Foveal increment thresholds in protan observers

The colour mechanism sensitivities of three protanomals and three protanopes have been measured at various spectral points, in an attempt to describe some anomalies of increment threshold data in terms of interaction effects. The π₂, secondary maximum is greatly reduced and the π₁ inflexion apparently increased in both protanomals and protanopes. π₅ has a sensitivity similar to that of π₄, and π₅′ has a spectral sensitivity different to that of π₅ in prolanomaly; π₅ and π₅′ are lost in protanopia. The primary modes of the auxiliary blue mechanisms π₁ and π₂ are independent of π₄ and π₅, while the secondary mode of π₂, seems to depend on the difference in gradient of π₄ and π₅. π₄′ and π₅′ sensitivities are affected by changes in π₄ and π₅ and also by some factor which manifests when π₄ and π₅, are altered. This factor is not related to the spectral sensitivities of the other mechanisms.