A psychophysical and electrophysiological study of light adaptation.

Abstract

Two light-adaptation phenomena, previously isolated at photopic adapting levels are shown to hold also at scotopic adapting luminances. These are: (a) The "Crawford effect," where the threshold to a test flash is raised when it closely precedes an adapting stimulus; (b) a secondary decrease in the intensity-discrimination threshold, which follows the initial increase. Electrophysiological erg. data are also given which help support the interpretation that the initial time course of light adaptation, as measured by the intensity-discrimination threshold, has a non-photochemical basis, and that the "Crawford effect" is the result of an interaction between physiological response processes associated with the test and adapting stimuli.