How they see
How does an octopus see the world?
Colour-blind, yet sees polarized light
Here is one of biology's best riddles: the octopus, a master of colour-changing camouflage, is almost certainly colour-blind. With a single kind of photoreceptor, it should in theory see the world in greyscale, and yet it blends flawlessly into coloured coral. Its trick is to read the polarisation of light, a hidden layer of the visual world we cannot access.
See through their eyes
Human ≈ 60 cpd (20/10)
How sharp is an octopus's vision?
Its eyes resolve about 6 cycles per degree (20/100), while a human reaches around 60 cpd (20/10). Its field of view spans about 320°.
How does an octopus see a human?
Its eyes resolve about 6 cycles per degree against your 60, so a face has to be roughly 10 times closer for it to pick out the detail you do. Your outline and your movement read clearly; your expression does not.
Colour comparison
How each colour shifts when seen through this animal's eyes, using the same colour model as the app. Tones a screen can't emit (such as ultraviolet) are shown as an approximation.
What colours can an octopus see?
Colour-blind in the classic sense, but exquisitely sensitive to polarized light and to brightness/contrast. (Some evidence they exploit chromatic blur to infer colour.)
Photoreceptors
Monochromat (single photoreceptor) + polarization sensitivity
Cone peak sensitivities
- Rhodopsin475 nm
How does an octopus see in the dark?
Excellent low-light contrast vision.
How does an octopus's vision compare to a human's?
An octopus sees around 20/100 to your 20/20 and, in the ordinary sense, no colour at all. It does, however, detect the polarisation of light, a whole channel of information your eyes simply throw away.
What is special about an octopus's vision?
- Sees polarized light
- Skin may sense light too
- Horizontal pupil keeps the horizon in focus
What the research shows
The single-receptor verdict rests on the octopus's visual pigment: one rhodopsin peaking near 475–480 nm, with no second photopigment to set against it, which by the usual definition leaves no basis for colour vision; the page lists 475 nm. Polarization sensitivity, by contrast, has a clear anatomical basis in the ordered microvilli of its rhabdomeric photoreceptors, which respond to the angle of polarised light and help against transparent prey and camouflage. Light-sensitive opsins have also been reported in the skin. The colour question is not fully closed. Stubbs & Stubbs (2016) proposed that an off-axis pupil combined with strong chromatic aberration could let a colour-blind cephalopod recover spectral information through focus, at a cost in sharpness. The idea is contested, and the site follows the conservative reading: a monochromat with polarization vision.
Most other numbers are estimates. Acuity for this camera-type eye is put at roughly 5–10 cpd, lower still if the chromatic-blur idea is right, and the simulation uses 6 cpd. Flicker fusion near 70 Hz is likewise estimated. The horizontal slit pupil is kept level by the statocysts, the animal's balance organs, whatever the body is doing. The key limit is simple: a phone camera does not capture polarization and a screen cannot display it, so a grayscale frame shows only the channel an octopus shares with a colour-blind human, not the one it has in addition.
Guides: Are animals colour blind? · Which animal has the best eyesight? · All guides
Scientific sources
- Marshall & Messenger (1996)
- Stubbs & Stubbs (2016)
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