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Ghim, Mimi M. "Spatial contrast sensitivity of birds." College Park, Md. : University of Maryland, 2003. http://hdl.handle.net/1903/65.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2003.Thesis research directed by: Psychology. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Olesko, Brian M. "Dynamic contrast sensitivity : methods and measurements /." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09052009-040416/.
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Barten, Peter G. J. "Contrast sensitivity of the human eye and its effects on image quality." Bellingham, Wash. (1000 20th St. Bellingham WA 98225-6705 USA) : SPIE, 1999. http://dx.doi.org/10.1117/3.353254.
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Thesis (doctoral)--Technische Universiteit Eindhoven, 1999."SPIE digital library." Originally published: Knegsel : HV Press, 1999. Includes bibliographical references and index. Also available in print version.
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Ukkonen, Outi I. "Contrast sensitivity for complex and random gratings." Thesis, Aston University, 1995. http://publications.aston.ac.uk/14610/.
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This thesis studied the effect of (i) the number of grating components and (ii) parameter randomisation on root-mean-square (r.m.s.) contrast sensitivity and spatial integration. The effectiveness of spatial integration without external spatial noise depended on the number of equally spaced orientation components in the sum of gratings. The critical area marking the saturation of spatial integration was found to decrease when the number of components increased from 1 to 5-6 but increased again at 8-16 components. The critical area behaved similarly as a function of the number of grating components when stimuli consisted of 3, 6 or 16 components with different orientations and/or phases embedded in spatial noise. Spatial integration seemed to depend on the global Fourier structure of the stimulus. Spatial integration was similar for sums of two vertical cosine or sine gratings with various Michelson contrasts in noise. The critical area for a grating sum was found to be a sum of logarithmic critical areas for the component gratings weighted by their relative Michelson contrasts. The human visual system was modelled as a simple image processor where the visual stimuli is first low-pass filtered by the optical modulation transfer function of the human eye and secondly high-pass filtered, up to the spatial cut-off frequency determined by the lowest neural sampling density, by the neural modulation transfer function of the visual pathways. The internal noise is then added before signal interpretation occurs in the brain. The detection is mediated by a local spatially windowed matched filter. The model was extended to include complex stimuli and its applicability to the data was found to be successful. The shape of spatial integration function was similar for non-randomised and randomised simple and complex gratings. However, orientation and/or phase randomised reduced r.m.s contrast sensitivity by a factor of 2.
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Drover, James R. "Modification of the infant contrast sensitivity card procedure." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ55503.pdf.
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Yap, M. K. H. "Clinical application of contrast sensitivity in visual dysfunction." Thesis, University of Bradford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371489.
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Tunnacliffe, A. H. "Contrast sensitivity as an indicator of binocular function." Thesis, University of Bradford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376693.
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Osman, Mawada. "Contrast Sensitivity and Visual Acuity among the Elderly." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586874623985066.
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Mason, Alexandra J. S. "The contrast sensitivity of three groups of opthalmological patients." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336141.
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Grey, C. P. "Changes in contrast sensitivity during soft contact lens wear." Thesis, University of Bradford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376712.
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Ong, Gek-Lim. "Instrumentation for automated contrast-sensitivity and colour-vision tests." Thesis, University of Sussex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270712.
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Persaud, Steven S. "Contrast Sensitivity to One- and Two-Dimensional Luminance Patterns." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/9910.
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Contrast sensitivities to one- and two-dimensional luminance patterns were compared in a two-alternative forced choice (2AFC) experiment. Space-averaged luminance was also manipulated. Statistical analyses revealed a main effect of stimulus dimension (p < .05) and no effect of space-averaged luminance. The main effect of stimulus dimension was explained in terms of an on-center, off-center receptive field model combined with watershed spatial vision behavior at spatial frequencies below 1 cycle-per-degree (cpd). The non-significant result for space-averaged luminance was explained by the limited range of manipulation of the variable. Two-dimensional luminance patterns were suggested as ideal patterns for reconciling grating-based spatial vision research with spatial vision behavior in an ecological context. Future research directions are suggested.Master of Science
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Young, Anthony M. "Investigation of Laser Speckle Contrast Imaging's Sensitivity to Flow." Miami University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=miami153256524246362.
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Njeru, Steve Murimi Mathenge. "Contrast Sensitivity and Visual Acuity in Low-Vision Students." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586966057072378.
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Croxton, Craig A. "The effects of target orientation on the dynamic contrast sensitivity function." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-09052009-040820/.
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Adams, William F. "The effects of target vibration on the human contrast sensitivity function." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-11102009-020033/.
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Govan, Donovan G., and n/a. "Luminance and contrast as depth cues." University of Otago. Department of Psychology, 2007. http://adt.otago.ac.nz./public/adt-NZDU20080129.112322.
