Reeves A
J Opt Soc Am A. 1987 Mar;4(3):525-9. doi: 10.1364/josaa.4.000525.
Stiles's middle-wave color mechanism Pi-4 is field additive for mixtures of 410-, 480-, 530-, 622-, and 670-nm adaptation fields, when studied with a 1-deg, 200-msec, 500-nm foveal test flash at 10 times absolute threshold.