by Ziya Tong
Goldfish do indeed have remarkable eyesight. They not only have red, green, and blue cones for colour vision, as we do, but they have an additional fourth receptor, for UV light, meaning an entirely other way of seeing is open to them that is closed to us. When you stop to think about it, it’s perhaps not surprising that animals have good eyesight: we expect that they would in order to survive. But what is surprising is the kind of information that some animals are able to perceive.
Archerfish, for instance, can distinguish between individual human faces. The fish have a rather unique skill for an aquatic species: like biological water pistols, they spit out jets of water to shoot down aerial prey. The fish can target an insect above the water and strike accurately at even sixty centimetres away. This special ability gave researchers at the University of Oxford and the University of Queensland an idea: they wanted to see if the fish’s accuracy and keen eyesight could be used in another way. So they gave the fish paired images of human faces along with a food reward and trained them to use their jets to strike at the image of one particular human face on a computer screen.
Given how similar human faces look—with the same basic structure of eyes, nose, and mouth—even we sometimes have difficulty discriminating within our own species. But for a fish, especially one with such a small brain, and one that did not evolve human facial recognition abilities, the results were stunning. Presented with a sequence of forty-four new faces paired each time with another face they had been trained to remember, the archerfish demonstrated excellent visual recognition, selecting the correct face during the trials with 86 percent accuracy. *1 If that doesn’t seem impressive, ask yourself if you could pick out the face of one archerfish from a school of forty-four.
Common pigeons are also known to have highly sophisticated vision. They can distinguish each letter of the alphabet, recognize dozens of words, tell the difference between paintings by Monet and Picasso, and even recall up to 1,800 individual images. Researchers, aware of pigeons’ excellent discriminative powers, wanted to see how they would fare in a highly complex task: discerning the difference between malignant and benign growths in breast biopsies. Malignant tumours that turn into cancer are often signalled by micro-calcifications in the breast tissue and are distributed in a particular way. For radiologists and pathologists, it can take years to acquire the skills to distinguish between malignant and benign masses. The pigeons weren’t given years. They were trained for only thirty-four days using a touch screen attached to a food pellet dispenser.
During training, the birds were shown images on a screen and were rewarded when they correctly tapped either a yellow bar when the biopsy was benign or a blue bar to signal that it was malignant. The pigeons were amazingly accurate, making a correct identification, even on new images, at a rate of 85 percent. When the researchers took a “flock sourcing” approach and pooled the responses of all sixteen trained birds, the accuracy rate went up even higher. Together, the pigeons gave an accurate diagnosis 99 percent of the time.
The point is not that we should replace radiologists with pigeons, but we should at least begin to question our ideas of what intelligence means. We set the bar at the default position of human intelligence, but since we can’t assume that pigeons are smarter than radiologists, clearly we have to reappraise what intelligence is.
One aspect of intelligence is our ability to interpret visual information, to make sense of and respond to the world before us. For humans, that includes the ability to perceive spatial information, to read words and decode maps, and to understand symbols. Sight is not a requirement for any of those skills, of course, but it is a sense we rely heavily upon and is an aid in navigating through our environment. And yet even without all that sophistication, a homing pigeon can do something most of us cannot: randomly dropped off hundreds of kilometres away from its loft, the bird will always—remarkably—find its way home.
Today, of course, we have GPS, but imagine if we had the inbuilt capabilities of a migrating bird or homing pigeon? We now know that fish, birds, turtles, mammals, insects, and even bacteria can detect magnetic fields. If we could do the same, how would it change the way we think? And would it make us more “intelligent”?
These are rhetorical questions, but they point to the fact that we see our world through the tiniest pinhole of perception. There are at least 8.7 million other animal species on Earth, each with its own way of perceiving. So let us take a look through some of these lenses and see how other species experience our world.
