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Prior research has explored the counterchange model of motion detection in terms of counterchanging information that originates in the stimulus foreground (or objects). These experiments explore counterchange apparent motion with regard to a new apparent motion stimulus where the necessary counterchanging information required for apparent motion is provided by altering the luminance of the background. It was found that apparent motion produced by background-counterchange requires longer frame durations and lower levels of average stimulus contrast compared to foreground-counterchange. Furthermore, inter-object distance does not influence apparent motion produced by background-counterchange to the degree it influences apparent motion produced by foreground-counterchange. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

Teleost retinal ganglion cells can regenerate severed axons following injury, something their mammalian counterparts cannot do. In the teleost, successful regeneration has been attributed in part to microglial cell activities including the phagocytosis of myelin. Although the regulation of microglial phagocytosis has been studied in mammals, in the teleost it is largely unexamined. The present study was designed to identify mediators of microglial phagocytosis released by injured goldfish optic nerve during the course of regeneration. We found that microglial phagocytosis was significantly enhanced in the presence of a 7 day regenerating nerve or medium conditioned by the nerve (CM). When either nerve or CM was incubated with microglia along with an antibody against tumour necrosis factor alpha (TNFalpha), this effect was neutralized. The L929 cell cytotoxicity assay further demonstrated TNFalpha activity in the CM. However, Western blot analysis did not confirm this result. Therefore, further work is necessary to clearly establish the presence of TNFalpha.

Thesis (Ph.D.)--University of Melbourne, The National Vision Research Institute of Australia and Dept. of Optometry & Vision Sciences, 2007. / Typescript. Includes bibliographical references (leaves 95-111).

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<p>Based on evidence from studies involving animal single cell recording, animal brain lesion, and human brain damage, researchers have suggested that there may be differential visual representations for objects in near (peripersonal, within arm’s reach) and far (extrapersonal, beyond arm’s reach) space in the human visual system. The findings in Chapter 2 and Chapter 3 of the present thesis provide the first behavioural evidence suggesting that healthy human observers prefer to rely on different visual mechanisms in processing information in near and far spaces. The different performance in detecting visual targets presented in near and far space indicates that the brain can actively modulate the information processing either in parvocellular and magnocellular pathways or in ventral and dorsal streams. <br /> To determine the loci of the neural modulation regarding near and far viewing, visual identification tasks were employed in Chapter 4. In four experiments, visual stimuli were presented in either isoluminant green or achromatic white in order to decouple the neural processing in parvocellular and magnocellular pathways. The different patterns of the visual performance in the four experiments suggest that the change to near or far viewing distance results in altered information transmission in parvocellular and magnocellular pathways. Thus, the data in the present thesis provide the first behavioural evidence indicating that the LGN serves as a gatekeeper for regulating and redistributing visual information for later cortical analysis.</p> / Doctor of Science (PhD)

