Are octopuses really colourblind?

Octopuses and their cephalopod cousins are famous for their ability to change colour and 
hide from predators and attract mates – but they can’t see colour, at least the way we see it. So why would a cephalopod bother dressing in bright hues if potential suitors can’t see them?

Earlier this year, we reported on a pair of researchers at the University of California, Berkeley, and Harvard University who found the unique pupil shape of cephalopods allows light to enter their eyes from many directions, which could help the animals interpret colour.

Cephalopods have evolved wide pupils, which increase chromatic aberration – the fuzzy fringe of colour you see around objects when your vision is out of focus.

By changing the “depth” of their eyeball, cephalopods can bring specific wavelengths of colour to focus on their retina. This allows the animals to change the amount of chromatic blur they’re seeing to determine different colours, depending on whether or not they’re focused on the retina.

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