Abstract
We have previously shown that rod signals influence the balance of both red-green and blue-yellow opponent hue dimensions, but in a pattern that is inconsistent with simple additive combinations of rod and cone signals in opponent-color models (e.g., rods can produce both a red bias and a green bias). The shifts are instead consistent with non-linear models in which rod influence requires non-zero cone signals. Here we challenge this model with new data on the time-course of the rod hue biases. The rod green bias (typically 5–15 nm) and rod blue bias (typically 20–30 nm) observed near unique yellow and unique green, respectively, were not systematically affected by test stimulus duration. Near unique blue, rods exerted a green bias (typically 5–10 nm), for test stimuli less than 50 ms, and a red bias (typically 5–15 nm) for longer test stimulus durations. The rod red bias reached asymptote for all observers within 50 ms. We find that the model accommodates well the group-averaged results but that there are important individual differences among the observers that pose challenges to be addressed in future.