Interchangeable backgrounds for cone afterimages.

Observations of afterimages indicate that red and green cone sensitivities can be modified jndependentiy by bieaehing. providing a way to estimate their sensitivities in the normal eye. The fovea1 afterimage of a red and green bipartite held is allowed to fade against a steady red background. A change of background color from red to green generally revives a bipartite afterimage. If two conditions are met. however, a uniform. borderless afterimage is revived instead. These conditions are: ii) the radiances of the bleaching hemitieids must be equated for one of two spectrally selective mechanisms and (2) the substituted backgrounds must be equated for the other mechanism. Derived spectral sensitivities of the two mechanisms in the red-green range agree with the spectral sensitivities of protanopes and deuteranopes obtained from visual matches. and also with those derived from temporary artificial protanopia and deuteranopia in normals. The mechanisms are :herefore identified with the normal redand green-sensitive cones. and it is concluded that the sensitivity losses that generated these afterimages were applied independently to separate signals orginating from the two cone types.