Obligatory Oatmeal comic about the Mantis Shrimp:
The Oatmeal claims that, "the mantis shrimp sees a thermonuclear bomb of light and beauty." This piece contradicts that claim:
"Mantis shrimp have twelve photoreceptor classes. Humans have three. We derive a spectrum of colors through comparisons between our three classes; this is called the opponent process or opponency. Mantis shrimp do not do this. They collapse the spectrum into just twelve colors."
It's more like a 12 color lookup table.
> Every kind of red stimulates the bottom receptor of row 3. All shades of violet stimulate the top receptor on row 1
That's based on an experiment where they were trained to attack colored lights for a reward.
The comic also says they have 16 color receptors, but the other 4 (2 in the midband and 2 in the hemispheres), as far as anyone knows, aren't involved in color vision.
If so, I think that's still kind of a cool thing to think about.
It's an interesting question. If you want to read more, the two researchers quoted in the book that I was summarizing are Justin Marshal and Mike Land. Each has a handful of papers that are cited in the bibliography.
Instead of co-located and connected cones for different colors, they drag their eyes across a scene, so the comparison can happen across time instead, like a push broom sensor.
Also of interest, mantis shrimp are edible and quite delicious.