Abstract
The relative number of L and M cones in the human fovea is estimated by combining two sets of measurements. Increment thresholds for red and green tests are measured on backgrounds of varying wavelength. The wavelength at which the thresholds are raised by equal amounts over their dark adapted levels is deemed to be that for which individual L and M cones are equally sensitive (iso-lambda). The statistics of the color appearance of small, brief, near threshold lights are obtained for the same observers. The relative frequency with which stimuli at iso-lambda are called red and green defines the ratio of numbers of L to M cones in the fovea.
Supported by NIH grant EY06388.