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It has long been held that luminance acts as a cue for depth perception. But varying the luminance of a stimulus inevitably alters its contrast with its background. Recent research shows that contrast is a depth cue. I have distinguished two kinds of contrast, external contrast, the contrast of a stimulus with its background, and internal contrast, the contrast within the stimulus. I compared the relative apparent depth of two stimuli (both directly and indirectly; stimuli were either sine-wave filled hemifields, sine-wave filled squares, or plain squares), as their luminances and internal contrasts were varied along with the luminance of their background. I found internal and external contrast to be additive effects, whereby the stimulus with either a higher internal or external contrast appeared nearer. When the internal and external contrasts of the stimuli were equated, luminance acted as an ambiguous cue, with the lighter square appearing nearer for the majority of observers, and farther for a minority. Luminance may act as a depth cues from our experience with artificial lighting (artificial light varies ambiguously with depth). Contrast may act as a depth cue from its usual association with the reduction of contrast of objects with distance through the atmosphere. I conclude that luminance and contrast are independent depth-cues that are caused by two different mechanisms.
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Dahl, Howard Stewart. "Comparison of spatial contrast sensitivity between younger and older observers." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25373.
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Contrast sensitivity to vertically oriented grating patterns with a sinusoidal luminance profile were examined between groups of observers varying either in gender or age. For each observer at each of the seven spatial frequencies tested (.75, 1.5, 3, 6, 7.5, 10, 15 cyc/deg) threshold values were calculated for either ascending or descending trials as well as a combination of both. These threshold values were numerically transformed into sensitivity values and contributed to a group mean contrast sensitivity score for each spatial frequency. No significant effect of gender was found but younger observers (mean age=22.6 yrs.) exhibited significantly better contrast sensitivity than the older aged group (mean age=66.2 yrs.) for ascending trials at 3, 1.5 and .75 cyc/deg--the lowest spatial frequencies tested. Contrast sensitivity was also correlated with various measures.
These findings were discussed in relation to the existing literature on age and spatial contrast sensitivity and since the machine used to examine the contrast sensitivity function (CSF) in this study utilized a laser interferometric method of stimulus generation, possible neurological changes with aging to explain this noted loss were also considered. Also discussed were various parameters that effect the CSF with a view toward explaining the disparate findings of various existing studies of age and the CSF.Arts, Faculty of
Psychology, Department of
Graduate
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Lynk, Lisa. "Aging effects of binocular summation on contrast sensitivity and hyperacuity." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0009/MQ34976.pdf.
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Hood, Alison S. "The dependence of binocular contrast sensitivity on binocular single vision." Thesis, University of Glasgow, 1999. http://theses.gla.ac.uk/6253/.
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This study involved the determination of the effects of binocular viewing on contrast sensitivities in 11 normal subjects and in different categories of amblyopes. These were simple anisometropic amblyopes (n=9), micro-esotropic amblyopes with anomalous BSV (n=6), esotropic amblyopes with anomalous BSV (n=3) esotropic without BSV 9n=5), exotropic amblyopes without BSV (n=2) and a group of non-amblyopic strabismics (non-amblyopic esotropes without BSV (n=4); non-amblyopic exotropes without BSV (n=2).An ophthalmic examination was carried out on all individuals. The examination procedures undertaken comprised determination of the visual acuity, subjective refraction, the results of which were confirmed by retinoscopy, and assessment of uniocular fixation patterns. The state of BSV, the direction and magnitude of the angle of deviation, the amplitude of accommodation and pupillary diameter were also determined. The subjects were accordingly placed into the appropriate groups on the basis of the basis of the results of the ophthalmic examination. Measurement of uniocular and binocular contrast sensitivities in response to stationary vertical sinusoidal grating patterns were undertaken. The stimulus display consisted of a Tektronix 5103 cathode ray tube (CRT) with a screen subtense of 2 degrees. Mean contrast threshold values were measured for monocular and binocular viewing over the range of spatial frequencies studied which varied between 8c/deg to 40c/deg depending on the group being examined. The conclusions reached were, first, in individuals with BSV (normal or anomalous), binocular enhancement of contrast sensitivities occurred. However, strabismic amblyopes without BSV and non-amblyopic strabismics without BSV did not exhibit enhanced binocular contrast sensitivities; on the contrary, binocular contrast sensitivities were reduced compared to those obtained through the better eye. Furthermore, when bifoveal stimulation was effected, a further reduction in binocular contrast sensitivity occurred. This study has thus shown that binocular contrast sensitivities are augmented compared with monocular contrast sensitivities when BSV is present, but are decreased when BSV is absent. Furthermore, correction of the angle of squint in strabismics, whether BSV is present or not, further reduces the binocular contrast sensitivities.
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Zavod, Merrill. "THE EFFECTS OF STIMULUS MOTION ON CONTRAST SENSITIVITY: DYNAMIC SENSI." Doctoral diss., University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3724.
