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| © Elaine Molina Stephens, 2024. |
“But do cats eat bats, I wonder?” And here Alice began to get rather sleepy, and went on saying to herself, in a dreamy sort of way, “Do cats eat bats? Do cats eat bats?” and sometimes “Do bats eat cats?” for, you see, as she couldn’t answer either question, it didn’t much matter which way she put it.[…] did you ever eat a bat?
—Alice in Alice’s Adventures in Wonderland, 1865
Imagine you’re an animal. That shouldn’t be hard since you are an animal. So to be more accurate, imagine you’re another type of animal—a cat.
Back in 1974 philosopher Thomas Nagel wrote his well-known essay, “What is It Like to Be a Bat?”[1] Philosophers and scientists have had many interesting discussions over it ever since. In his argument against reductionism, he insisted that it’s impossible for us to know what it’s like to experience the world as a bat, since their sense of echolocation is so alien to us. He has a point, but while we may never know what a bat’s view of the world looks like after its brain processes the data from its senses, we have learned a lot about echolocation and how a bat’s senses work, thus we’ve gained insight into what their world might be like.
We can’t yet know what it’s like to be another animal, just as we can’t know what it’s like to be another person, but I’d like to go over a few things we’ve discovered, mostly since Nagel wrote his essay. This won’t deal with qualia—the subjective, conscious experience—but I think it’s a step forward in understanding what these creatures experience. It may not be long before we can accomplish this better with immersive virtual reality. Nagel used bats as an example, but he intended his argument to apply to all animals, so I’d like to look at a few others that we’re a bit more familiar with.
Dogs and cats can’t see nearly as well as us. Both are red-green color blind, so to them the world is in washed-out shades of yellow and violet, although some experts think cats only see in violets and grays. Either way, this means green pretty much looks yellowish white to them and red looks gray to yellowish gray. If you throw a red ball into grass, your dog will have to search for it mostly by its shape. So get your dog a blue ball. In addition, as their eyes are three feet (1 m) or less from the ground, objects like long grass can block much of their view.
One recent study by researchers in Hungary and Mexico suggests that dogs don’t really notice the differences in people’s faces, since unlike us, they don’t have a specific area in their brains for processing faces. They mainly recognize you by your voice, smell, or movements, probably with a bit of help by your clothing or other distinguishing features.
Dogs and cats have a wider field of view than we do, but with dogs there’s less overlap of their eyes, so less of their view is three-dimensional. On the other hand, dogs and cats have a visual streak instead of a fovea, so their peripheral vision is better since the streak puts a greater length of the horizon in focus, whereas our fovea is just a spot.
They also see less contrast than we do. Because they have more rod—receptors that detect black and white, providing night vision—than us, everything appears lighter and they’re better at detecting motion. They’re particularly good at detecting objects moving at certain speeds, but slow moving objects may look stationary to them and they’re not as good as us at seeing motion in the bright light of day, although dogs can see a little better during the day than cats.
But other vertebrates, such as fish and reptiles, may have color vision even better than ours, with four color receptors. Birds and turtles can see more shades of red and ultraviolet than us because their red receptors peak closer to infrared and they have an ultraviolet receptor. This would mean birds, fish, and reptiles have day vision; dogs, cats and most mammals have night vision; while we fall in the middle.[2]
So throwing a ball that is red for your dog to chase will increase the chance he or she will lose it, but you can use it to play fetch with a turtle, especially since turtles are attracted to red, but that probably won’t be a very exciting game.
Both dogs and turtles see much better than us at night, but it’s essentially in black and white. They can also see ultraviolet light to some degree, which helps them with night vision. Dogs, cats, owls, deer, raccoons, and some other mammals have a reflective layer of tissue behind their retinas to help them see better in the dark. Photons that pass by their receptors are reflected back through the retina giving them a second chance at being received. This is why their eyes glow in the dark when you shine a light on them.
On the down side, because the layer scatters light, these animals’ visual acuity is much less than ours. Cats don’t see well close up or far away—it’s more in the midrange, although outdoor cats can see well slightly farther away, while indoor cats can see better a bit closer. This doesn’t mean everything is fuzzy, it’s likely if they look at a brick wall they’ll clearly see the wall—they just won’t see the bricks. What they see will lack detail.
