Do rods influence the hue of foveal stimuli?

To understand the generality and mechanisms of previously reported rod hue biases, we examined whether they are present for small foveal stimuli by comparing the wavelengths of the three spectral unique hues under dark-adapted and flash-bleached conditions. Rod green bias (shift of unique yellow) and rod blue bias (shift of unique green) were found for some observers with 1 degrees -diameter foveal stimuli, the size most likely to stimulate rods. Smaller stimuli (0.2 degrees and 0.6 degrees diameter), which were least likely to stimulate rods, produced no large or consistent differences between dark-adapted and bleached conditions. This suggests that rod hue biases result from the local stimulation of rods by light, not from remote suppression by dark-adapted, unstimulated rods, and not from bleaching light artifacts.