Fig. 6. Absolute sensitivity as a function of background level and retinal eccentricity. At moderate and high levels of background, sensitivity is highest at the fovea. At low levels of background, a depression of sensitivity is present at the fovea. (Auhlhorn E: Über die Bezeihung zwischen Lichtsinn und Sehasharfe. Graef's Arch Ophthalmol 167:4, 1964.)