Here’s a tip for the novice pet owner: don’t buy your pooch a red ball and then throw it in a green field. Chances are, neither of you will have a lot of fun.
The reason for that, it transpires, is that dogs are colour blind.
A team of researchers at the Department of Veterinary Medicine at the University of Bari in Italy made this discovery after conducting a series of tests on dogs to try to determine their visual capacity.
The old saw that dogs see only in black and white was found to be only partially true as far back as 1989, when a study identified two types of cones – cells that detect colour – in dog retinas.
A 1995 analysis of vision studies in dogs, published in the Journal of the American Veterinary Medical Association in 1995, concluded that the two types of cones – sensitive to wavelengths around 450 nanometres and one at about 550 nanometres respectively – meant dogs probably had dichromatic vision.
They were likely to be able to see some blue tones, with the 450nm cones, and somewhere in the “greenish-yellow, yellow, and red range” with the other one. The range in the middle, the researchers suggested, was probably perceived as white or grey.
In the latest research, Marcello Siniscalchi and colleagues demonstrate that visual acuity in the green-to-red range doesn’t distinguish between the two colours.
To make their finding, the researchers subjected dogs to a canine version of the classic Ishihara’s test, used by optometrists the world over to test human for colour blindness.
In the human version, the test comprises a series of patterns made up of variously sizes dots or bubbles. A number or symbol made of red dots lurks within a matrix of green ones (or vice versa). People with red-green colour blindness are unable to distinguish the signal from the noise.
Siniscalchi’s team refined the test for canine sensibilities, and used animated cat silhouettes of various colours superimposed on various backgrounds. They found that if the cat was red and the background green – or vice versa – the dogs did not react.
The researchers write that their work has confirmed that dogs have dichromatic vision. Adapting the test, they add, potentially provides a tool for testing colour vision among other members of the animal kingdom.
Andrew Masterson is a former editor of Cosmos.
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