Literature about two illusions that are traditionally linked to lateral inhibitory processes in the retina is surveyed. Despite much research and a long history, the Mach bands illusion has not yet been very well-understood. Quantitative data is lacking, while qualitative data is controversial. The Hennann Grid illusion, equally old, has not yet been fully explored either. A critical and a comparative review of the experiments and the conclusions is carried out, noting common results as well as contradictory ones. New experiments and a different method of measurement are then proposed. Some preliminary experiments and their results are included in the appendix together with a review of recent knowledge about the primate retina and its functioning. / Master of Science

Indiana University-Purdue University Indianapolis (IUPUI) / Photoreceptors are a class of sensory neuronal cells that are deleteriously affected in many disorders and injuries of the visual system. Significant injury or loss of these cells often results in a partial or complete loss of vision. While previous studies have determined many necessary components of the gene regulatory network governing the establishment, development, and maintenance of these cells, the necessary and sufficient profile and timecourse of gene expression and/or silencing has yet to be elucidated. Arduous protocols do exist to derive photoreceptors in vitro utilizing pluripotent stem cells, but only recently have been able to yield cells that are disease- and/or patient-specific. The discovery that mammalian somatic cells can be directly reprogrammed to another terminally-differentiated cell phenotype has inspired an explosion of research demonstrating the successful genetic reprogramming of one cell type to another, a process which is typically both more timely and efficient than those used to derive the same cells from pluripotent stem cell sources. Therefore, the emphasis of this study was to establish a novel system to be used to determine a minimal transcriptional network capable of directly reprogramming mouse embryonic fibroblasts (MEFs) to rod photoreceptors. The tools, assays, and experimental design chosen and established herein were designed and characterized to facilitate this determination, and preliminary data demonstrated the utility of this approach for accomplishing this aim.