A Theoretical Basis for Intensity Discrimination in Vision

Abstract

A theory of visual intensity discrimination is proposed which describes quantitatively all the established, available data from the photosensory systems possessed by such diverse animals as the clam, Mya; the insects, Drosophila and the bee; and the human eye. The theory depends on the photochemical events which take place at the moment when a photosensory system already adapted to the intensity [image] is exposed to the just perceptibly higher intensity [image] +[LAMBDA][image]. Unlike previous formulations, this theory predicts that the fraction [LAMBDA][image]/[image], after rapidly decreasing as 7 increases, does not increase again at high intensities, but reaches a constant value which is maintained even at the highest intensities.