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REALITY IS LIKE AN IMAGE composed of billions of different pixels, each with its own distinct view. As primatologist Frans de Waal has noted, “This is what makes the elephant, the bat, the dolphin, the octopus, and the star-nosed mole so intriguing. They have senses that we either don’t have, or that we have in a much less developed form, making the way they relate to their environment impossible for us to fathom. They construct their own realities.”
Meaning, what we know as “reality” is only a fractional view. Our eyesight, for example, is limited to a mere 0.0035 percent of the electromagnetic spectrum. What we call “visible light” are the wavelengths within the range of 380 to 700 nanometres. Light with a wavelength of around 700 nanometres is red; at 600 it’s yellow-orange; at 500 it’s green; at 400 it’s blue-violet. The spectrum above and below that range is invisible to our eyes. But even what we do perceive as “colours” do not really exist in the outside world. They are interpreted inside our brains and are dependent on the number and type of receptor cells in our eyes that are attuned to particular wavelengths.
In a mist of sunshine and rain we see the brief biological wonder of the rainbow, the part of the arc that corresponds to the visible spectrum. On either side of it are the invisible wavelengths that we are not biologically equipped to see. As Philip Morrison writes in the foreword of Super Vision, “Go in one direction from the visible portion of the electromagnetic spectrum, and the last bit of violet fades out, giving way to ultraviolet colors, then to X-ray colors, then to ever more exotic invisible colors known as gamma rays. Go the other way and the last bit of red gives way to infrared colors, which we feel as heat instead of see as beyond-red colors. Continue in that direction and you get to the longer wavelengths that now fill the airwaves conveying radio and television programs, billions of cell-phone conversations…radar signals from air-traffic control towers and air-defence systems.”
In other words, we think of X-rays as being invisible, but all that means is they are invisible to us. That is, invisibility describes not the X-ray but our own way of seeing or not seeing. Some animals perceive light in wider ranges of the spectrum than we can; specifically, ultraviolet and infrared. Snakes like pythons, boas, and pit vipers have a specialized “pit organ” between their eyes and nostrils allowing them to see in the 750-nanometre to 1-millimetre infrared range. Even blindfolded, the snakes can accurately strike their prey. That’s because the pit organ is sensitive to radiant heat, picking up individual temperature readings which it uses to generate an image in the brain. In this way, a viper can “see” a warm-blooded mouse in the dark.
Bees also see beyond the visible spectrum. A black-eyed Susan flower, for instance, might appear to us as a bloom of yellow petals, but to a bee that can see down to the 300 nanometre range in ultraviolet,*2 it’s lit up like a landing strip. Gardens are filled with these secret bull’s eyes, invisible to us but lit up for the bees to find nectar. Golden eagles likewise see ultraviolet light—they use it to follow the fluorescing urine trails that lead to their prey *3—but they also have killer visual acuity. While we gauge good eyesight as being 20/20,*4 eagles have 20/5 vision, meaning that an object visible to you at five feet away would be visible to an eagle from twenty feet. That’s because the fovea in an eagle’s eye—the part of the eye responsible for visual acuity—is much deeper than our own, allowing it to see close up, like a telephoto lens on a camera.
An eagle’s eyes are so goo
d, it can spot a rabbit from 1.6 kilometres away. That’s like you being able to see an ant from the top of a ten-storey building, or having nosebleed seats at a stadium rock concert but still being able to clearly see the performers’ faces. Raptors also have exceptional colour vision. An eagle’s fovea is packed with cone cells, giving it incredibly vibrant resolution. While humans have about two hundred thousand cones per millimetre at the centre of the fovea, eagles have one million. That’s like seeing the world on an old TV set, in low resolution, versus seeing it in ultra-high definition.*5
Humans are also somewhat limited by the placement of our eyes in the front of our heads, which gives us a field of view that’s around 180 degrees. Eagles, whose eyes angle thirty degrees back from the midline of their faces, have a visual field that’s 340 degrees. But while we hear the term “eagle eyes” quite often, in this particular domain hammerhead sharks have eagles beat. With their wide heads, the powerful predators have full 360-degree stereo vision. Not only can they see both in front of them and behind, these animals can also simultaneously see what’s above them and below.
