Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 34-38). Also available via the Internet.

Objetivo: Avaliar a Função de Sensibilidade ao Contraste de Luminância Espacial e Temporal, estudar o desenvolvimento destas funções, a contribuição das vias de processamento paralelo para as funções de Sensibilidade ao Contraste e seu respectivo desenvolvimento e, por fim, determinar valores normativos destas funções visando uma aplicabilidade clínica.Método A avaliação psicofísica de sensibilidade ao contraste de luminância espacial e temporal foi realizada em 112 sujeitos divididos em três grupos:GrupoI ( idade média =9,14±2,7 anos),Grupo II ( idade média=23,7 ± 3,4 anos) e Grupo III ( idade média=41,8± 5,5 anos) com o programa PSYCHO for Windows Versão 2.36 (Cambridge Research Systems, CRS-Ltd, UK) acoplado a um microcomputador PC XTC -600. . Os estímulos foram apresentados em um monitor Sony Triniton de 19 polegadas GFD420 (Sony Corporation, USA) com resolução espacial de 800X600 e resolução temporal de 69 Hz Os estímulos eram comandados pela placa gráfica VSG 2/4 (Cambridge Research Systems, CRS-Ltd, UK).Resultados A avaliação psicofísica para a sensibilidade ao contraste espacial e temporal mostraram que esta função já está desenvolvida e em pleno funcionamento em crianças (6 anos) ocorrendo um declínio para as frequências espaciais de 2,0cpg;8,3cpg e 14,5cpg para os grupos II e III.Para a frequência temporal de 2,5Hz o declínio ocorre nos Grupos II e III e para a frequência temporal de 5,0 Hz nas idades mais avançadas(GIII). Para o estudo da contribuição das vias de processamento paralelo (magnocelular e parvocelular) podemos notar uma maior sensibilidade ao contraste para decremento de luz do que para incremento de luz, porém não foi possível determinar a real contribuição dessas vias para a função de sensibilidade ao contraste. Conclusão Avaliamos com sucesso a Sensibilidade ao Contraste Espacial e Temporal para todas as faixas etárias e, assim, conseguimos ter acesso ao desenvolvimento desta função, entre as idades de 6 e 57 anos. Valores normativos para as tais funções foram estabelecidos por metodologia nãoparamétrica.. O estudo da contribuição das vias magnocelular e parvocelular não pode ser conclusivo, porém os achados mostraram uma maior sensibilidade para o decremente de luz o que corrobora com a literatura / Purpose: To analyze the spatial and temporal luminance contrast sensitivity function, to study the development of these functions, the contribution of the parallel processing pathways and to determine the normative values of these functions to order a clinical applicability normative. Methods the psychophysical evaluation of the spatial and temporal luminance contrast sensitivity was performed in 112 subjects divided into three groups: Group I (mean age =9.14±2.7 years), Group II (mean age=23.7 ± 3.4 years) and Group III (mean age=41.8± 5.5 years) with the PSYCHO for Windows Version 2.36 (Cambridge Research Systems, CRS-Ltd, UK) connect to the microcomputer PC XTC -600. The stimuli was showed in a monitor Sony Triniton de 19 inches GFD420 (Sony Corporation, USA) with spatial resolution of the 800X600 and temporal resolution of the 69 Hz. The stimuli was made by the graphics card VSG 2/4 (Cambridge Research Systems, CRS-Ltd, UK).Results The psychophysics evaluation to spatial and temporal contrast sensitivity showed that this function is already developed and full operation in children (6 years old) with a decline to spatial frequencies of 2.0cpg;8.3cpg and 14.5 cpg to the groups II and III. For the temporal frequency of 2.5Hz the decline occur to the groups II and III .and to the temporal frequency of 5.0 Hz the decline occur to the advantage ages(GIII). For the study of the parallel processing pathways (magnocellular e parvocellular) we can see bigger contrast sensitivity to decrement than to increment of light. It was not possible determine the real contribution of these pathways to the contrast sensitivity function. Conclusion We evaluated in a successful way the spatial and temporal contrast sensitivity to all age range and so we could access the development of this function between the ages from 6 to 57 years old. Normatives values to this function were established for non parametric methodology. The study of the contribution of the parvocellular and magnocellular pathways is not conclusive, but the results showed a bigger sensibility to decrement than to increment of light that was similar to the literature

