Krishnaveni Nagarajan¹, Martina Poletti²; ¹Department of Brain and Cognitive Sciences, University of Rochester, ²Department of Brain and Cognitive Sciences, Neuroscience, Center for Visual Science, University of Rochester

Foveola, central 1° of the retina, contains the highest cone density and supports high-acuity vision. Our previous work showed that under diffraction limited viewing, subjects establish an alternative preferred locus of fixation even when visual occlusions are limited to a region of just 0.2 deg in diameter around the gaze center. However, it remains unclear whether a similar restructuring of fixation behavior occurs under natural optics and how rapidly such adaptation unfolds. Six emmetropic observers performed a 4AFC orientation-discrimination task with tumbling-E optotypes (1.25 arcmin stroke-width; 20/25 equivalent acuity). Each trial was preceded by a self-paced fixation period on a blank display. A simulated central scotoma, implemented as a flat-top Gaussian mask (σ ~ 2.0 arcmin) with a fully opaque center (~3.8 arcmin diameter), rendered gaze-contingently at the observer’s preferred locus of fixation using a high-precision digital dual-Purkinje image eye tracker. The task was first completed under normal viewing and then repeated across three sessions in the presence of the simulated scotoma. Overall, visual discrimination performance was reduced by the scotoma (Mean ± SD: 87.61 ± 7.89% vs. 69.78 ± 13.86%, p = 0.031), but improved systematically over a short time, consistent with short-term functional adaptation (p = 0.011). Comparisons of trial-wise fixation centroids revealed significant, idiosyncratic shifts in gaze position for all participants (p < 0.05), with 68% gaze-position contour centroids displaced by ~4 arcmin between baseline and scotoma condition. These shifts emerged already during the initial self-paced fixation period, confirming the recruitment of an alternate retinal locus of fixation, right outside scotoma’s opaque zone. These findings indicate that even subtle disruptions of central vision, as small as 0.2° are sufficient to alter both high-acuity performance and fine oculomotor behavior under normal viewing conditions, and that observers can begin to reorganize fixation patterns over just a few experimental sessions.

Acknowledgements: This work was funded by NIH Grant EY029788 to MP and NIH grant EY001319 to the Center for Visual Science