A distrofina é uma das proteínas que formam o complexo glicoproteico necessário para a integridade da fibra muscular e sua disfunção causa uma doença genética letal para os seres humanos, a distrofia muscular de Duchenne (DMD). Além do papel fundamental no tecido muscular, a distrofina é necessária para a fisiologia da retina e, portanto, para o processamento da informação visual. Estudos anteriores mostraram prejuízo assimétrico no eletrorretinograma (ERG), maior para aumento da luminância (via ON) que para diminuição (via OFF). Além disso, prejuízos na visão de cores e contrastes eram mais frequentes e severos em pacientes com alterações genéticas que comprometem a expressão da isoforma Dp260. O objetivo do presente estudo foi verificar através de protocolos eletrofisiológicos e psicofísicos se existiam diferenças nas respostas mediadas pelas vias visuais ON e OFF em jovens com DMD e como estas se relacionavam com o genótipo. Foram avaliados 19 jovens com DMD (idade média = 15,2 ± 3,4 anos) cujos resultados foram comparados com os de sujeitos controles pareados por idade. Os métodos utilizados foram o ERG de campo total e medidas psicofísicas de sensibilidade ao contraste (SC) espacial e temporal de luminância. Protocolos tradicionalmente empregados foram associados a protocolos cujos estímulos visuais ativam, preferencialmente, a via ON ou a via OFF. Para o ERG de campo total foram utilizados seis protocolos: 1. ERG escotópico, 2. ERG fotópico, 3 e 4. ERG mesópico ON e OFF, 5 e 6. ERG fotópico ON e OFF. Para os quatro últimos foram utilizados estímulos intermitentes com modulação da luminância em dente de serra, com aumento rápido de luminância e diminuição gradual (ON) e o contrário (OFF). Para a avaliação psicofísica foi determinada: 1. SC para grades senoidais e SC temporal, e 2. SC a estímulos de tabuleiro de xadrez com aumento (ON) ou diminuição (OFF) da luminância média relativa ao fundo, apresentados com duração curta (sistema magnocelular) ou longa (sistema parvocelular). Os resultados mostraram redução da amplitude da onda-b dos ERGs escotópico e fotópico e prejuízos na SC espacial e temporal de luminância, concordando com a literatura. A contribuição inédita do presente estudo foi mostrar alteração nos ERGs ON e OFF para atividade dos bastonetes e no ERG ON para atividade exclusiva dos cones. Na avaliação psicofísica, houve redução da SC para os protocolos ON sem diferença entre magnocelular e parvocelular. Em conclusão, as alterações encontradas estão principalmente relacionadas com a atividade ON da retina. A alteração psicofísica da SC espacial de luminância de jovens com DMD deve estar relacionada, ao menos em parte, com prejuízos retinianos devidos à ausência da Dp260 ou da própria distrofina total (Dp427). Estudos futuros devem aprofundar a investigação utilizando protocolos do ERG que estimulam, preferencialmente, as vias magnocelular e parvocelular, e ampliar o número de pacientes avaliados para se obter as correlações entre as alterações genéticas e os prejuízos visuais / The dystrophin is one of the proteins that form the glycoprotein complex necessary for the integrity of the muscular fibers. Its dysfunction causes a genetic disease called the Duchenne Muscular Dystrophy (DMD) which is lethal for humans. Besides its fundamental role in the muscle tissues the dystrophin is also necessary in the physiology of the retina, in the processing of visual information. Previous studies have demonstrated asymmetric deviations in the electroretinogram (ERG) of DMDs with bigger changes to stimuli with increasing (ON pathway) than to decreasing (OFF pathway) luminance. Moreover deficiencies in color vision and contrast sensitivity have been more frequent and severe in patients having genetic alterations related to the expression of the Dp260 isoform. The aim of the present study was to apply electrophysiological and psychophysical protocols to verify the suspected alterations in DMD patients regarding the ON and OFF visual pathways and relate the results to their genotypes. 19 DMD patients (mean age = 15.2 ± 3.4 years) were tested and their results were compared to that of an age-matched control group. Fullfield ERG and spatial and temporal luminance contrast sensitivity tests were used during the examinations. Classical protocols were applied together with the ones preferentially stimulating the ON and the OFF visual pathways. The full-field ERG test consisted of six protocols: 1. Scotopic ERG, 2. Photopic ERG, 3. and 4. Mesopic ON and OFF ERG, 5. and 6. Photopic ON and OFF ERG. For the latter four protocols flicker stimuli were used with sawtooth modulation of rapid increase and slower decrease in luminance (ON) and rapid decrease and slower increase in luminance (OFF). The psychophysical evaluation comprised 1. Spatial contrast sensitivity test with sinusoidal gratings and temporal contrast sensitivity test, and 2. Contrast sensitivity tests with checkerboard stimuli with increasing (ON) and decreasing (OFF) luminance relative to the background. These latter were presented for both short (magnocellular system) and long (parvocellular system) durations. In agreement with the literature the results show reduced amplitudes in the ERGs scotopic and photopic b-waves and also impairment in the spatial and temporal contrast sensitivities. This studys novel contribution was the presentation of the alterations in both rod driven ON and OFF ERGs and solely in the cone driven ON ERG. The psychophysical analysis showed reduced contrast sensitivity in the ON protocol similar for both magno- and parvocellular oriented stimuli. In summary the encountered alterations suggest damages in the ON mechanism of the retina. The changes in spatial luminance contrast sensitivity of DMD patients are related, at least partially, to the lack of Dp260 or to the loss of the entire dystrophin (Dp427). Future studies shall investigate this in more details applying ERG protocols to stimulate magno- and parvocellular activities, and increase the number of patients to be able to determine correlations between visual dysfunctions and genetic mutations

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abstract: The present study explores the role of motion in the perception of form from dynamic occlusion, employing color to help isolate the contributions of both visual pathways. Although the cells that respond to color cues in the environment usually feed into the ventral stream, humans can perceive motion based on chromatic cues. The current study was designed to use grey, green, and red stimuli to successively limit the amount of information available to the dorsal stream pathway, while providing roughly equal information to the ventral system. Twenty-one participants identified shapes that were presented in grey, green, and red and were defined by dynamic occlusion. The shapes were then presented again in a static condition where the maximum occlusions were presented as before, but without motion. Results showed an interaction between the motion and static conditions in that when the speed of presentation increased, performance in the motion conditions became significantly less accurate than in the static conditions. The grey and green motion conditions crossed static performance at the same point, whereas the red motion condition crossed at a much slower speed. These data are consistent with a model of neural processing in which the main visual systems share information. Moreover, they support the notion that presenting stimuli in specific colors may help isolate perceptual pathways for scientific investigation. Given the potential for chromatic cues to target specific visual systems in the performance of dynamic object recognition, exploring these perceptual parameters may help our understanding of human visual processing. / Dissertation/Thesis / M.A. Psychology 2011