Ana Ramirez¹ (), Curtis Baker¹, Ari Rosenberg²; ¹McGill University, ²University of Wisconsin-Madison

Parasol, Y-like retinal ganglion cells (RGCs) are functionally distinct in that they respond nonlinearly to high spatial frequencies (SFs) and temporal frequencies (TFs). Neurophysiology has indicated that cat Y-cells prefer orientations aligned with the area centralis, which is analogous to the fovea. Contrast-modulation (CM) stimuli (high-SF carrier gratings contrast modulated by a low-SF sinewave envelope) selectively engage the nonlinear mechanisms of Y-like RGCs which initiate the magnocellular pathway. Thus, CM stimuli offer a promising tool for probing magnocellular function in pathologies such as glaucoma. Human visual fields (VFs) measured with simple gratings typically show high foveal sensitivity and polar-angle asymmetries. Previous human psychophysics demonstrated that CM motion performance varies little with eccentricity. Here we investigate whether CM motion performance in humans shows fovea-aligned orientation biases for the carrier, and whether CM motion performance reveals VF asymmetries. Achromatic CM stimuli were presented on a CRT display and viewed monocularly. The stimuli consisted of a sinewave-grating envelope (0.50 cpd) drifting at 3 Hz, which modulated the contrast of a high-SF sinewave carrier (6 cpd) flickering at 15 Hz, with envelope and carrier contrasts of 80-100%. The stimuli were presented at 8 polar locations, 4.3 deg eccentricity from fixation. Observers reported the direction of CM envelope motion on each trial (2afc button-press). Envelope motion direction discrimination performance was measured for 4 carrier orientations at each VF location. The results show CM envelope motion performance that varied systematically with carrier orientation, with the optimal orientation often aligned towards the fovea. Performance was better in the lower than upper VF. There was not a clear horizontal-vertical anisotropy. These findings indicate that CM perimetry may exhibit fovea-aligned orientation biases consistent with Y-like processing, while the VF dependence might exhibit some polar angle asymmetries as seen for simple sinewave gratings.

Acknowledgements: Canadian NSERC (RGPIN-2023-03559) to CB. National Institutes of Health Grants (EY029438 & EY035005) to AR.