Mechanisms of rod-cone interaction: evidence from congenital stationary nightblindness.

The dark-adapted rod system can elevate cone-mediated thresholds for flicker detection as well as thresholds for the detection of hue. We examined these two types of rod-cone interactions in two individuals with congenital stationary nightblindness (CSNB), a retinal disorder in which rod outer segment function is intact, but in which a defect occurs in the transmission of rod signals within the retina. The two types of rod-cone interaction were differentially affected by the retinal pathology; the rod-cone flicker interaction was normal, but the rod-cone hue interaction was absent. These results provide evidence that, despite similarities in the adaptational properties of these two types of rod-cone interaction, they are mediated by different visual mechanisms.