
Shark and ray vision comes into focus - dnetesn
https://phys.org/news/2020-01-shark-ray-vision-focus.html
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mhandley
_" Sharks and rays do contain both rod and cone photoreceptors; however rays
possess two cone opsin genes whereas sharks have only one cone. Sharks
therefore were found to have lost the ability to see colors."_

Surely if you have both rods and one type of cone, you do still have some
degree of colour vision, from the difference between the rod and cone response
curves? Either the rods and cones both respond (one end of a colour spectrum),
or just the rods respond (other end of the spectrum), and colours in between
can be distinguished to some degree by the relative differences as the cone
response progressively drops off.

~~~
awb
> Sharks therefore were found to have lost the ability to see colors.

I've heard that bright color bathing suits might intrigue sharks as it could
resemble some type of colorful fish. Is this just an urban myth?

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Footkerchief
The paper expands on "disadvantages of color vision":

[https://academic.oup.com/mbe/advance-
article/doi/10.1093/mol...](https://academic.oup.com/mbe/advance-
article/doi/10.1093/molbev/msz269/5625936)

> Color vision requires opponent neural mechanisms that compare the output of
> different spectral photoreceptor types. Inhibitory interactions between
> photoreceptor channels can decrease the signal-to-noise ratio and,
> therefore, may degrade the ability to detect subtle differences in image
> contrast (Kelber and Roth 2006); in dim light, a monochromatic visual system
> may be capable of discriminating a greater number of distinct reflectance
> spectra than a di- or trichromatic one, purely based on intensity
> differences (Vorobyev 1997). Color vision also degrades spatial acuity,
> especially when the spectral peaks of the photoreceptor channels are widely
> separated, because the signals from different cones types will reflect both
> spectral and intensity differences in the image (Roorda et al. 2001). For
> this reason, many animals rely predominantly on a single spectral channel to
> convey high-resolution achromatic spatial information (Lind and Kelber
> 2011), but of course any other spectral cone types are then taking up
> valuable retinal “real estate” that could otherwise be used to improve
> resolution in bright light (i.e., more receptors per degree of visual angle)
> and/or reduce noise in dim light (i.e., through neural summation). Due to
> absorption, reflection, and scattering by the water itself and any dissolved
> or suspended substances, most aquatic habitats are characterized by low
> visual contrast. Moreover, many sharks are active both night and day and
> must therefore operate under a wide range of light intensities. It is likely
> therefore that sharks are often operating close to the threshold of their
> visual capabilities where the disadvantages of color vision circuitry might
> be detrimental to survival.

~~~
Gravityloss
IIRC color blind people were recruited to do reconnaissance photo analysis
during the war in the UK.

