Border contrast as a function of retinal locus

When the visibility of a small test spot was measured by direct brightness matching at various locations along the white edge of a black and white border, it was found that the white background was perceived as becoming progessively brighter as the border was approached. The effect was greater when a corner was neared. Moreover, greater effects, i.e., larger differences between the edge effect and base level (no border) were found at distances farther removed from the fovea (0 deg 12 min to 3 deg 52 min).