The question of how octopuses can match their surroundings while not being able to see colours is one hell of a puzzle. Christopher Stubbs may finally have found the answer: chromatic aberration.
Maybe octopuses do see colour – not from light hitting special retinal “photoreceptors” but thanks to chromatic aberration, where different colours of light focus at different distances behind a lens.
Eyes of cephalopods are quite unlike anything seen on land: U- and W-shaped pupils backed by a lens that moves back and forth, like a camera, rather than fattening or thinning like ours. But they also have only one photoreceptor, unlike our red, green and blue ones.
Stubbs idea is the following: by adjusting the focal point of their eyes, like a photographer adjusts a lens, cephalopods might be able to detect different wavelengths – or colours – of light. This is called chromatic aberration.
To test his idea, Stubbs created a computer model of how the animals’ eyes work and see if chromatic aberration was possible.
He found not only could a shifting lens do the trick, but the cephalopods’ quirky pupils only served to maximise the effect. As Stubbs says, these creatures might exploit a ubiquitous source of image degradation in animal eyes, turning a bug into a feature.
The unusual pupils of cephalopods (from the top, a cuttlefish, squid and octopus) allow light into the eye from many directions, which spreads out the colors and [certainly] allows the creatures to determine color, even though they are technically colorblind.
As the lens moved forwards and backwards, the different wavelengths focusing on the retina at different times built up a colour picture.
It is not a proof, but the idea is definitely worth investigating !
The latest fascinating cephalopod insights come to us from a
father/son team of researchers at the University of California, Berkeley
and Harvard University, who’ve learned that weirdly-shaped pupils may
allow cephalopods to distinguish colors differently from any other
animals we know of. The discovery is published this week in the Proceedings of the National Academies of Sciences.
Boring animals like humans and birds see color using a combination of
light-receptive cone cells, each of which contains pigments that are
sensitive to a different part of the visual spectrum. It’s only by
combining information from different cone cells that colors can be
properly distinguished. Hence, when a person lacks a particular type of
cone, he’s considered colorblind.
Cephalopods only have a single type of light receptor, which means
they should not be able to distinguish color at all. And yet, many
octopuses, squids and cuttlefish have color-changing skin that’s used
for elaborate camouflage ruses and courtship rituals. Clearly, these
colorblind animals have become masters of color manipulation. How? …
#DidYouKnow - The narrower the pupil in relation to the horizon, the greater accuracy of depth perception in peripheral vision? Pair that with the fact that the octopuses optical nerve fibers are behind retina and you get absolutely no blind spot which means an octopus can see everything that is going on in their environment. Pretty cool huh nation?! 📸: Gustavo Maqueda