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Static Visual Acuity (SVA) has been called into question for some time as a measure of overall visual system function and as a predictor of performance on real-life tasks requiring vision (i.e., operating an automobile). Specifically, it has been pointed out that the targets employed in most SVA testing (high contrast, stationary letters) are an insufficient analog to actual targets encountered in everyday activities, which are often in motion and/or of less-than-perfect contrast. In addition, the size-threshold methodology typically used to measure SVA is incongruent with current theories of a multi-channel visual system. Dynamic Visual Acuity (DVA) and Contrast Sensitivity have been suggested as alternatives to SVA, but while each mitigates specific weaknesses of the SVA measure, neither addresses the shortcomings completely. Traditional DVA measures employ moving targets, but these targets are usually of perfect contrast and a size-threshold methodology is used to specify acuity levels. Contrast Sensitivity employs a contrast-threshold methodology and allows measurement of specific visual channels, but stationary targets are utilized. The present study combined the DVA and Contrast Sensitivity measures in an effort to retain the unique qualities of each while addressing their shortcomings, resulting in a more detailed picture of the human visual system and functioning than has yet been possible. By measuring contrast sensitivity to targets at a set of spatial frequencies spanning the human "window of visibility" and under conditions of motion representative of that encountered in everyday activities, it was hoped that a more powerful predictor of actual visual performance would be created. In addition, normative data was established for two separate age populations, in the hopes of learning more about specific changes that occur to the visual system during the aging process. Indeed, several effects and interactions among the three main variables (spatial frequency, velocity, age) were uncovered, which appears to indicate that the new test may provide more information about the visual system than DVA or contrast sensitivity by themselves. The ramifications of this effort to human factors and visual performance research are discussed along with recommendations for the continuation and application of this line of research.Ph.D.
Department of Psychology
Arts and Sciences
Psychology
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Tumblin, John Erwin (Jack). "Three methods of detail-preserving contrast reduction for displayed images." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/13080.
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Sharma, Saloni. "The effect of L-dopa on contrast sensitivity in normal subjects using functional magnetic resonance imaging." Morgantown, W. Va. : [West Virginia University Libraries], 2003. http://etd.wvu.edu/templates/showETD.cfm?recnum=2973.
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Thesis (M.S.)--West Virginia University, 2003.Title from document title page. Document formatted into pages; contains xi, 101 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 95-99).
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Griffiths, Stella N. "The effect of intraocular scattered light on the contrast sensitivity function." Thesis, Aston University, 1986. http://publications.aston.ac.uk/14587/.
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Intraocular light scatter is high in certain subject groups eg the elderly, due to increased optical media turbidity, which scatters and attenuates light travelling towards the retina. This causes reduced retinal contrast especially in the presence of glare light. Such subjects have depressed Contrast Sensitivity Functions (CSF). Currently available clinical tests do not effectively reflect this visual disability. Intraocular light scatter may be quantified by measuring the CSF with and without glare light and calculating Light Scatter Factors (LSF). To record the CSF on clinically available equipment (Nicolet CS2000), several psychophysical measurement techniques were investigated, and the 60 sec Method of Increasing Contrast was selected as the most appropriate. It was hypothesised that intraocular light scatter due to particles of different dimensions could be identified by glare sources at wide (30°) and narrow (3.5°) angles. CSFs andLSFs were determined for: (i) Subjects in young, intermediate and old age groups. (ii) Subjects during recovery from large amounts of induced corneal oedema. (iii) A clinical sample of contact lens (CL) wearers with a group of matched controls. The CSF was attenuated at all measured spatial frequencies with the intermediate and old group compared to the young group. High LSF values were found only in the old group (over 60 years). It was concluded that CSF attenuation in the intermediate group was due to reduced pupil size, media absorption and/or neural factors. In the old group, the additional factor was high intraocular light scatter levels of lenticular origin. The rate of reduction of the LSF for the 3.5° glare angle was steeper than that for the 30° angle, following induced corneal oedema. This supported the hypothesis, as it was anticipated that epithelial oedema would recover more rapidly than stromal oedema. CSFs and LSFs were markedly abnormal in the CL wearers. The analytical details and the value of these investigative techniques in contact lens research are discussed.
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Martins, Cristiane Maria Gomes. "Impacto da catarata congênita na sensibilidade ao contraste espacial de luminância em crianças." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/47/47135/tde-15032013-105656/.
