Implication of the Yellow Pigment in Dichoptic Colour Mixing

Working with colours generated from the three primaries, we found earlier that blue made it difficult to obtain dichoptic mixtures, producing chromatostereopsis and alternation effects which disappeared with increasing eccentricity (1 deg 3 min) or decreasing intensity of the blue component. The unanswered question was: is it true that mixtures with a strong blue component can never be obtained centrally as some authors claim? Therefore, we returned to this subject, using the same methodology and analysing the role that the yellow pigment (YP) would play.

First, the samples that previously produced the aforementioned effects were tested, confirming that chromatostereopsis stopped before the alternation. Immediately after that, identical samples were observed through low-density yellow filters that were superposed until both effects ceased. Since the density of the YP of the four participating observers had been previously measured, it was possible to calculate the necessary increase for each one of them, observing that the increment became smaller as the mixtures were displaced towards longer wavelengths.

This behaviour indicates a possible function of YP: the attenuation of the blue cone signal to make it compatible with signal from the red and green cones. As the YP varies among observers, this might be the reason why some sources mention that these mixtures can be obtained. If this hypothesis is accepted, this should not be interpreted as a variation in the number of blue receptors through the macula, a variation not necessarily observed in physiology.