Mechanisms of chromatic rod vision in scotopic illumination.

After viewing a coloured patch for 30 sec, successive contrast colours were triggered by stimulating either rods or cones. The conditions were arranged so that the rod and cone stimuli matched both with respect to chromaticness and brightness in a chromatically neutral state of adaptation. The results showed that the contrast colours triggered by rods were strikingly similar to those triggered by cones. Yet, the scotopic contrast colours, as compared with the photopic ones, were generally found to be somewhat displaced toward blue. This displacement was attributed to the difference in test conditions. Thus, it was suggested that, although rods may excite all the different types of spectrally opponent cells, they generally tend to prefer the short-wave cells. Moreover, it was concluded that the scotopic successive contrast colours are triggered by rod signals feeding into the primary rod pathway and therefore must originate centrally to the receptor level.