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A opacificação do cristalino presente ao nascimento ou nos primeiros meses de vida é denominada de Catarata Congênita (CC). As primeiras semanas de vida são importantes no desenvolvimento visual, já que há diferença significativa no desempenho visual de crianças que passaram pela cirurgia até seis semanas de vida (com melhor desempenho visual) em relação às crianças que realizaram a cirurgia após seis semanas de vida. Crianças que tiveram privação visual durante a primeira infância por catarata bilateral apresentam redução da visão espacial. O objetivo deste trabalho foi verificar o impacto na Função de Sensibilidade ao Contraste (FSC) em crianças de tratamento cirúrgico de Catarata Congênita, durante a fase de desenvolvimento visual. Foram avaliados três grupos: 11 crianças do grupo controle (média idade =6,83; DP=1,38), 9 crianças do grupo CC (média idade =6,87; DP=2,03) e 15 indivíduos adultos (média idade =27,63; DP=4,16). Foi utilizado o software Metropsis para avaliação da sensibilidade ao contraste de luminância de grade senoidal nas frequências espaciais de 0,2 cpg; 0,5 cpg; 1,0 cpg; 2,0 cpg; 4,2 cpg e 8,9 cpg e luminância média de 34,4 cd/m². Houve redução em toda a curva de sensibilidade ao contraste (SC) do grupo CC quando comparado ao grupo controle e não houve relação entre o tempo de privação e a redução da SCThe opacification of the lens present at birth is called Congenital Cataract (CC). The first weeks of life are important in visual development since there is not any significant difference in visual performance of children who had surgery within six weeks of life (with better visual performance) compared with children who underwent surgery after this period. Children who have visual deprivation during infancy due to bilateral cataracts have reduced spatial vision. The aim of this study was to assess the impact on Contrast Sensitivity Function (CSF) in children with Congenital Cataract surgery during the visual development age range. We evaluated three groups: 11 control children (mean age = 6.83, SD = 1.38), 9 children in the CC group (mean age = 6.87, SD = 2.03) and 15 adults (mean age = 27.63, SD = 4.16). Metropsis software was used to evaluate sensitivity to luminance contrast of the sinusoidal grating spatial frequencies of 0.2 cpd, 0.5 cpd, 1.0 cpd, 2.0 cpd, 4.2 cpd and 8.9 cpd with an average luminance of 34.4 cd / m². There was a reduction in the contrast sensitivity function (CSF) of the CC group compared to the control group and there was no correlation between the duration of deprivation and the impairment in the SC
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Masson, Andrªe P. "The effect of aging and visual impairments on spatio-temporal contrast sensitivity." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25919.pdf.
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Perron, Adena Marie. "The effect of vigabatrin treatment on contrast sensitivity in a pediatric population." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ63152.pdf.
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Diamond, Mark R. "The effect of saccades on visual sensitivity and time perception /." Connect to this title, 2002. http://theses.library.uwa.edu.au/adt-WU2003.0038.
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Midgley, Caroline Ann. "Binocular interactions in human vision." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4839/.
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Early visual processing is subject to binocular interactions because cells in striate cortex show binocular responses and ocular dominance (Hubel & Weisel, 1968). The work presented in this thesis suggests that these physiological interactions can be revealed in psychophysical experiments using normal human observers. In the region corresponding to the blind spot, where binocular interactions differ from areas of the visual field which are represented by two eyes, monocular contrast sensitivity is increased. This finding can be partially explained by an absence of normal binocular interactions in this location (Chapter 2). A hemianopic patient was studied in an attempt to discover whether the effect in normal observers was mediated by either a mechanism in striate cortex or via a subcortical pathway. However, the results were unable to distinguish between these two explanations (Chapter 3).In a visual search task, no difference in reaction time was observed for targets presented to the region corresponding to the blind spot compared with targets presented to adjacent binocularly represented areas of the visual field. Since performance was unaffected by the monocularity of the region corresponding to the blind, pop-out for orientation may be mediated beyond striate cortex where cells are binocularly balanced (Chapter 5). Further support for this contention was provided by studies of orientation pop-out in central vision which found that dichoptic presentation of stimuli did not affect the degree of pop-out obtained and that in general, visual search for a target based solely on eye of origin is impossible (Chapter 6). However, a task that measured orientation difference sensitivity more directly than the search experiments, found that thresholds were higher for dichoptically presented stimuli. This suggests the involvement of neurons that receive a weighted input from each eye. A model of orientation difference coding can account for the results by assuming that the range of inhibition across which orientation differences are coded is narrower for dichoptic stimuli leading to a greater resolvable orientation difference (Chapter 7).
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Ledeatte, Barry Anderson. "Spatial summation in the human visual system." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243775.
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Thomas, Kathleen Theresa. "Do colored overlays improve reading? : a test of the Irlen effect /." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06162009-063332/.
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Moreira, Sonia Maria Cipriani Fersura. "Desenvolvimento da sensibilidade ao contraste de luminância espacial e temporal." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/47/47132/tde-21102010-110538/.
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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 literaturaPurpose: 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
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Khalil, Nofal Mohammed. "Investigations of visual function in migraine by visual evoked potentials and visual psychophysical tests." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/8336.
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Wagge, Jordan Rose. "Contributions of response gain and contrast gain to human spatial pattern masking." Oxford, Ohio : Miami University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1250003782.
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Mekaroonreung, Haruetai. "Trait-Based Individual Differences on Discomfort Glare Rating Responses and Related Visual Contrast Sensitivity." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/43879.
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This research was designed to investigate the relationship between Trait-based Individual differences (neuroticism and extraversion) and glare subjective responses as well as the actual contrast sensitivity when exposed to the same manipulated glare condition. In addition, the relationship between the glare subjective responses and actual contrast sensitivity was investigated. To examine the trait-based individual differences, the International Personality Item Pool (IPIP) was used while the subjective glare experience was examined utilizing modified glare discomfort rating scale. The visual performance was measured through the contrast sensitivity level using adjustable contrast level of the Landolt's C target. This investigation compared 36 individuals (9 high neuroticism scorers, 9 low neuroticism scorers, 9 high extraversion scorers, and 9 low extraversion scorers) on subjective discomfort glare rating responses and visual contrast sensitivity. The study is directed toward improving our understanding of influencing factors on the experience of discomfort glare, which may eventually be applied to the design of glare measurement methods, and toward training and selection of drivers and workers who may work under conditions of glare. Results indicated significant effect of extraversion trait on rating response while insignificant effect on visual related performance was found. The relationships between rating response and visual performance were also found to be quite low in this study. In conclusion, the expected model was supported but only on the extraversion trait.Master of Science
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Mustonen, Juvi K. "Spatial contrast sensitivity and external noise: applications to optical and neural modulation transfer functions." Thesis, Aston University, 1995. http://publications.aston.ac.uk/14551/.
