George Sperling¹ (), Lingyu Gan²; ¹University of California, Irvine, ²University of California, Irvine

Gan and Sperling, Journal of Vision, 2025, tested foveal grating acuity limits for red/yellow and green/yellow chromatic and for yellow/yellow monochromatic gratings, all > 30 cycles/deg. They found found three classes of subjects: Some almost exclusively used the red stimulus component for acuity judgments, some used the green, some equally red and green components. Yellow/yellow luminance judgments were generally inferior to chromatic judgments except for red dominant subjects judging red-yellow gratings in which the component stripes were of similar intensities. For the three classes of subject, when there was a clear acuity minimum as a function of the intensity of variable color stripes, it occurred when the energy of the red-or-green color stripes equaled the energy of only that same color component in the yellow stripes. That acuity minima occurred at minimal selective color differences despite large between-stripe luminance differences was evidence for superior color-selective versus luminance foveal acuity processing. Here we test whether similar procedures in peripheral viewing can reveal magno-selective versus parvo-selective processing. One subject from each color-dominance class viewed peripheral high-spatial-frequency gratings (8.9-11.7 cycles/deg). To avoid eye movements, acuity gratings appeared randomly 6.5 deg to right or left of fixation for 100 msec. Subjects judged grating orientation for a full range of contrasts of the variable-color grating stripe. In a related task, subjects judged the motion direction of similarly-colored gratings moving at 12.5 Hz, a pure magno task. Unlike the foveal data, the peripheral motion contrast minima and grating minima perfectly coincided, demonstrating magno-system processing for 100 msec high-resolution peripheral gratings and for 12.5 Hz high-frequency motion stimuli for all three subject types. Conclusion: The grating acuity paradigm reveals parvo-system properties when the parvo system is used (0.5 sec, foveally) and magno-system properties when it is used (0.1 sec, 6.5 deg peripherally).