The relation of border-contrast to the distinctness of vision.

Some factors in brightness discrimination.

“…When dimmer they progressively increase the acuity as size increases. Their size is indifferent when they are the same brightness as the test object (17).…”

“…Since large surroundings extending to at least twenty degrees are effective in determining both visual acuity and the plateau or drop of C.F.F. at high intensities, the idea of some kind of a chemical intensifier has been developed to account for this action (14,17,34). That neural interaction beyond four degrees takes place in the eye is given support by Adrian and Matthews in their experiments on the excised eel's eye.…”

Some parallels between pupillary 'reflexes' and brightness discrimination.

“…(4) The stimulation of one eye with a disc whose intensity is varied from dim to bright, following which the corresponding area in the other eye is also stimulated by a similar disc whose intensity likewise begins at a very low level and is increased to the level of the first. (5) The use of the same procedure on non-corresponding points of the two eyes. (6) The use of the same procedure on two areas of one retina.…”