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The thesis will show how to equalise the effect of quantal noise across spatial frequencies by keeping the retinal flux (If-2) constant. In addition, quantal noise is used to study the effect of grating area and spatial frequency on contrast sensitivity resulting in the extension of the new contrast detection model describing the human contrast detection system as a simple image processor. According to the model the human contrast detection system comprises low-pass filtering due to ocular optics, addition of light dependent noise at the event of quantal absorption, high-pass filtering due to the neural visual pathways, addition of internal neural noise, after which detection takes place by a local matched filter, whose sampling efficiency decreases as grating area is increased. Furthermore, this work will demonstrate how to extract both the optical and neural modulation transfer functions of the human eye. The neural transfer function is found to be proportional to spatial frequency up to the local cut-off frequency at eccentricities of 0 - 37 deg across the visual field. The optical transfer function of the human eye is proposed to be more affected by the Stiles-Crawford -effect than generally assumed in the literature. Similarly, this work questions the prevailing ideas about the factors limiting peripheral vision by showing that peripheral optical acts as a low-pass filter in normal viewing conditions, and therefore the effect of peripheral optics is worse than generally assumed.
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Longley, Christopher I. "Contrast sensitivity and glare : new measurement techniques and the visual consequences of wearing head-mounted displays." Thesis, University of Bradford, 2016. http://hdl.handle.net/10454/16061.
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The main aim of this thesis was to evaluate the performance of the contrast sensitivity clock (CSC), a new screening device for measuring contrast sensitivity (CS) and glare. This device allows CS without glare, with glare and disability glare scores to be recorded. After initial data collection the design of the CSC was slightly amended improving the performance of the device. The amended design of the CSC was shown to be a valid, discriminative and repeatable measure for purpose. The CSC is also a quick test to perform and is relatively cheap to produce. If all these factors are considered it shows potential to become the test of choice for the assessment of visual glare. A head-mounted display system was also evaluated in terms of the glare effects it may cause. The monocular display screen of the device significantly reduced the CS of the eye directly exposed but also had an effect on binocular performance, reducing amounts of binocular summation. Electronic devices, including head-mounted displays and satellite navigation systems can seriously affect CS at low luminance levels, similar to those found when driving at night.
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Haller, Nicola Kristin [Verfasser]. "The influence of motion on spatial contrast sensitivity in budgerigars (Melopsittacus undulatus) / Nicola Kristin Haller." Hannover : Bibliothek der Tierärztlichen Hochschule Hannover, 2014. http://d-nb.info/1064863604/34.
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Hopkins, Gregory Robert II. "Contrast sensitivity and vision-related quality of life assessment in the pediatric low vision population." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397751785.
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Kim, Kerry Justin. "Sites and mechanisms of temporal contrast adaptation in the salamander retina /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/10542.
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Bontrager, Jordan G. "Characterization and Applications for A Polymerized DiaCEST Contrast Agent." Thesis, The University of Arizona, 2015. http://hdl.handle.net/10150/577329.
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MRI can benefit from an increase in the sensitivity of contrast agents. The CEST MRI technique in particular suffers from very poor sensitivity when using diamagnetic contrast agents. Polymerized CEST MRI contrast agents could increase the sensitivity per macromolecule over monomer contrast agents. The increase in sensitivity is related to the increase in number of contrast agents per polymer. A contrast agent with increased sensitivity can be used to image on the molecular level in vivo, where the concentration of targets is very low. A polymerized diaCEST contrast agent was synthesized by coupling a salicylic acid analogue to a poly (acrylic acid) backbone. The CEST effect of the coupled analogue was compared to its uncoupled form for different concentrations and pH values. A RL-QUEST method was used to calculate the exchange rate of the analogue for different pH values before and after coupling. The polymerized diaCEST agent was attempted to be loaded into DOPC and bis-SorbPC liposomes, and was also attempted to be targeted to folate receptors in a KB cell culture. These studies establish the foundation for translation of polymerized diaCEST contrast agents to additional in vitro and in vivo investigations.
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Henderson, Albert Steven. "Contrast sensitivity for drifting sine wave gratings in near visual periphery predicts older drivers' accident risk." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104505.
