HUMAN VISION V/S THOSE OF DOGS AND CATS

HUMAN VISION VERSUS THOSE OF DOGS AND CATS

Have you ever wondered how the world appears to animals with different eyes? Not just from another person's viewpoint, but from the perspective of a whole other creature. It's fascinating to discover that animals see the world in completely different ways than we do. Some have glowing eyes that allow them to see in the dark, while others have super-powered vision that can perceive colors beyond our imagination. Join me on this journey as we explore how different animals perceive the world around them.

Starting us off are the dogs. They love a game of fetch but have you ever noticed that sometimes when you throw something for a dog, they can’t seem to find it? It's all too obvious to you where it's lying in the grass, the dog keeps missing it. If the toy is red or green, then it may be almost impossible for your dog to spot it. That's because dogs are red-green colorblind. A bright red toy to them would appear a drab gray and would easily get lost in the equally gray-looking grass. That's because color vision is determined by special cells on the retina at the back of the eye, known as cones. Humans have three types of cone cells, blue, green, and red, which allow us to see all the colors in between.

But dogs only have two types of cone cells, which let them see blue and yellow, not red or green. When yellow light shines on these cone cells, neurons in the dog's brain get excited while neurons are suppressed when blue light hits the cones. A dog's brain interprets this excitation or suppression of its neurons as the sensation of yellow or blue colors respectively.

Meanwhile, red and green lights do not affect the dog's brain. With no signal to interpret these colors, they instead registered as gray. Have you ever noticed that dog never seems to recognize their owner from far away? It's only when they get closer that the tail wagging starts. Well, that's because a dog's vision is much blurrier than humans. Perfect human eyesight is 20/20, where you can see objects that are 20 feet away from you. Dogs are estimated to have 20/75 vision, meaning they have to be 20 feet away to discern details that most people can see from 75 feet. Now, you may be wondering if dogs have such blurry vision, then why are they used as guides for blind people?

Well, some dog breeds such as Labradors have vision closer to 20/20 accuracy and are most commonly used as seeing-eye dogs. Whereas other breeds such as German Shepherds, Rottweilers, and Miniature Schnauzers are more short-sighted at 20/75. Dogs may not be able to pass a letter eye test, but they have far better motion detection than humans. That's because dogs are descended from wolves and have eyes evolved for hunting on the move.

So for example, if a light bulb was flickering 60 times per second, humans would perceive the light as shining steadily. However, a dog's eyes could detect the light blinking. The light bulb would have to be flickering 75 times per second for the dog to perceive it as a constant light source. And whilst humans may need to turn on the lights in the evening, dogs can see things just fine. Dogs have far superior vision in low-light condition than humans do as they have far more rod cells which determine light from dark in their eyes than humans. So dogs' eyes aren't necessarily worse than ours, just adapted to view the world in a different way.

Moving on to cats, any cat owner will know that most cats will happily spend their days napping on the bed, sleeping in the sun, or loafing on the couch, but at night they'll spring into action, disrupting your sleep with their constant shenanigans, whether that's tapping your face or making a ruckus. Despite what it feels like, these late hour antics aren't because your cat wants to lose sleep, but rather cats are more active at night because they can actually see a whole lot better.

This is because of the distribution of cone versus rod cells than a cat's eyes. Cats have six to eight times more rod cells than humans do. As we know, more rod cells mean cats have superior vision in low-light conditions. It also means cats have better motion detection than humans because rod cells are fine-tuned motion sensors, being far more sensitive to light input than cone cells.

Rod cells are able to respond to individual particles of light known as photons, granting much better low-light vision. Cats' eyes also have a feature that gives them an extra advantage in the dark. If you've ever shown a torch at a cat, you've probably noticed the creepy, shiny effect in their eyes. That mirroring is because cats have a literal mirror at the back of their eyes, known as the tapetum. It's a layer of tissue that reflects light back onto the retina, allowing the eye to capture more light in dim conditions. So any intruding mice will have no chance sneaking around without getting caught at night. But despite being formidable foes at night, cats can't see too clearly during the day. That's because they have a limited number of cone cells and seeing bright light is a cone cell function.

Humans have 10 times more cone cells than cats do, and though cat's eyes have three types of cone cells, scientists are unsure if cats can see the full range of colors that humans can. It's suspected that their vision is limited to only blues and grays with far less richness and saturation in the colours. If you put this screen you're reading from on low saturation mode, it'd be similar to how your cat sees the world. Cats are also incredibly short-sighted. So while a human with 20/20 vision can see objects clearly at 100 to 200 feet away, cats can only see things as far as 20 feet away. So if you're standing across the room, your cat might not be ignoring you, but rather it's unable to see that you're there.

While humans can expand their pupils 15-fold, cats are capable of an unbelievable 300-fold change. But as cute as it looks, experienced cat owners know that they only get these overblown pupils when they're about to pour gah! Their ability to dynamically adjust their pupil size provides a distinct advantage in the role of predators. This adaptive feature allows them to accurately gauge distances and refine their depth perception, homing in on targets with precision.

Interestingly, domestic cats and their larger counterparts, such as tigers and lions, exhibit differences in pupil shape. While domestic cats boast slit-shaped pupils, big cats possess circular ones. Scientists attribute this divergence to the size of the animals. The theory suggests that larger cats, being elevated from the ground, don't require as many visual tricks to focus on prey as their smaller counterparts.

This unique insight prompts a reconsideration of cats' often perceived antisocial behavior. Could it be linked not to their personalities but to visual challenges? The notion sparks a humorous suggestion to train guide dogs for these short-sighted cats, although with a touch of skepticism.