Even our planet’s “lowliest” creatures have abilities we are only now starting to appreciate. The humble dung beetle makes its living by rolling fresh feces into a ball two to three times its own size. Then, by manoeuvring onto its front legs like it’s doing a handstand, this hard-working insect uses its hind legs to push its prize backward away from the dung heap and the competition as quickly as it can.
But how does it know where to go? Face down, with a big ball of feces blocking its view, the dung beetle still has an uncanny sense of direction. Scientists discovered that the beetles know where they are and where they are going by mapping the skies. If you watch a dung beetle, you’ll notice it climb on top of the dung ball every so often and perform what appears to be a little dance. It has been known for some time that what they are actually doing is taking a mental snapshot, a 360-degree panorama of the sky. By comparing a mental image of the location of the sun or moon overhead to their internal map of the heavens, they are able to track their position and move continuously in a straight line.
But researchers were curious: What about moonless nights? How does the nocturnal dung beetle species get around without a bright marker in the sky? To find out, they took their tests indoors to a planetarium, where they had full control over the celestial environment. Surprisingly, when they dimmed the moon, the beetles still kept right on track. Only one other source of light remained to serve as their guide: it appeared the beetles were navigating by looking up at the Milky Way.
To be sure that this was really what was happening, the scientists needed to test the insects and limit their conditions. So they made the beetles wear little cardboard hats. This way, the researchers could see if it was in fact starlight and not some other sense that was guiding the beetles. Beetles in a control group were given clear plastic visors and could still see above them. The results were conclusive: the dung beetles wearing hats became disoriented and were unable to track their whereabouts; they rolled their dung balls around aimlessly. The control group rolled their balls almost perfectly straight ahead. These tiny Earthlings were using a distant galaxy as a compass.*6
The animal kingdom is full of marvels, but when it comes to the eyesight champion? A top contender has to be the dragonfly. The speed demons have twenty-eight thousand lenses per compound eye, which together make up the bulk of their heads. They also have unparalleled colour vision. While humans are trichromatic—we have three light-sensitive proteins, called “opsins,” that absorb red, blue, and green wavelengths, giving us the ability to mix as many as one million colours—some dragonfly species have up to thirty pigment opsins, allowing them to create a vast palette of literally unimaginable colours.*7 The insects can also see in ultraviolet and detect polarized light. In addition to all of that, they have another spectacular skill: they can see in slow motion.
To a dragonfly, like Neo in the film The Matrix, fast-moving bullets would appear slowed down, and what would appear as a speedy blur to us would be a crisp image. That’s because we see at about fifty frames per second while dragonflies see at three hundred frames per second. What looks like a movie to us would appear as a slide show to a dragonfly. Which is why it should come as no surprise that the insects are such formidable hunters; with their super-vision, they are able to catch 95 percent of their prey.
We will never completely know the world of wonder that is right in front of our eyes. Mostly, we can only guess what it might be like to see the world as other animals do. The closest approximation of how astonishing it could be might be likened to a colourblind person putting on EnChroma glasses and seeing colour for the very first time. Quite often, their jaw drops as they look around in utter amazement at colourful flowers and lush green trees. The experience can be overwhelming, and often they burst into tears.
Another glimpse of the world we’re blind to comes to us from people with a rare condition called tetrachromacy. Tetrachromats, as they are known, have a sort of hyper-colour vision, the ability to see a richer and more vibrant world than the average person can see. That’s because they are born with four different cone cells for colour vision whereas most of us have three. This fourth receptor allows them to perceive ninety-nine million more shades and hues than the average eye perceives. The genetic mutation is found in about 12 percent of women, but only a small sub-set of this group have true tetrachromacy.
