The relation of size of stimulus and intensity in the human eye: I. Intensity thresholds for white light.

Abstract

An apparatus and procedure are described which make it possible to obtain reproducible intensity thresholds for varying sizes of illuminated areas in the human eye. Intensity thresholds follow a typical course with an increase in area in both the periphery and fovea of the eye. In both regions the intensity threshold is high for small areas. As area increases, the threshold decreases until with large areas it approaches a final, limiting value. In the fovea, the decrease of threshold with increase in area takes place within the confines of a stimulus diam. of about 1 degree. In the periphery, the final level is nearly attained at a diam. of 10 degrees. A quantitative account of the area-intensity relation is given. This describes the data over the total range of area in the fovea. In the periphery, it holds for areas having diams. greater than 20 minutes.