Contrary to popular belief, cats and dogs can take in a lot of visual information while they watch their favourite television shows, and this doesn't have to be restricted just to Animal Planet.
Dogs can see some colours. They see colours in the blue spectrum pretty well but are red-green colour blind, having only two types of cone cells at the back of their eye, compared with us humans who possess three types of cone. We also have these colour-reading cones at 10 times the density of our furry companions, a big advantage to enjoying the full spectrum of colourful shows on the box.
Cats see a little fuller range of colour in the blue, green and yellow spectrums when compared with canines (one of the many reasons they think of themselves as superior, I'm sure), but see very little reds.
Our pets have limited ability (about one-sixth of our own) to see the fine detail of Shortland Street's dramatic screenplay. They lack a fovea, which is an area of the retina consisting of extra highly concentrated cones that all people have. This leaves them with acuity of only 20/75 vision, meaning they will see an object from 20 metres away as well as you or I would see the same object standing 75 metres away. John Campbell will be looking a little blurry to them even when they're lounging on your favourite La-Z-Boy, just a few metres back from the 50-inch plasma.
Dogs and cats are, however, much more adept at detecting movement and they focus well on the edges and outlines of the animals or people they're watching on the screen (or in real life). This is especially important to them considering so much of our pets' social interaction relies on postural movements (canines even more so than felines).
Certain breeds of dogs, such as labradors, do have better eyesight than others - handy for locating those ducks on National Geographic.
Instead of our fine-detail fovea, all cats and dogs have a tapetum, which is a reflective area of the eye that boosts the brightness of light hitting the retina. They also have more rods than we do (instead of our extra cones) at the rear of their eye and these two features allow much better night vision. Apart from the cool "glow in the dark" eye effect this creates, this also provides a very useful night-vision advantage, coping with around four to six times less light than our own eye.
Dogs can't judge distances as well as we do, due to a more lateral position of their eyes, but they have better peripheral vision to catch those pesky cats sneaking up on them to steal their chair.
Cats, on the other hand, have even better depth judgment in the nearsighted range than our own (a re-run of Jaws 3D could get interesting for them), dropping off quickly at further distances away.
Cats actually see similar definition as humans and have even better night vision than their canine friends, aided by their elliptical, faster-adjusting pupil.
Cats process visual information much faster than all the rest of us (superiority complex again) and to their eyes our older, standard 50Hz television sets will usually appear to be projecting a mind-numbing, garbled flicker (they possibly are). Interestingly, studies have shown that this processing speed ranges markedly among individuals, and that some "slower" thinking cats (like my Burmese, Yoda) will see these 50Hz images just fine. Most cats, however, would much prefer to watch a set with a 100Hz picture frame rate, in itself a valid reason for all animal lovers to buy a new LCD screen immediately.
I guess to help keep all our cherished pets happy this winter and enjoying their viewing you should turn the brightness right down and pick out shows with lots of fast-moving action scenes where everyone's wearing lots of blue or stripes. I'm thinking a prison show, the Smurfs or some underwater James Bond scenes would be ideal.
Dr Alex Melrose, BVSc, MRCVS, is an Auckland veterinarian.
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