So what does the world look like when it’s one hundred times more colourful? Tetrachromat Concetta Antico has described it as “seeing colors in other colors.” Compared to her, we see the world almost like the colourblind do. What is a grey pebble pathway to our eyes lights up in hers with a rainbow of different hues. As she describes it, “The little stones jump out at me with oranges, yellows, greens, blues and pinks.” Beyond an appreciation of beauty, this form of sight offers practical utility. When asked what she can see that others can’t, she has said, “I can tell if someone is sick just by looking at them. Their skin gets gray, it gets yellow, and there’s some green. I can tell when my daughter is sick because she will be all washed out and greenish-yellow or maybe whitish-lilac.” But we’ll never really know what she means, since she’s just using colour to describe another colour. And colour for her means something different from what it means for us.
Individuals with aphakia can also see beyond the ordinary. Like bees and eagles, they have the ability to see in ultraviolet. The condition is often a result of eye surgery, although at times it can be caused by a congenital anomaly. The term aphakia comes from the Latin, meaning “no lenses.” The reason most of us can’t see in ultraviolet is because the human lens naturally blocks out UV light. But patients who have undergone cataract surgery and had the lens removed can sometimes see into this range of the spectrum. Perhaps the most famous aphakic was Claude Monet. In 1923, at the age of eighty-two, the impressionist artist had his left lens removed during cataract surgery. When Monet began painting water lilies again, they were no longer white but had tints of deep purples and whitish blues. But again, we’re not seeing what he saw. He painted white lilies mauve and lilac, but mauve and lilac looked different to him than they do to us. Still, whatever colour the lilies were in his eyes, they were almost certainly not white.
By the Second World War, military intelligence had become aware of this real-world superpower and used aphakic patients as coastline lookouts. At the time, German U-boats used UV lamps to send covert signals to their onshore agents. The aphakics were enlisted to send in alerts when they saw the lights, which were invisible to everyone else. This should give us a pretty strong sense of the size of our perceptual blind spot. There can be enemies right off the coast, invisible to us but obvious to those who can see.
But not having the ability to see something doesn’t mean you can’t look. As an avid surfer, Mike Sturdivant had spent over thirty years in the water off the Gulf Coast of the United States. But in July 2010, something strange started to h
appen: he began coughing up blood. And Mike was not alone. Along the Florida beaches, people were starting to complain of shortness of breath, burns on their skin, and blurry vision. It was clear to Sturdivant that there was something in the water.
One night, he decided to take his UV light, which he used on his boat to check for engine leaks, to scour the beach and see what he could find. What he saw was confounding: from “the dune line to the water line,” the entire beach was glowing a bright orange.
Over two hundred kilometres away, cleanup operations were under way for the largest marine oil spill in US history. Over four million barrels of oil had spilled into the Gulf of Mexico from the Deepwater Horizon drilling rig, and an additional 1.8 million gallons of Corexit brand dispersant were poured into the water in an effort to make the oil degrade more quickly. Scientists would later discover that the combination of the oil and dispersant made the water fifty-two times more toxic.
Illuminated under a 370-nanometre UV light, the toxic mixture fluoresced. A year after the spill, Sturdivant partnered up with James Kirby, a coastal geologist at the University of South Florida, to begin a formal investigation. Over two years, the duo sent seventy-one samples to a lab for testing. The results were what they suspected.
Under the National Contingency Plan for responding to oil and hazardous waste spills, a beach is considered clean if it contains less than 1 percent of oil visible in a one-square-metre sampling area. But dispersant doesn’t remove oil; it disperses it. According to Sturdivant, that’s the problem: “The entire [cleanup] operation has been geared around making things invisible. And that’s why they’re using the dispersant. It’s not because it will help speed up the degradation of the oil. It’s because it makes it invisible.” That is, it makes it invisible to humans. Some animals, of course, can still see it perfectly well.