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Drivers over the age of 70 have a significantly higher rate of intersection collisions than younger drivers. Many of their accidents involve a visual detection error, resulting in a right-of-way violation and a collision with an oncoming vehicle. Three studies relating older drivers' peripheral motion detection to accident risk demonstrate that peripheral motion contrast threshold (PMCT) for low spatial frequency drifting sine wave gratings significantly declines with age, and that PMCT predicts about 40% of driving performance variance (p > .001). Approximately twenty older drivers participated in each study. In all three studies, older drivers' PMCT was assessed using forced choice psychophysical procedures, with 0.4 cycle/degree sine wave gratings drifting at 13.75 or 27.5 degrees/second. The stimulus spanned 5 or 10 degrees of visual angle and was presented at 10–20 degrees of retinal eccentricity. Useful Field of View (UFOV®) was also assessed in the second and third studies. The first and second studies used a bespoke driving perception questionnaire to measure accident risk, and the second study validated that questionnaire against an abridged Manchester Driver Behaviour Questionnaire. The third study's measure of accident risk was driving simulator performance (i.e., driving examiners' assessments and crash counts). PMCT and UFOV® predicted accident risk equally well. Future work will include development of a practicable two-minute version of the PMCT for use by DMV staff and clinical practitioners.Les conducteurs âgés de 70 ans ou plus ont un taux de collisions aux intersections nettement plus élevé que les conducteurs plus jeunes. Plusieurs de ces accidents s'expliquent par une défaillance relative au repérage d'informations visuelles, ce qui, par conséquent, résulte en une violation du droit de passage du ou des véhicules en approche. Trois études traitant de perception visuelle des mouvements en relation avec les risques d'accidents révèlent que le seuil de contraste dynamique en périphérie visuelle (SCDPV) pour des ondes sinuosidales de basses fréquences spatiales augmente significativement avec l'âge. Soulignons que les résultats au SCDPV expliquent environ 40% de la variance des indices de performance au volant (p < .001). Approximativement vingt conducteurs âgés de 65 ans ou plus ont participé à chaque étude. Dans chacune des trois études, le SCDPV des conducteurs plus âgés a été évalué en utilisant des procédures psychophysiques de choix forcé. Le stimulus consistait en une ondelette sinusoïdale de 0.4 cycle/degré avec un déplacement centripète de 13.75 ou 27.5 degrés/seconde. Le stimulus avait une largeur de 5 ou 10 degrés d'angle visuel et a été présenté à 10 à 20 degrés d'excentricité rétinienne. Un test évaluant l'attention et la vitesse de traitement (Useful Field of View; UFOV®) a également été administré dans la deuxième et la troisième étude. Un questionnaire évaluant le risque d'accident à partir d'items portant sur la perception de la conduite automobile a été développé et utilisé dans la première étude, puis validé dans la seconde par l'intermédiaire du Questionnaire Manchester portant sur les comportements du conducteur (Manchester Driver Behaviour Questionnaire). La troisième étude mesure le risque d'accidents en conduite simulée (c.-à-d., évaluation des réactions au volant par un observateur et nombre total d'accidents). Le SCDPV et le UFOV® ont un pouvoir de prédiction équivalent de la conduite en contexte de simulation. Les travaux futurs incluront le développement d'une version écourtée du SCDPV dans le but d'en promouvoir l'usage par les professionnels et par les autorités en matière de sécurité routière.
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Hackett, Deborah Anne. "Exploring the mechanisms of Rarebit perimetry." Connect to thesis, 2009. http://repository.unimelb.edu.au/10187/5729.
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Visual field testing, or perimetry, measures peripheral visual loss in eye diseases such as glaucoma. Rarebit Perimetry (RBP) is a new and novel perimetric method, introduced in 2002 by Lars Frisén (2002), with the aim of detecting low degrees of neural damage within the retina.RBP is unlike conventional perimetric methods that measure levels of retinal sensitivity, but instead uses very bright (i.e. suprathreshold) and very small targets to detect tiny areas of absolute blindness within otherwise normal areas of vision. RBP thus claims to locate miniscule gaps in the receptive field matrix of neurons in the retina, with the assumption that dead neurons leave gaps in this matrix. The most useful application of this idea is to detect progressive eye disease in the earliest stages (Frisén, 2002). Current research shows that RBP correlates with other standard visual field tests (Brusini, Salvetat, et al., 2005; Frisén, 2003; Gedik, Akman, et al., 2007; Martin & Wanger, 2004), but may afford greater sensitivity by detecting very mild visual losses missed by other tests (Martin, Ley, et al., 2004; Martin & Nilsson, 2007; Nilsson, Wendt, et al., 2007).
To date, there are no studies that definitively test the theoretical basis of RBP, so in this thesis I aim to explore the proposed underlying mechanisms and assumptions of this test. In particular, the proposed mechanism of RBP leads to specific predictions as to how responses will alter when the luminances of the RBP targets are systematically decreased. I therefore compared RBP responses of mean hit rate as a function of target luminance and found results to be inconsistent with the proposed RBP mechanism. Mathematical simulations were performed to explore reasons for the differences between the two groups (Chapter Seven).
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Friström, Björn. "Aspects of the diagnosis and treatment of glaucoma /." Linköping : Univ, 2001. http://www.bibl.liu.se/liupubl/disp/disp2001/med690s.pdf.
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Alencar, Caroline Dias da Costa. "Efeitos da desnutrição proteica na percepção de contraste e acuidade visual em humanos e em ratos." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/47/47135/tde-17032015-124043/.
