Scientists see a colorful world through the eyes of a cephalopod.
Most people have 3 types of cone cells in their eyes that are sensitive to red, green, and blue light. But cephalopods — a group that includes octopuses, squid, and cuttlefish — have only 1 type of light receptor in their eyes, which has led scientists to believe that they are incapable of color vision.
At the same time, cephalopods use a rainbow of colors in their everyday lives. They are masterful camouflage artists, sometimes referred to as the “chameleons of the sea.” Some also use colorful displays to impress potential mates, startle predators, and communicate with one another.
“That was a big paradox,” Alexander Stubbs, a biologist from University of California, Berkeley, tells The Science Explorer. “How do cephalopods change color accurately and display to each other, or why would they display to each other in color, if they don’t have the normal conception of color vision?”
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Stubbs suspected cephalopods might employ some alternate method of detecting colors, perhaps one that took advantage of their bizarre U-shaped, W-shaped, and dumbbell-shaped pupils. In contrast to our own round pupils that contract to pinholes to give us sharp vision, cephalopod pupils allow light to enter the eye from many directions, creating blurred images — an effect called chromatic aberration.
He teamed up with his father, astrophysicist Christopher Stubbs from Harvard University, to explore how cephalopod eyes might sense color, through computer models designed to mimic their visual system.
While photographers try their best to minimize the colorful fringes around objects that chromatic aberration creates, cephalopods actually appear to use this effect to separate light into its component colors, or wavelengths. Then, as Christopher explains, they can move their retinas back and forth to allow different wavelengths to come into focus, one at a time, allowing them to determine the “spectral content in the scene”.
As Stubbs and Stubbs conclude in their paper, published in the Proceedings of the National Academy of Sciences, cephalopod eyes are well equipped to see in color through this elegant mechanism.
But even if they are able to see colors, exactly what blue, gold, or purple looks like to cephalopods remains unknown. Alexander thinks what they see is likely very different from our own perception of color.
“It’s not something that I would say definitively, but it would surprise me greatly if, through independent evolution of color vision and a completely different mechanism, that things would appear at all the same,” he says.
Christopher agrees, pointing out: “Philosophers would even ask whether the three people on this phone call perceive color the same way.”
Watch an octopus and cuttlefish change colors to camouflage themselves and display to other members of their species in this video: