Abstract

The frequency of the seeing curve and absolute thresholds including their relation to area show that two to four quantum absorptions in a group of one to three red cones, one to three green cones, or in a group of a variable number of rods suffices for vision. The proportionality of absolute threshold and chromatic threshold with a square root of stimulus area indicates that both rely on a twofold quantum coincidence mechanism. Luminance signals from two or more singly hit red and green cones and color signals from multifold hit red and green cones can be discriminated. Achromatic intervals and frequencies for specific color names around threshold level indicate that these signals are generated in ommatidia consisting of two red cones, two or three green cones, and one blue cone. The scotopic receptive unit at 12° nasal from the fovea then has about sixty submits in which two and more quantum absorptions in rods produce white signals. The scotopic achromatic signals originate from two or more submits which are each excited by one or more quanta. Each submit may contain a single cone with about forty satellite rods.

© 1987 Optical Society of America