Figure 3. Modeling the V1–V2–V3 complex.

(a) The visual field, i.e. the starting point of the model. (b) In a first step as suggested by Balasubramanian et al. (2002) [2], the visual field is transformed by simple reflections into an intermediate space, which, in a second step (c), is projected to cortical space using the classical log-polar function. Note that projected size increases dramatically near the foveal projection with increasing polar position. This effect is maximal for eccentricity ranges around a = 1.05°. The two areas marked with a star represent the same part of the visual field, but the representation is significantly larger in V3 (blue) than in V1 (red). This expansion is not supported by reported data [15],[27] (d) The Double-Sech model corrects this undesirable behavior. V2 and V3 maintain a constant size ratio to V1 throughout all eccentricities. In the Double-Sech model, the surface area relation between V1–V3 is simply specified by the ratio of the α₁–α₃ parameters. In the example illustrated here, α₃ = 0.4 for V3 while α₁ = 1 for V1. Accordingly, the area ratio is V3∶V1 is 0.4∶1.