Wavelength variation in directional sensitivity of the long- and medium-wave sensitive foveal cones of red-green dichromats

Abstract

The intensity of a monochromatic light required just to detect 30 Hz flicker as the point of entry of the light was changed in 0.5 mm steps across the eye's entrance pupil and measured throughout the spectrum on 4 protanopes and 5 deuteranopes. In general the directional sensitivity of the foveal cone of these dichromats is minimal in the same part of the spectrum that the spectral sensitivity is maximum. Since the action spectrum of only a single class of cones was evaluated by the procedure, it permits a quantitative comparison of two alternative models for directional sensitivity, one derived from the concept of self-screening, the other from waveguiding. The overall results do not exclude either but are slightly better described by the former than by the latter.