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O objetivo do presente estudo foi avaliar o efeito da desnutrição proteica em humanos e em modelo animal por meio de medidas comportamentais e bioquímicas. Participaram desse estudo 60 crianças com idade de 7 a 10 anos, sendo 20 eutróficas (grupo controle, GC), 20 com desnutrição atual (grupo experimental atual, GEa) e 20 com desnutrição pregressa (grupo experimental pregresso, GEp). Esses três grupos foram replicados em modelo animal, sendo cada grupo composto por 6 ratos wistar. A acuidade visual (AV) e a sensibilidade ao contraste (SC) foram medidas por meio do método psicofísico em humanos (experimento I) e em ratos (experimento II). Para a medida comportamental com animais foi desenvolvido o Labirinto de Imagens. As análises bioquímicas foram realizadas por meio da técnica de imunohistoquímica e de morfometria da retina de 5 animais de cada grupo (experimento III). Os resultados dos testes comportamentais em humanos e em animais mostraram prejuízos no desempenho dos grupos desnutridos, principalmente no GEp, mesmo com recuperação nutricional. O Labirinto de Imagens se mostrou uma ferramenta útil para medida de parâmetros visuais em roedores. Entretanto, as análises histológicas não apresentaram diferenças significantes entre os grupos, o que provavelmente se deve ao nível de análise não ser capaz de medir componentes sinápticos, arborização dendrítica ou do sistema de neurotransmissãoNot informed by the author
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Diamond, Mark R. "The effect of saccades on visual sensitivity and time perception." University of Western Australia. School of Psychology, 2003. http://theses.library.uwa.edu.au/adt-WU2003.0038.
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Considerable evidence indicates that visual sensitivity is reduced during saccadic eye movement. A central question has been whether saccadic suppression results from a non-visual central signal, or whether the obligate image motion that accompanies saccades is itself sufficient to mask vision. In the first of a series of experiments described here, the visual and non-visual effects of saccades were distinguished by measuring contrast sensitivity to luminance modulated low spatial frequency gratings, at 17 cd·m¯² and 0.17 cd·m¯², in saccade conditions and in conditions in which saccade-like image motion was produced by the rotation of a mirror but when observers’ eyes were kept still. The time course of suppression was examined by making measurements from well before image motion began until well after it had ended. A tenfold decrease in contrast sensitivity was found for luminance-modulated gratings with saccades, but little suppression was found with simulated saccades. Adding high contrast noise to the visual display increased the magnitude and the duration of the suppression during simulated saccades but had little effect on suppression produced by real saccades. At lower luminance, suppression was found to be reduced, and its course shallower than at higher luminance. Simulated saccades produced shallower suppression over a longer time course at both higher and lower luminance. In a second experiment the time course of contrast sensitivity to chromatically modulated gratings, at 17 cd·m¯², was examined. No suppression was found; rather there was some evidence of an enhancement of sensitivity, both before and after saccades, relative to fixation conditions. Differences in the effects of real and simulated saccades in the magnitude and time course of sensitivity loss with luminance modulated gratings suggest that saccadic suppression has an extraretinal component that acts on the magnocellular system; the pattern of enhancement found in the later experiment suggests a selective favouring of the parvocellular system both immediately prior to and immediately after saccades. The possibility that the degree of enhancement in sensitivity varies across the visual field was examined using spatially localized stimuli (either high spatial frequency chromatically modulated gratings or letter combinations). Sensitivity was found to decrease at the initial fixation point during the 75 ms prior to saccadic onset and simultaneously to improve at the saccadic target. In the immediate post-saccadic period, sensitivity at the saccadic target was found to exceed that which had been manifest at the initial fixation point prior to saccades, suggesting that post-saccadic enhancement may improve the temporal contrast between one fixation and the next. The final experiments investigated the possibility that our sense of continuity across saccades (as opposed to stability) is influenced by saccade-induced errors in locating events in time. The results of these experiments suggest that saccades can result in errors in judging (a) the time at which external events occur relative to saccadic onset, (b) the temporal order of visual events, and (c) the magnitude of temporal intervals. It is concluded that apparent time is generally foreshortened prior to saccades. This might be due to selective suppression of magnocellular activity and might function to hide saccades and their effects from our awareness. A speculative synthesis is presented based on the idea that recurrent feedback between the neocortical and cortical structures on the one hand, and the thalamic nuclei on the other, has special importance for perception around the time of saccades
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Lewis, Peter. "Improving Peripheral Vision Through Optical Correction and Stimulus Motion." Doctoral thesis, Linnéuniversitetet, Institutionen för medicin och optometri (MEO), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-52286.
