Fig 5. Same as Fig 2, but amplitude sensitivities for protanopic observers ML (left panel) and MM (right panel) provided by AS, originally shown in Figures 3 and 4 in Stockman et al. [13].

Stockman et al. used a centrally-fixated, 4° diameter, 610-nm target superimposed on 9° diameter 540-nm background. The ratio of the target and background radiances was fixed to produce a maximum M-cone contrast of 13%. The error bars are ±1 standard error of the mean. This combination of background and target radiances helped to eliminate rod intrusion at low retinal illuminances (as confirmed in their bleaching control experiments).