Maisha Tahsin Orthy¹, Hunter Finney¹, Jeanine Stefanucci¹, Bobby Bodenheimer², Sarah Creem-Regehr¹; ¹University of Utah, ²Vanderbilt University

People with low vision, those with uncorrectable vision loss who rely on residual vision, represent a rapidly growing global population. Peripheral visual field loss (PVL) is caused by conditions such as retinitis pigmentosa and glaucoma, which can impair spatial layout perception, obstacle detection, and locomotor guidance. Peripheral vision is essential for action-related tasks as well as affordance perception. We found previously that simulated PVL led observers to underestimate their perceived capabilities to step over gaps relative to no vision loss. However, low vision is also sensitive to contrast-related deficits, especially under low illumination, which may compromise the detection of boundaries or terrain features necessary for safe movement. The present research investigated whether environmental illumination modulates gap-affordance judgments under simulated PVL. Twelve participants with normal vision judged their gap-stepping affordances in virtual reality (VR) while wearing an eye-tracked head-mounted display that simulated PVL (tunnel vision), resulting in a field of view of about 26 degrees. Participants viewed an urban scene with gaps on the ground ranging from 0.55 to 1.6 m presented randomly under blocks of trials in bright and low illumination. For each trial (24 total in each block), participants made a binary yes/no judgment, rated confidence on the judgment, and their response time was recorded. Gap width judgments were scaled to individual leg length and modeled using binomial logistic regression. Contrary to our hypothesis, lighting conditions did not significantly affect affordance judgments; participants showed similar transition thresholds and confidence ratings in bright and low light. However, response times were slower in the low-light condition, suggesting increased perceptual or decisional uncertainty that did not translate into altered action boundaries. These results indicate that simulated PVL may reduce overall visual efficiency under dim light without affecting perceived affordances. Future work will test clinical low-vision populations and explore additional environmental variables.