Color coding and its interaction with spatiotemporal processing in the retina
We use the theory of early visual processing proposed in ref.  to deduce the color encoding strategies of the retina. The calculated retinal transfer functions display a nontrivial coupling between color and spatiotemporal processing even when the autocorrelator of natural scenes has no coupling between the chro¬matic and the space-time dimensions. This coupling in the transfer function is fundamentally due to photoreceptor noise, and where red and green cone activities are highly correlated, as they are in humans and monkeys, it leads to the spatio¬temporal-chromatic opponent ganglion cells found in primates. Ignoring the blue cones, we find two types of ganglion cells whose receptive field organization is either red center with a green surround or green center with a red surround, as found by Derrington et al.  in monkeys. On the other hand, when the correlation between the red and green cone outputs is small, as is the case in shallow fresh water fish, we arrive at the "double opponency" cells observed in goldfish. We also argue that adding blue cones (which are rare) leads to a third type of cell with R + G — B opponency.