Performance of inhomogeneous and anisotropic filters in the visual system.

Inhomogeneous and anisotropic processing stages developed in the visual system during evolution in order to match a (certainly highly complex) biological optimality criterion. As the examples presented in this paper show, scenes viewed can be separated according to their information content with filter stages such as processing of the central area of the picture field in a wide band fashion, where each detail is perceived and the contrasts are amplified. This requires good illumination as the amplification is small. At the periphery the amplification is higher which favors twilight vision. Especially the sensitivity for moving patterns is highly developed and a band pass prefilter requires only spatially narrow band channels in the course of further processing. Direction specific filter stages make it possible to solve special problems such as the reconstruction of a form from an illuminance distribution.