Figure 4.

The human optical condition in a Savannah landscape. Notice that visual ray A hits the soil, whereas visual ray B is intercepted by the vegetation. The light ray from the distant mountain Q never makes it to the eye because it is scattered out of the beam. (Notice that “light” and “visual” rays have opposite directions!) In contradistinction, the light ray from the sun P is scattered into the beam and reaches the eye from the direction of the mountain. The sky canopy fills the upper part of the visual field. This simple scheme captures most of the relevant optics of an early human Umwelt (von Uexküll, 1921).