A series of empirical studies is presented that examine the contribution of Fragile X Mental Retardation 1 (FMR1) gene expression to the structure and function of the visual system. This contribution is documented using a histological approach in human and nonhuman primate tissue in conjunction with psychophysical testing of Fragile X Syndrome affected patients who are lacking FMR1 expression. / In the first set of experiments, immunohistological studies of unaffected human and primate brain tissue were carried out to reveal the staining pattern for Fragile X Mental Retardation Protein (FMRP), the protein product of the FMR1 gene, within the two main subcortical pathways at the level of the lateral geniculate nucleus (LGN). FMRP is expressed in significantly greater quantity within the magnocellular (M) neurons of the LGN when compared to levels obtained from the parvocellular (P) neurons. This finding suggests that M neurons depend on FMRP to greater extent than P neurons for determining their normal structure and function. A subsequent histological analysis of the LGN from a FXS affected individual revealed atypical LGN composed of small-sized neurons that were more P- than M-like. This result supports the notion that with the lack of FMR1 expression as occurs in FXS, the impact is greatest to M neuron morphology. / A second set of experiments explored the idea that the M neuron pathology in FXS results in a functional deficit for processing of visual information carried by this pathway. Detection thresholds for stimuli known to probe either M or P-pathway integrity were obtained from individuals affected by FXS as well as age- and developmental-matched control participants. In support of this hypothesis, FXS affected individuals displayed significantly elevated thresholds for M-but not P-specific achromatic visual stimuli. The selectivity of this deficit was verified in a consequent experiment that evaluated colour vision, a visual attribute known to be exclusively processed by the P-pathway. Affected individuals did not differ significantly from developmental-matched control participants in their ability to detect chromatic stimuli. Finally, the effect of the M pathway deficit on cortical visual function was assessed. Results of these experiments reveal that the thresholds for detection of coherent motion, but not form, are significantly elevated in the FXS group. This finding suggests that the parietal (dorsal) visual stream, the major cortical recipient of input from the M pathway, is detrimentally affected in FXS. / A third experiment examines the extent to which the M pathway deficit impacts on cortical visual functioning by employing stimuli of varying complexity that probe the parietal (dorsal) and temporal (ventral) visual streams separately. Results suggest that FXS affected individuals have a pervasive deficit in their ability to detect both simple and more complex forms of motion. In contrast, these same individuals have normal detection thresholds for simple form stimuli. However, with more complex form stimuli affected individuals have significant elevations in threshold. Taken together these results support the notion that the M pathway deficit is amplified at higher levels of visual processing and further, that FXS affected individuals have difficulties integrating all early visual information.

Thesis (Ph. D.)--University of Wyoming, 2005. / Title from PDF title page (viewed on Oct. 10, 2007). Includes bibliographical references (p. 93-98).

Thesis (Ph.D.)--Drexel University, 2008. / Includes abstract and vita. Includes bibliographical references (leaves 149-157).

This thesis illuminates the phenomenon of the emergent needs post-grief experienced by Adventitiously Visually Impaired (AVI) adults following loss of sight. The research focuses on specific experiential areas related to the phenomenon; the perspectives the AVI adults have of their loss of sight; their experience of grief as a resolvable or chronic process; the emergent psychological, emotional and practical needs they experience; and the support from society, families and rehabilitation in meeting their needs. The influence of the length of time of the impairment on these experiences is also considered. The literature survey indicates that most research on Adventitious Visual Impairment (VI) concentrates on the period before and immediately after rehabilitation, and emphasises practical, technological and technical needs and issues. This focus is limited in acquiring insight and understanding about the psychological and emotional reactions and needs of AVI adults throughout the time course of their impairments. This study applies an adapted phenomenological research strategy using 10 case studies of adults, AVI within and beyond 6 years, to understand the researched phenomenon. Essential insight gained from the study is that loss of sight is an unique experience which is inextricably linked to the degree of vision loss, that many unique but also common psychological, emotional and practical needs are experienced, and that length of time of the VI has a profound impact on these needs and the experience of the grief process. This research challenges the traditional resolvable grief theory and emphasises a chronic, recurrent and episodic grief process. These contrasting processes impact on experienced needs. The research challenges the linear and invariant notion of Maslow's (1987) Need Hierarchy, and emphasises both ascent and descent and simultaneous experiences of unsatisfied needs on different levels of the hierarchy. The research highlights the need for society to know and understand the complex real world of Adventitious VI with all its diverse implications, limitations and needs. As always, there are more questions than answers, but this research provides further insight into the complex real world of Adventitious VI. / Psychology / D. Litt. et Phil. (Psychology)

M.Phil. (Optometry) / The purpose of this study was to determine the prevalence of vision deficiencies in the children from the schools of the learning disabled compared to the children from the mainstream schools. One hundred and twelve (N = 112) children from the two learning disabled schools and eighty (N = 80) children from the mainstream school, in Johannesburg had their vision assessed. The evaluation of functional vision included visual acuity (Snellen Acuity), refractive status (Static Retinoscopy), ocular health status (Internal and External evaluations), accommodation (Monocular Estimate Method (MEM), ±2.00D Flippers, Donder's push up method), binocularity (Cover Test, Vergence Facility, Smooth Vergences, Near Point of Convergence (NPC) and ocular motilities (Direct Observation). The results of this study revealed a significant relationship of poor vergence facility (Cramer's V =0.369); lead of accommodation of the right (Cramer's V = 0.379) and left eye (Cramer's V= 0.386); poor amplitude of accommodation of the left eye (Cramer's V=0.316) and the mainstream group. A significant relationship was found between the learning disabled group and poor saccadic accuracy (Cramer's V=0.343) and a high lag of accommodation of the right (Cramer's V= 0.379) and the left eye (Cramer's V= 0.386). Both the learner groups in the current study present with different visual deficiencies, and thus comparisons in terms of prevalence is complicated. It will be erroneous to say one group presents with a high prevalence of visual deficiencies than the other nor to conclude that the prevalence of visual deficiencies is the same in both groups. The results of this study provide further support for full vision screenings (including visual integrity pathway, and visual efficiency skills) to be routinely done in both mainstream and schools for the learning disabled.

No description available.

No description available.

No description available.

by Sun-on Chan. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1988. / Bibliography: leaves 132-157.

published_or_final_version / Psychology / Master / Master of Philosophy