Fig. 2

a Retinal grid which serves as a reference frame in the Lagrangian formulation of retinotopy. In the inner 9^∘, iso-eccentricity lines are drawn in 1^∘-steps in green. From 10^∘ to 90^∘ iso-eccentricity lines are drawn in 10^∘-steps in blue. Meridians are drawn in 15^∘-steps in red. b The neural representation of the retinal grid mapped with Eq. 3 serves as a flat model of V1. c The blue surface serves as a curved model of V1. It is created by forming b with lift functions (see Fig. 1g and h) in the third dimension. The neural representation of the retinal grid on this surface is placed such that meridians are equidistantly spaced