the primes phonologically similar to one novel word (“PHONOLOGICAL” condition) but not with the other one (“UNRELATED” condition). They heard each novel word twice and the primes three times. These participants also took part in nonword repetition tasks and a serial order construction task as measures of the phonological STM. A significantly positive effect of phonological priming was observed in the cartoon character naming but not in the form identification and the referent identification. Further analysis of the naming results showed that only the same-onset-and-tone primes produced a significant priming effect. Among the various short-term memory measures, only nonword repetition of pseudosyllables (syllable score) was significantly and positively correlated with the cartoon character naming score after controlling for age. The findings of the present study presented some evidence that even five-year-old Cantonese-speaking children have already organized the lexical representations in neighbourhoods so that phonological primes could exert facilitatory effects on their spoken word learning. Even this young group of children was able to process novel words in a segmental manner. But there could still be some subtle differences between the younger and older children. A word learning model which integrates the involvement of phonological STM and mental lexicon could help to explain how these two memory components contribute to word learning and the word learning differences between the younger and older children. The preliminary findings of this study provided some evidence in children’s sensitivity to the phonological structures of novel spoken words. Cantonese-speaking children, similar to English-speaking ones, are sensitive to the phonological structures of novel words and phonological primes facilitate their spoken word learning. The results of this study further suggest long-term memory and phonological short-term memory are involved at the initial stage of word learning. However, the mechanism of interactions needs to be further investigated. / published_or_final_version / Speech and Hearing Sciences / Master / Master of Philosophy

Accurate short term load forecasting plays a very important role in power system management. As electrical load data is highly non-linear in nature, in the proposed approach, we first separate out the linear and the non-linear parts, and then forecast the load using the non-linear part only. The Semiparametric spectral estimation method is used to decompose a load data signal into a harmonic linear signal model and a nonlinear trend. A support vector machine is then used to predict the non-linear trend. The final predicted signal is then found by adding the support vector machine predicted trend and the linear signal part. With careful determination of the linear component, the performance of the proposed method seems to be more robust than using only the raw load data, and in many cases the predicted signal of the proposed method is more accurate when we have only a small training set.

published_or_final_version / abstract / Linguistics / Master / Master of Arts

No description available.

The activity of neurons in the prefrontal cortex (PFC) may underlie working memory processes in the brain. Both the performance of working memory tasks and the activity of PFC neurons are modulated by dopamine. The goal of the present thesis was to gain insight into the neural basis of working memory by studying the PFC, and the DA system in the PFC, from both a behavioral and cellular perspective. The functional contribution of the PFC to working memory processes in the rat was assessed in Chapter 2 of the present thesis using memory-based foraging tasks on an 8-arm radial maze. The results of these studies indicated that lidocaine-induced inactivations of the PFC selectively disrupted the ability to use mnemonic information to guide foraging, but not the ability to acquire or retain such information. The ability to use mnemonic information to guide foraging was also disrupted by microinjection of a D1 but not D2 receptor antagonist into the PFC. Chapters 3-5 investigated how PFC neurons process synaptic inputs to their dendrites to produce spike output. The intrinsic membrane properties and synaptic responses at the soma and dendrites of deep layer PFC pyramidal neurons were recorded using sharp intracellular or whole-cell patch-clamp techniques in a brain-slice preparation. Different passive and active membrane properties of the soma and dendrites of PFC neurons were observed. The distal dendrites of PFC neurons responded most effectively to strong, highly coincident synaptic inputs. Ca²⁺currents near the soma both amplified the effects of these inputs and modulated the spike output pattern. Spike output at the soma was also controlled by the interplay of slowly-inactivating Na⁺ and K⁺ currents. Chapter 6 investigated the modulation of PFC neurons by DA. DA or a D1 but not D2 receptor agonist increased the evoked firing of PFC neurons via a D1- mediated modulation of slowly-inactivating Na⁺ and K⁺ currents. Concurrently, D1 receptor activation reduced burst firing in PFC neurons, due to a attenuation of Ca²⁺ currents. D1 receptor activation also increased both GABA[sub A] IPSPs and NMDA EPSPs. The final chapter of this thesis integrated these data into a cellular model of PFC function and its modulation by DA. It is proposed that DA may tune PFC neurons such that they respond selectively to strong synchronized inputs from other cortical areas. In the presence of DA, working memory processes mediated by the PFC may be influenced selectively by stimuli of behavioral significance.

No description available.