The outcome that is called vision is a product of a great many factors both broad and pervasive throughout the organism and peculiarly dependent upon specific tissues. No ordinary treatment can even touch on all of these factors. Some of them are possibly yet unknown, and a few of them, although known, have not yet been given much attention. It is this borderline of the known and the unknown and the littledealt-with to which I am going to give some consideration in what I have to say. I shall discuss briefly four items: (1) the alternation of response theory; (2) brightness enhancement; (3) some factors underlying sensory fusion from intermittent stimulation; and (4) the nature of the distribution of photic radiation on the retina. Naturally, the four items are not mutually independent and certain of their interrelations will be brought out.
The first and third items have to do with