Abstract
People who lose their central visual field in both eyes often adopt a peripheral retinal region, the preferred retinal locus (PRL), for seeing. Although the progression of vision loss is often asymmetrical between the two eyes, little is known about how an adopted PRL responds to changes in the central scotoma in one eye. In this study, we used a gaze-contingent paradigm to simulate the presence of central scotomas in the two eyes and examined how a “PRL” might change in response to the enlargement of the simulated scotoma in one eye. We used a stereoscope that allowed us to present a gaze-contingent artificial scotoma in the two eyes separately. During the initial training, a visible scotoma of identical size (4° in diameter) was presented in each eye of five normally sighted subjects who were instructed to make saccades to search for a Tumbling-E stimulus that appeared randomly on the screen, and to identify its orientation. All subjects developed a “PRL” after 1500~5000 trials. Fixation stability improved and reached an asymptote over time. Immediately following the initial training, we doubled the size of the artificial scotoma in one eye (becoming 8°); and subjects performed the same task of identifying the orientation of the E-stimulus (letter size was enlarged). With visible scotomas, subjects were able to use the initially developed “PRL” to perform the task, with the fixation stability remaining at the initially reached asymptote. The trend was similar with invisible scotomas, despite a slight increase in fixation instability and “PRL” location variability. No difference was evident between the two eyes in either the “PRL” location or fixation stability. Our results suggest that, rather than pushing the “PRL” outward in response to the increased scotoma size in one eye, subjects rely on the “PRL” in their better eye for visual tasks.