Objetivo: Avaliar a Função de Sensibilidade ao Contraste de Luminância Espacial e Temporal, estudar o desenvolvimento destas funções, a contribuição das vias de processamento paralelo para as funções de Sensibilidade ao Contraste e seu respectivo desenvolvimento e, por fim, determinar valores normativos destas funções visando uma aplicabilidade clínica.Método A avaliação psicofísica de sensibilidade ao contraste de luminância espacial e temporal foi realizada em 112 sujeitos divididos em três grupos:GrupoI ( idade média =9,14±2,7 anos),Grupo II ( idade média=23,7 ± 3,4 anos) e Grupo III ( idade média=41,8± 5,5 anos) com o programa PSYCHO for Windows Versão 2.36 (Cambridge Research Systems, CRS-Ltd, UK) acoplado a um microcomputador PC XTC -600. . Os estímulos foram apresentados em um monitor Sony Triniton de 19 polegadas GFD420 (Sony Corporation, USA) com resolução espacial de 800X600 e resolução temporal de 69 Hz Os estímulos eram comandados pela placa gráfica VSG 2/4 (Cambridge Research Systems, CRS-Ltd, UK).Resultados A avaliação psicofísica para a sensibilidade ao contraste espacial e temporal mostraram que esta função já está desenvolvida e em pleno funcionamento em crianças (6 anos) ocorrendo um declínio para as frequências espaciais de 2,0cpg;8,3cpg e 14,5cpg para os grupos II e III.Para a frequência temporal de 2,5Hz o declínio ocorre nos Grupos II e III e para a frequência temporal de 5,0 Hz nas idades mais avançadas(GIII). Para o estudo da contribuição das vias de processamento paralelo (magnocelular e parvocelular) podemos notar uma maior sensibilidade ao contraste para decremento de luz do que para incremento de luz, porém não foi possível determinar a real contribuição dessas vias para a função de sensibilidade ao contraste. Conclusão Avaliamos com sucesso a Sensibilidade ao Contraste Espacial e Temporal para todas as faixas etárias e, assim, conseguimos ter acesso ao desenvolvimento desta função, entre as idades de 6 e 57 anos. Valores normativos para as tais funções foram estabelecidos por metodologia nãoparamétrica.. O estudo da contribuição das vias magnocelular e parvocelular não pode ser conclusivo, porém os achados mostraram uma maior sensibilidade para o decremente de luz o que corrobora com a literatura / Purpose: To analyze the spatial and temporal luminance contrast sensitivity function, to study the development of these functions, the contribution of the parallel processing pathways and to determine the normative values of these functions to order a clinical applicability normative. Methods the psychophysical evaluation of the spatial and temporal luminance contrast sensitivity was performed in 112 subjects divided into three groups: Group I (mean age =9.14±2.7 years), Group II (mean age=23.7 ± 3.4 years) and Group III (mean age=41.8± 5.5 years) with the PSYCHO for Windows Version 2.36 (Cambridge Research Systems, CRS-Ltd, UK) connect to the microcomputer PC XTC -600. The stimuli was showed in a monitor Sony Triniton de 19 inches GFD420 (Sony Corporation, USA) with spatial resolution of the 800X600 and temporal resolution of the 69 Hz. The stimuli was made by the graphics card VSG 2/4 (Cambridge Research Systems, CRS-Ltd, UK).Results The psychophysics evaluation to spatial and temporal contrast sensitivity showed that this function is already developed and full operation in children (6 years old) with a decline to spatial frequencies of 2.0cpg;8.3cpg and 14.5 cpg to the groups II and III. For the temporal frequency of 2.5Hz the decline occur to the groups II and III .and to the temporal frequency of 5.0 Hz the decline occur to the advantage ages(GIII). For the study of the parallel processing pathways (magnocellular e parvocellular) we can see bigger contrast sensitivity to decrement than to increment of light. It was not possible determine the real contribution of these pathways to the contrast sensitivity function. Conclusion We evaluated in a successful way the spatial and temporal contrast sensitivity to all age range and so we could access the development of this function between the ages from 6 to 57 years old. Normatives values to this function were established for non parametric methodology. The study of the contribution of the parvocellular and magnocellular pathways is not conclusive, but the results showed a bigger sensibility to decrement than to increment of light that was similar to the literature

