Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 74-80).

Thesis (M.A.)--York University, 2008. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 72-94). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR45951

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

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A tridimensional optical display is described which is capable of producing real images with no optics between the observer and the image. This display, which is called the Visually Integrated Volumetric Image (VIVID), was developed as a laboratory system designed to be used in vision research. Three dimensional Lissajous patterns were produced, whose rotational position and axial depth could be precisely controlled by a general purpose digital minicomputer. By reversing the direction of rotation of the pattern in a known manner, and recording a subject's ability to perceive the true rotational direction for various amounts of axial image depth, the transition between the kinetic depth effect and true depth perception could be investigated. This transition forms the basis for defining a depth perception threshold for this type of a dynamic three dimensional image. Two experiments were performed using this approach. In the first experiment, ten undergraduate and graduate students (both male and female) observed the pattern during 24 one-minute trials. Eight different axial depth values were used, with three trials at each depth. The patterns were made to reverse rotation direction in a pseudo-random manner which was different for each trial presented to a given subject. The subject indicated the perceived direction of rotation by controlling a two position rotary switch, which was monitored by the computer. The total time during which the subject correctly tracked the rotation was integrated by the computer. The ratio of this correct tracking time to the total trial time was taken as a measure of the subject's ability to perceive the axial depth of the image. Plots of this ratio as a function of image depth are presented and discussed. The results averaged over all subjects produce a remarkably smooth curve, yielding a depth perception threshold of 2 mm for the subject population under the given experimental conditions. The characteristics of the stimulus were: (a) 2 cm high by 2 cm wide pattern; (b) Lissajous pattern frequency ratio of 6:1; (c) Axial distance from observer of 55 cm; (d) Wavelength of 533 nm (green); (e) Horizontal rotation axis; (f) Rotation period of 7 seconds; (g) Neutral background field illumination over a 40° come angle; (h) Image line width of 0.5 mm. The second experiment was a pilot experiment designed to investigate the effect of wavelength variations on this form of depth perception. A single subject was presented with a total of 192 one-minute trials at four wavelengths spanning the visible region (i.e., 6 one-minute trials for each of eight depth values at each wavelength). No significant wavelength dependence was observed in this pilot experiment.

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This dissertation used letter detection and masked priming to address four questions: Are graphemes or letters more fundamental in low-level reading processes? How does alphabetic-processing knowledge manifest in different languages? Do bilinguals transfer such knowledge across languages? And do young children also show such effects?Some researchers have recently revived an old hypothesis in which graphemes, not letters, are the fundamental, perceptual reading unit. This can be tested by looking at congruency effects in a letter-detection task with masked priming. Six groups participated: Spanish and English monolingual adults; Spanish- and English-dominant bilingual adults; Spanish-dominant bilingual children; and English monolingual children. The experiments with adult monolinguals tested the letter- against the grapheme-as-percept hypothesis. The experiments with developing bilinguals examined whether they would transfer alphabetic-processing knowledge from L1 to L2. And the experiments with English monolingual children probed how early congruency effects with masked primes might occur.Participants responded YES or NO depending on the presence of letters in targets. Both congruent and incongruent masked primes preceded the targets. Among the congruent primes, some contained double vowels, and others single vowels. Assuming letters are fundamental, single- and double-vowel primes in both languages should facilitate and inhibit reactions equally. Assuming graphemes are fundamental, single-vowel primes in English, but not Spanish, should facilitate and inhibit more because double vowels are digraphs in English, and should therefore conceal the identity of their component letters. Bilinguals should show L1-like effects in L2 if they transfer alphabet-specific processing knowledge. Young children should simply show congruency effects if they are able to process letter information automatically.The results with Spanish and English monolinguals suggested that graphemes do exert an effect on the task, but only after letters are perceived. This has major implications for models of proficient reading. The results also suggest that Spanish readers do not construct graphemes from letters, but rather syllables and abstract syllable structure. Bilinguals showed evidence of L1-L2 transfer at low levels of L2 proficiency. This has implications for transitional bilingual education programs. And young children showed congruency effects, which provides another link in establishing the connection between literacy development and proficient reading.