Rod and cone contributions to peripheral colour vision

The changes in chromaticities were measured, in a dark-adapted state, when monochromatic lights were moved from the fovea to 2.5° and 7.5° temporally. In order to analyze the contributions of the rod and cone mechanisms to these changes, the chromaticities were measured during dark adaptation following high light adaptation. For several min during the cone-plateau period, the colourmixture functions remained invariant and the outlines of the test field appeared distinct and clearcut. Just prior to the cone-rod break of the dark-adaptation curve, however, the chromaticities generally started to change and the shape of the test field became somewhat blurred. The evidence is judged to indicate that the chromaticities measured during the period of invariance are due to pure cone activity, while the shift in chromaticities measured during the further stay in the dark is due to the effect of rod intrusion.