Fig. 1: The rationale for pRF estimation using radially and tangentially oriented gratings to evaluate the respective influences of topographic factors on the spatial representation of EVC.

a, b Schematic illustrations of two hypothetical factors, co-axiality (a) and radiality (b), that govern the anisotropy of individual RFs of orientation-tuned neurons in the presence of a strong correlation between their orientation preference and polar-angle position. The fixation location is marked by crosshairs. Each cluster of colored dots represents orientation columns that are aggregated within a voxel representing a specific retinotopic position. The colors represent orientation preference, and their distributional biases reflect the strong correlation between columns’ preferred orientation and polar-angle position. The ellipsoids surrounding the dot clusters represent the topographical anisotropy of neurons’ RFs. If co-axiality governs, the RFs are elongated along their preferred orientation (a). If radiality governs, the RFs are elongated along the radial axis (b). c Visual inputs with radially (top) and tangentially (bottom) oriented gratings. d The neural drives by the gratings shown in c. e, f Illustrations of how the same neural drives shown in d induce different neural spatial extents depending on how strongly radiality and co-axiality govern the RF anisotropy. If only co-axiality influences the anisotropy, the neural spatial extent will be co-axially elongated, while the degree of co-axial elongation will not differ between the two orientation conditions (e, left). If co-axiality has a stronger influence on anisotropy than radiality, the neural spatial extent will be elongated in the co-axial direction, with a relatively high degree of elongation in the radial orientation condition (e, right). If only radiality influences the anisotropy, the neural spatial extent will be radially elongated, while the degree of radial elongation will not differ between the two orientation conditions (f, left). If radiality has a stronger influence on anisotropy than co-axiality, the neural spatial extent will be elongated in the radial direction, with a relatively high degree of elongation in the radial orientation condition (f, right).