Wave-length discrimination at the foveal chromatic threshold.

1. Wave-length discrimination has been measured at the chromatic threshold to test the assumption that when a monochromatic stimulus is reduced to its chromatic threshold, the activity of a single cone mechanism may be isolated.2. It has been shown that, at the chromatic threshold, all wave-lengths between 559 and at least 665 mmu are significantly confused. Similar ranges of confusion extend from 457 to 570 mmu and from 485 to at least 419 mmu.3. These results have been shown to be consistent with previous measures of the spectral sensitivities of the cone pigments. They support the view that the hue of a monochromatic stimulus at its chromatic threshold may be dependent on light absorbed by only one cone pigment.