Rania Ezzo^1,2 (), Marisa Carrasco², Jonathan Winawer², Bas Rokers^1,2; ¹New York University Abu Dhabi, ²New York University

Background: Discrimination of visual motion is direction-dependent: thresholds are lower for cardinal than oblique and for radial than tangential motion (Ezzo et al., 2024, JoV). Using fMRI, we asked whether there are corresponding asymmetries in BOLD amplitude, and whether they are amplified or reduced when local direction matches the global stimulus configuration. Methods: We recorded fMRI BOLD responses to stationary and moving gratings (12º radius) within two global configurations: Cartesian (horizontal, vertical, and left/right-leaning obliques) and Polar (pinwheel, annular, and clockwise/counterclockwise spirals). For each global configuration, responses were measured for the 4 stationary patterns and the 8 motion directions perpendicular to the orientations. Stimuli were approximately matched locally across the two configurations; e.g., for a receptive field centered at +6º on the vertical meridian, the rightward moving vertical grating and clockwise rotating pinwheel matched locally. Thus we could assess the two local motion asymmetries, cardinal vs. oblique and radial vs. tangential, in each global configuration. Using retinotopy, we defined population receptive fields in V1 and MT (“hMT+”), and analyzed data within a 4–8º eccentricity ring. Motion-specific responses were defined as BOLD amplitude for the difference between the moving and matched stationary patterns. Cardinal vs oblique motion: In the Cartesian configuration, BOLD responses to cardinal motion were larger than to oblique motion, by 10% in V1 and 15% in MT. In the Polar configuration, this effect diminished in V1 and approached zero in MT. Radial vs tangential motion: In the Polar configuration, radial motion evoked greater responses than tangential motion, 104% larger in V1 and 24% in MT. In the Cartesian configuration, this radial > tangential effect weakened in V1 and disappeared in MT. Conclusion: Neural responses to motion vary with direction, and these asymmetries are amplified when the local directions are congruent with the global configuration.

Acknowledgements: (1) US NIH National Eye Institute R01-EY027401 to MC and JW, (2) NYUAD Center for Brain and Health, funded by Tamkeen NYU Abu Dhabi Research Institute #CG012 to BR, (3) ASPIRE Precision Medicine Research Institute Abu Dhabi (ASPIREPMRIAD) #VRI-20-10 to BR and (4) Global PhD Fellowship, NYUAD to RE