The relation of size of stimulus and intensity in the human eye: II. Intensity thresholds for red and violet light.

Abstract

Intensity thresholds for red and violet light as a function of the area of the stimulating surface were detd. for the periphery of the human eye. Measurements with red light were made on the fovea. Under the conditions of stimulation used in this expt. the intensity thresholds for both fovea and periphery followed a typical course with an increase in area. The intensity threshold was high for small areas and decreased as area increased, until with larger areas it approached a final, limiting value. The curves obtained on the periphery for red and violet were parallel along the log threshold axis. This was interpreted to mean that no cones were involved with either type of stimulation. The results were described by an hypothesis developed in an earlier paper and by one which considered the photochemical activity of the single retinal receptive unit.