The relation of size of stimulus and intensity in the human eye: III. The influence of area on foveal intensity discrimination.

Abstract

Foveal in-tensity discrimination thresholds were obtained with white light over a range of 4.6 log units of adapting intensity (I) and for circular areas varying in radius from 2 to 28 mins. of visual angle. With a constant area of stimulus surface, the ratio [DELTA] I/I has a high value for low intensities of I. As I increases, [DELTA] I/I decreases and finally reaches a limiting value at a high level of adapting intensity. At comparable levels of adapting intensity, I, the ratio [DELTA] I/I is large for small areas and decreases as area increases. The results are described by means of a combination of hypotheses one in terms of retinal photochemistry and the other in terms of visual spatial effects.