It’s thought that cats and dogs can’t adjust the focus of their eyes to different distances as well as we can, and that ten inches (25 cm) might be the maximum for cats and twice that for dogs, so only things in a narrow distance would be in focus. Cats can’t focus on anything that’s less than a foot (30 cm) in front of them, so they rely on their whiskers to sense those things. Of course, many people have a similar problem and rely on their reading glasses.
If you have 20/20 vision, what you can see at between 50 and 100 feet (15-30 m) is about as focused as what most dogs see at 20 feet (6 m). Certain breeds—such as Labradors, Australian Shepherds, and Alaskan Malamutes—were bred for better eyesight and can see almost as well as us, while others—Toy Poodles, Collies, and Rottweilers—are nearsighted.
For cats, what they see at 20 feet (6 m) would be about as clear as what we see at between 100 and 200 feet (30 to 60 m). In other words, cats would be considered legally blind and dogs are close. And both cats and dogs can’t see anything you put under their nose, since their nose is in the way. We don’t have that problem.
I find it interesting that the seeing-eye dogs used to assist blind people are not that great at seeing. Fortunately their other senses are much keener than ours.
Why Cats and Dogs are Color Blind
Vision originally evolved in the ocean, which is probably why we see the spectrum of light that we do. Electromagnet radiation just above ultraviolet and below red is absorbed by water, so it’s likely vision evolved to make use of what was left. The common ancestor of reptiles, birds, mammals, and dinosaurs probably had good color vision, as many fish do.
As dinosaurs evolved to be large successful predators, they came to dominate the daylight hours. Their cousins, the reptile-like proto-mammals, found they could better avoid becoming dinosaur kibble by foraging at night. Throughout the reign of the dinosaurs, our ancient ancestors were nocturnal, so their vision evolved to better see at night by increasing their rods and losing two cones—red and ultraviolet—reducing them to the two remaining cones that almost all mammals still have. Birds and reptiles still have three or four of them.
Millions of years ago dinosaurs were the monsters that drove mammals to forage at night. Now it’s happening again with many animals being forced to forage at night, only this time we’re the monsters driving them to it.
When all the dinosaurs were wiped out, except for those who would evolve into birds, mammals returned to living in the daylight. Somewhere along the line primates regained their red receptor, restoring the tri-color vision that apes (including us) and Old World monkeys have today, but which New World monkeys don’t, except for Howler monkeys who regained it on their own. These are the only animals in the world who see colors the way we do. And this is why most mammals, including dogs and cats, have poor color vision.
Mammals and their ancestors went from day to night vision, and have returned to mostly day vision. Humans have progressed further on this path than dogs and cats. Similarly, the reptilian ancestors of crocodiles, alligators, and turtles moved from water to living on land, but later returned to water. While on land their eyes adjusted to seeing through air, which is very different from seeing through water, mainly because of refraction, or the bending of light when it hits water. Turtles have adjusted, so they can see fine in air and water, but crocodiles haven’t. They still have trouble seeing underwater, just as we do.
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[1] Thomas Nagel, “What is It Like to Be a Bat?”, The Philosophical Review, vol. 83, no. 4, October 1974, pp. 435-450, https://www.jstor.org/stable/2183914.
[2] Richard Dawkins, The Ancestor’s Tale: A Pilgrimage to the Dawn of Life, Boston, MA: Houghton Mifflin, 2004.
And Evan Thompson, “Colour Vision, Evolution, and Perceptual Content”, Synthese, no. 104, 1995, pp. 1-32, http://individual.utoronto.ca/evant/ColourSynthese95.pdf.
And University of Texas at Austin, "New study shows effects of prehistoric nocturnal life on mammalian vision", ScienceDaily, October 31, 2012, http://www.sciencedaily.com/releases/2012/10/121031161025.htm, citing M.I. Hall, J.M. Kamilar, and E.C. Kirk, "Eye shape and the nocturnal bottleneck of mammals", Proceedings of the Royal Society B: Biological Sciences, 2012, https://royalsocietypublishing.org/doi/10.1098/rspb.2012.2258, https://doi.org/10.1098/rspb.2012.2258.
Also Veronique Greenwood, “Eye of the Beholder”, New Scientist, April 18, 2015, pp. 40-43, and as “Eye of the beholder: How colour vision made us human”, April 16, 2015, https://www.newscientist.com/article/mg22630170-400-eye-of-the-beholder-how-colour-vision-made-us-human.
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