Project Summary/Abstract Visual Snow Syndrome (VSS) is a serious but poorly understood visual disorder characterized by the persistent perception of specks flickering across the entire visual field, akin to television snow. VSS has an estimated prevalence of 1.4-3.3% and is often accompanied by additional symptoms such as prominent afterimages (palinopsia), poor night vision, entoptic phenomena, and photophobia (light sensitivity). These symptoms make tasks like reading and driving particularly difficult. While previous research has focused on identifying the common symptoms and comorbidities, effective treatments have not been identified, the mechanisms underlying the disorder are still unknown, and quantitative assessments of visual perception remain sparse. The proposed research seeks to address these knowledge gaps by measuring differences in visual performance and associated neural processing with a series of well-established psychophysical and imaging paradigms. To provide quantitative measures of perception and visual processing in VSS, we will assess (1) contrast sensitivity, (2) spatial context, and (3) temporal context perception in people with VSS compared to normally sighted controls through a series of fundamental psychophysical and high field (7T) functional magnetic resonance imaging (fMRI) experiments. These experiments will help us understand how people with VSS perceive and process contrast, which is an important measure of visual function that is related to performance on every-day visual tasks. Additionally, the proposed research will address how both spatial and temporal context are altered in VSS—previous but sparse research suggests that both spatial and temporal context may be altered in VSS, but further evidence with both larger numbers of participants and robust measures of neural activity are required to investigate potential differences in visual context processing. Critically, we will also provide high resolution 7T fMRI measures of cortical responses during visual tasks to investigate potential differences in gain control throughout the visual system. The proposed assessment of visual perception and accompanying measurements of neural processing in VSS are necessary to better characterize this disorder, and will help formulate hypotheses about mechanisms underlying VSS.