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The loss of central vision subsequent to macular disease is often extremely debilitating. People with central field loss (CFL) must use other peripheral areas of the retina in order to see; areas with inferior resolution capacity, which are also affected by off-axis optical errors. The overall aim of the work encompassed by this thesis was to identify and evaluate methods of improving vision for people with CFL; with focus on the effects of off-axis optical correction and stimulus motion on resolution acuity and contrast sensitivity. Off-axis optical errors were measured using a commercially-available COAS-HD VR open-view aberrometer. We used adaptive psychophysical methods to evaluate grating resolution acuity and contrast sensitivity in the peripheral visual field; drifting gratings were employed to measure the effect of motion on these two measures of visual performance. The effect of sphero-cylindrical correction and stimulus motion on visual performance in healthy eyes and in subjects with CFL was also studied; in addition, the effect of adaptive optics aberration correction was examined in one subject with CFL. The COAS-HD aberrometer provided rapid and reliable measurements of off-axis refractive errors. Correction of these errors gave improvements in low-contrast resolution acuity in subjects with higher amounts of oblique astigmatism. Optical correction also improved high-contrast resolution acuity in most subjects with CFL, but not for healthy subjects. Adaptive optics correction improved both high and low contrast resolution acuity in the preferred retinal locus of a subject with CFL. The effect of stimulus motion depended on spatial frequency; motion of 7.5 Hz improved contrast sensitivity for stimuli of low spatial frequency in healthy and CFL subjects. Motion of 15 Hz had little effect on contrast sensitivity for low spatial frequency but resulted in reduced contrast sensitivity for higher spatial frequencies in healthy subjects. Finally, high-contrast resolution acuity was relatively insensitive to stimulus motion in the periphery. This thesis has served to broaden the knowledge regarding peripheral optical errors, stimulus motion and their effects on visual function, both in healthy subjects and in people with CFL. Overall it has shown that correction of off-axis refractive errors is important for optimizing peripheral vision in subjects with CFL; the use of an open-view aberrometer simplifies the determination of these errors. In addition, moderate stimulus motion can have a beneficial effect on contrast sensitivity for objects of predominantly low spatial frequency.
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Reinhardt, Juliane [Verfasser], and Christian G. [Akademischer Betreuer] Schroer. "Resonant Hard X-ray Ptychography for High-Sensitivity Imaging with Chemical Contrast / Juliane Reinhardt ; Betreuer: Christian G. Schroer." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2017. http://d-nb.info/1139493051/34.
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Klein, Johann Oliver. "Contrast sensitivity loss in patients presenting with cataract and early stage glaucoma using methods suitable for clinical use." Thesis, Ulster University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.646850.
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Glaucoma is an insidious progressive disease that leads to a permanent loss of vision if left untreated. The development of methods for early detection of the disease is essential as early diagnosis and treatment significantly reduces the risk of sight loss. Contrast sensitivity (CS) testing has shown the potential to detect glaucoma in its early stage. However, as glaucoma is mainly a disease of the elderly, comorbidity with cataract is common. The extent to which cataractous changes in glaucoma patients affect grating CS tests and how these effects depend on the type and severity of cataract is not known. This study aimed to investigate CS loss in glaucoma and cataract patients and to assess whether these tests could provide the basis for improved clinical diagnosis. The study demonstrates that grating CS tests can be performed using TFT flat panel monitors which are largely available in clinical settings after appropriate measurements to show the suitability of each particular monitor for visual research . The thesis presents experimental evidence that CS for both stationary and flickering gratings is significantly reduced in patients with early glaucoma and cataract when compared to age-matched controls with cataract. This suggests that both tests can separate neural and optical loss and are thus sensitive methods for early glaucoma detection in the presence of a cataract. The results of this thesis show that grating CS is not only a sensitive test for early glaucoma detection but might also be a useful tool for monitoring the disease. Finally, this thesis shows that glaucoma patients experience significant glare which is related to the disease severity as characterised by optic disc topography. In conclusion, this work has shown that CS testing with stationary and/or flickering gratings is capable of differentiating patients with glaucoma from cataract controls and that such a testing procedure can be easily implemented in clinical practice using TFT flat panel monitors.
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Skinner, Fiona K. "Dopamine and visual function in schizophrenia : a psychophysical investigation using the tilt after-effect and contrast sensitivity tests." Thesis, University of Aberdeen, 1994. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU068528.
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The study used a non-invasive technique, the Tilt Aftereffect (TAE) test, to investigate the visual changes influenced by dopamine (DA) in schizophrenia. One-third of forty five schizophrenic patients could not complete the TAE test and this group was found to have impaired sustained attention and to have different demographic and clinical characteristics from the schizophrenic patients who could complete the TAE test. TAE changes were found only in response to DA changes brought about by altering neuroleptic levels, e.g. 'before' compared with 'after' a depot injection. These changes were only found when gratings of 2 c/d were used and not for 10 c/d. No illness or drug effect was found using the TAE test. A similarity in the pattern of change over time was found for the TAE test using 2 c/d gratings and the peak spatial frequency (SF) from the Contrast Sensitivity (CS) test in response to changes in levels of DA. A decrease in DA caused a shift of the CS peak to lower SFs, with a decrease in sensitivity for mid to high SFs (3 - 10 c/d) and an increase in sensitivity for low SFs (0.5, 1 c/d). The findings suggest that both the TAE and CS tests are influenced by DA and that lateral inhibition alone cannot explain the production of the TAE since the influence of the orientation of the adapting gratings on the size of the TAE indicates that an adaptation process is involved. It is suggested that the transient system, which is sensitive to low spatial and high temporal frequencies, may be selectively affected by DA changes.