The purpose of this study was to examine the use of colored overlays as an aid to individuals with reading problems; and, in particular, to assess the role visual contrast sensitivity may play in this treatment and in reading problems in general. Arguments both supporting and refuting the validity of the Irlen technique of using colored overlays and lenses as a treatment for reading problems are reviewed. While much of the criticism regarding the Irlen technique appears warranted, it seems that, for many reading disabled individuals, overlays and lenses do provide relief from symptoms and help to raise scores on reading tests. Tinted overlays may work by improving the contrast ratio of print for those with poorer contrast sensitivity. It was hypothesized that reading scores of many poor readers would improve with the addition of tinted overlays, that those who were helped would show poorer contrast sensitivity than those who were not, that contrast sensitivity would also improve with the addition of a tinted overlay, and that subjects would be equally helped bv a neutral density gray overlay. One-hundred-seventy-four undergraduate volunteers were screened for reading ability with the Nelson Denny Reading Comprehension Test. The top 46 and bottom 46 were divided into three groups who were tested again using either a) one of four overlays deemed "optimal" for that subject by performance on the Tinker Speed of Reading test b) a gray overlay of the same density or c) no overlay. Contrast sensitivity was also tested under both conditions. The Irlen effect was not seen with this group of subjects. Results showed no significant effect of group or overlay color on reading performance. Scores in general increased significantly on the second trial, with low readers improving more than high readers. Contrast sensitivity showed no relationship to reading indices. / Master of Science

Yes / Purpose.: To establish whether a clinically exploitable relationship exists between surrogate measures of retinal ganglion cell number and functional sampling density and visual contrast sensitivity in healthy young eyes. Methods.: Psychometric functions for contrast detection were measured at 9° eccentricity in superior and inferior visual field from 20 healthy adults (age 23–43, median 26 years). Functions were compared with corresponding localized regions of retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography, a surrogate of retinal ganglion cell number, and to grating resolution acuity, a psychophysical surrogate of retinal ganglion cell sampling density. Correlations between psychometric function parameters and retinal ganglion cell surrogates were measured by Spearman's rank correlation. Results.: All measures exhibited a 2- to 4-fold variation in our sample. Despite this, correlations between measures were weak. Correlations between psychometric function parameters (threshold, spread) and RNFL thickness ranged in magnitude from 0.05 to 0.19 (P = 0.43–0.85). Grating resolution was sampling limited for 16 of 20 participants in superior visual field, and for 12 of 20 participants in inferior visual field. Correlations between psychometric function parameters and grating resolution acuities ranged in magnitude from 0.05 to 0.36 (P = 0.12–0.85) when all data were considered, and from 0.06 to 0.36 (P = 0.26–0.87) when only sampling-limited data were considered. Conclusions.: Despite considerable variation in both psychometric functions for contrast detection and surrogate measures of retinal ganglion cell number and sampling density among healthy eyes, relationships between these measures are weak. These relationships are unlikely to be exploitable for improving clinical tests in healthy populations.

Indiana University-Purdue University Indianapolis (IUPUI) / Alzheimer’s disease (AD) is the most common age-related neurodegenerative disease. Many researchers believe that an effective AD treatment will prevent the development of disease rather than treat the disease after a diagnosis. Therefore, the development of tools to detect AD-related pathology in early stages is an important goal. In this report, MRI-based markers of neurodegeneration are explored as biomarkers of AD. In the first chapter, the sensitivity of cross-sectional MRI biomarkers to neurodegenerative changes is evaluated in AD patients and in patients with a diagnosis of mild cognitive impairment (MCI), a prodromal stage of AD. The results in Chapter 1 suggest that cross-sectional MRI biomarkers effectively measure neurodegeneration in AD and MCI patients and are sensitive to atrophic changes in patients who convert from MCI to AD up to 1 year before clinical conversion. Chapter 2 investigates longitudinal MRI-based measures of neurodegeneration as biomarkers of AD. In Chapter 2a, measures of brain atrophy rate in a cohort of AD and MCI patients are evaluated; whereas in Chapter 2b, these measures are assessed in a pre-MCI stage, namely older adults with cognitive complaints (CC) but no significant deficits. The results from Chapter 2 suggest that dynamic MRI-based measures of neurodegeneration are sensitive biomarkers for measuring progressive atrophy associated with the development of AD. In the final chapter, a novel biomarker for AD, visual contrast sensitivity, was evaluated. The results demonstrated contrast sensitivity impairments in AD and MCI patients, as well as slightly in CC participants. Impaired contrast sensitivity was also shown to be significantly associated with known markers of AD, including cognitive impairments and temporal lobe atrophy on MRI-based measures. The results of Chapter 3 support contrast sensitivity as a potential novel biomarker for AD and suggest that future studies are warranted. Overall, the results of this report support MRI-based measures of neurodegeneration as effective biomarkers for AD, even in early clinical and preclinical disease stages. Future therapeutic trials may consider utilizing these measures to evaluate potential treatment efficacy and mechanism of action, as well as for sample enrichment with patients most likely to rapidly progress towards AD.