I Spy With My Little Eye…
Eyes are incredible. That’s the only way that they can be described. The eyes are one of the select few organs that is common across multiple animal kingdoms. They have independently developed among a wide array of species close to 100 times, each with its own complex methodology of forming and interpreting images. This means that several species throughout the history of life on Earth all agreed that “seeing” was necessary for survival, some form of visual perception that could give them information to work with.
Eyes first appeared on Earth over 541 million years ago, during a time period known as the Cambrian explosion, aptly named for the exponential rate that evolution progressed. Eyes were a huge factor in survival and began in the form of eye spots in invertebrate animals such as planaria — simple flatworms who, when equipped with just the idea of if they were looking at something light or something dark, dominated their blind evolutionary rivals. Sight has continued to stand the test of time as one of the most important senses that we as life on planet Earth have.
Between generations of sighted animals, we as humans have developed our own organs to see, but there have been several that have developed eyes that far exceed the abilities of ours. Earth is filled with things to see, and life has created the organs and animals to perceive.
Being able to let in light into a visual medium and produce an accurate, reliable idea of the current environment was key for survival. If something wanted to eat you and saw you before you saw it, the situation did not look good for you (no pun intended). It created what zoologist Andrew Parker called an “evolutionary arms race” between species; any organism that didn’t have some way of sensing light was at a severe disadvantage. So evolution went hard at work, attempting to create a method of producing the most informative and precise images for an organism to then act upon. Some animals evolved around the idea that letting in as much light into the eye, then filtering through lenses to focus that image was the most successful methodology in creating visual feedback for life.
Acuity
Birds of prey have been gifted the best eyes on the planet. Their eyes are estimated to be four to eight times as strong as a human’s, able to spot prey from almost two miles away. That’s as if you were standing at one end of the Golden Gate bridge and able to see something at the other end with perfect clarity (assuming you have the ability to see through all the San Francisco fog). We revere the birds for their incredible visual abilities. People with sharp vision are commonly called “eagle-eyed”, or are compared to having “eyes like a hawk.” So how do we know that these birds of prey have better vision than us? Did we send eagles to the optometrist and make them read letters from an eye chart?
Not quite. First off, their retinas are lined with more light-detecting cells than us. Remember our eye spot fossil friends from before? Imagine having 200,000 of them. Per square millimeter of our retinas. These are called cones, and eagles have five times as many cones per square millimeter and can produce a sharper image out of what we as humans can see. A human eye and an eagle eye are roughly the same size, but eagles simply have more pixels to work with. Our 1080p to their 4K HD means they see a lot, and very clearly. The diagram below labels the fovea, a little dent in the back of our eyes and the sweet spot of vision. The fovea is the most cone-dense area of the eye, and light rays all converge on the fovea to place the observed object at the center of the image. While we have a small bowl-shaped dent in the back of our retinas, eagles have much deeper fovea, allowing them to be able to magnify the light and see telescopically.
They can also see a more subtle gradient of colors than we as humans or our most advanced computer programs can even visualize. Eagles form clear, crisp images in a multitude of colors, including UV light to track urine trails of their prey. To describe exactly how good their eyes are, imagine being able to spot a bug on the sidewalk from the 10th floor of a building, or being able to look intently at a player’s face from the back seats of the biggest football arenas in the country, and all this in more colors that you can possibly imagine. We have yet to develop cameras as good as capturing images as an eagle’s eye, and the complexity of how we interpret clear images is something scientists have yet to fully comprehend.
Motion
Why are flies so hard to swat? It seems that despite the human race’s superior cognitive capabilities and incredible physical feats of speed and strength, we still struggle mightily when forced into combat against these minuscule buzzing bugs. Humans have literally spent hours, days, possibly even years developing technology to eliminate flies, seducing them to their doom with traps or swatting them with electrified tennis rackets. However, if a person was stuck in a room tasked with catching a fly with no equipment, I doubt such an endeavor would end with success for most.
Flies seem to be all-seeing. Not only do they seem to know your next move and lazily avoid your onslaught of swats, but to make matters worse, they will consequently rub their legs together, almost as if plotting and scheming on how to annoy you even more. But how do they know? There’s no way that they can see the world at the same detail as we do and yet they seem to have super-human reactions to our movements, which turns out to be exactly the case.
Flies have compound eyes with thousands of visual receptors called ommatidia — each one an individual functioning eye. They act quite similarly to our eyes: the ommatidia receive light, filter it through a lens, determine the colors through the cones, and then send the image to the brain for interpretation. However, unlike our eyes, every individual ommatidia has a direct neural link to the brain, meaning that their eyes produce thousands of inputs per second for the fly.
Now your brain would be overwhelmed trying to understand thousands of images being sent to your brain at such a rapid pace, but fly vision is not as defined or as clear as human vision. They can only see a couple of yards away, but with their protruded sphere-shaped eyes, they are equipped with a greater range of sight and are even able to see objects behind them. Knowing all this, we may still be doubtful as to why we feel incompetent in trying to best a tiny creature with an even smaller brain, and quite frankly, it’s not even remotely a fair contest. Flies can slow down time.
Fusion Flicker Rate
Imagine staring at a clock. The seconds hand moves every second, as far as we’re concerned. Depending on an animal’s “fusion flicker rate”, that hand can actually be seen as moving faster or slower than we as humans can discern. Flies perceive each tick as moving four times as slowly. How is this possible? How is it that time “flies” for us, but not for the fly?
The fusion flicker rate is the rate at which an animal can distinguish distinct images, and is tested by seeing how quickly the animal can recognize a light being turned on and off before the flickering becomes perceived as a continuous stream of light. When our brain constructs vision for us, it is fed images at the flicker rate and then pastes them together to form a smooth video.
For humans, this rate is around 60 flashes per second, which is why watching 60 fps videos feels so fluid. For flies, this rate goes up to 240 flashes per second, with some species able to perceive up to 400 flashes per second, over six times the rate of a human.
This is why they can seem almost clairvoyant. No matter how quick we can try to move, the fly has already seen it. To survive, the fly behaves with an extreme caution: if any of its thousands of eyes detect motion too close, it takes off, regardless of whether the object will cause the fly harm. The fly most likely had time to read the headline of the newspaper you tried to swat it with before taking off.
Computer Vision
Fly vision is also a surprising subject of research for the technological future of sight: computer vision. Unlike flies, the computers have vast resources (computing power, energy, etc.) to enable them to make much more out of the information that it captures. However, in terms of efficiency and speed, the fly’s perception of motion is king. The highly specialized neurons for vision and relative ease of image flow through the fly’s nervous system is unmatched in modern computing, let alone in a computer as small as a fly’s brain.
Scientists are sifting through the fly’s nervous system on the cellular level, trying to understand the intricacies of the incredibly effective motion detection systems that nature and evolution granted them. With these discoveries, computer vision can improve in its reactions to motion, an essential component of self driving vehicles.
When we consider the artificial intelligence aspect of computer vision, we attempt to solve two problems: the engineering problem of commanding a system to work in an expected manner as well as emerge with the comprehensive understanding of how the system functions, specifically what features are necessary to display an all encompassing mastery of the problem.
When humans first attempted to fly, we tried to model our machines after animals that we saw flying, and thus made mechanisms with wings that could flap. Through experimentation and iteration, we discovered principles of aerodynamics and consequently created vehicles with wings shaped to generate lift, allowing the plane to fly.
Mastering computer vision would demonstrate functional proficiency but also a comprehensive definition of what it means to “see”. We have been making leaps in progress in developing this technology, but the biological eye remains more mechanically advanced than anything we as humankind have ever created.
