Changes in visual computations across the visual field: depth and crowding

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The centre of our visual field (the fovea) has the highest ability to resolve fine details (acuity), and if we notice something of interest in our surroundings we will move our eyes so that the image of the object falls on the fovea, rather than some peripheral part of our retinas. We do this because our visual systems have low acuity away from the fovea. If is often surprising how few letters on a page we are able to identify as their distance from the fovea (eccentricity) increases. For many years vision scientists have studied peripheral vision and verified that visual acuity falls off as stimuli are presented at increasing eccentricities. This can be done by having observers fixate at a point on computer monitor, and then flashing a stimulus in the periphery so that they don't have time to move their eyes to look directly at it. It has been found, however, that in many cases, when peripherally presented stimuli are made sufficiently large (magnified relative to a foveal standard), observers can be as accurate at making judgments about the magnified stimuli as they are about the standard stimuli presented to the fovea. For many years the stimuli used in experiments of this sort have been simple geometric forms (lines and letters) and little attention has been paid to whether stimulus magnification allows us to detect small differences the the three-dimensional shapes of objects, the direction that person is walking or even the identity of walkers. A large portion of the research proposed here deals with exactly this kind of question. Specifically, we asked whether stimulus magnification permits us to make judgements about 3D shapes in the periphery that are as accurate as those we can make at the fovea. We ask about this ability both for stimuli isolated in the visual field, or surrounded by flanking items at varying distances, because it is well know that identifying stimuli in a crowded background is much harder in the periphery than at fixation. Although our interests are theoretical, in the long run a better understanding of the abilities of peripheral vision will put us in a better position to help those who have lost foveal vision because of diseases like macular degeneration.