Intensity discrimination and its relation to the adaptation of the eye

UNDER the above title Wright [1935] has recently published measurements which describe the influence of pre-adapting the eye to high intensities on its capacity to discriminate differences between lower intensities. Wright states that he is unable to describe these measurements in terms of the visual receptor process, and therefore concludes that the basis for intensity discrimination cannot be in the receptor process but must be in some undefined, but more centrally located series of events. In particular, Wright singles out our ideas [Hecht, 1934a] about the nature of the receptor process in the retina, and states that in terms of his new data "the experimental support for" these ideas "has thus largely disappeared ". Examination of existing data on intensity discrimination and their relation to the photoreceptor process shows that (a) Wright has missed the meaning of his own measurements; actually they demonstrate almost the opposite of what he supposes; and (b) his measurements are easily described in terms of equations already derived for the receptor process in the retina. The two conclusions of Wright's paper are therefore not valid. II. INTENSITY DISCRIMINATION.