Aniamal Vision
We share this world with a variety of organisms from simple to complex life forms. They all are different in their features and capabilities. But do they experience the same world that we experience? Probably no. Every organism has different sense organs, very much different from ours and sees the world from its own perspective. Different animals and birds have got different types of eyes with different image processing capabilities. While some animals are color-blind, others can see the world in more detail than us. Some animals can see those color which we can’t and some can see the world in slow-motion. So, our eyes may be good in some aspects but there are some animals whose vision excel ours. Our visual perception of the outside world depends on how our eyes process light. Humans are trichromats – means that they have three types of photoreceptors known as “cones”, which can observe the colors red, green and blue. There is yet another type of photoreceptor cells present in our eyes called “rods”, which can detect small amounts of light; they help us to see things in the dark. Animals process light differently – some have only two types of photoreceptors (cones), which make them partially color-blind, some have four types of cone cells which enable them to see the ultraviolet spectrum of light and others can even detect polarized light i.e. light oscillating in the same plane. Some animals have a higher number of rod cells which enable them to see more clearly in the dark. Some birds have binocular eyes which can see minute objects miles away.

Thomas Cronin, a professor of visual philosophy at the University of Maryland, says:

“None of us can resist thinking that we can imagine what another animal is thinking.” [1]

While speculating what animals are thinking is a fantasy, viewing the world through their eyes is quite possible. We can do that by analyzing the properties of animals’ visual systems by the use of some advanced equipment.

So, how our favorite pets (cats, dogs etc.), birds, insects and aquatic animals see and perceive this vast and beautiful world? Let’s analyze their visual systems and other connected sense organs to find out.

Dog Vision


 

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Human View (Left) – Dog’s View (Right)

Unlike human beings, dogs have only two types of cone cells so they don’t see much variety of colors that we see. Their cone cells are sensitive to blue and yellow but not red and green. Their vision can be compared to a person who is color-blind. However, the popular belief that dogs can only see in shades of grey is simply not true. They can see blue and yellow and are less sensitive to shades of grey.

Also, their resolution of vision is lower than human beings. So, probably they cannot read the fine print in the newspaper. However, they can read the headlines. 😄 Human vision is among the sharpest of all animals, thanks to the tightly packed cones at the center of our retina. Again dog’s range of seeing objects clearer is around 6 meters whereas humans can see up to 23 meters.

But we cannot underestimate our little canine friend because of these limits. Dogs have a wider peripheral vision than ours. So they can see a much wider space at the time which helps them to protect themselves from possible threats around. Their limited sense of vision has empowered their other sense organs. They have a heightened sense of smell and a more sensitive ear which counters all the limits in the visual system.

Cat Vision


 

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Human’s View (Top) – Cat’s View (Bottom), also notice the area of Peripheral Vision | Wired

Dan-Eric Nilsson, a zoology professor and co-author of the book, “Animal Eyes”, says:

“We will never know what a cat would experience.” [2]

Like dogs, cats are also dichromats; they also have only two kinds of cone cells. Cats are also color-blind to red and green. To replicate a cat’s vision, one has to pool everything that is red or green into one color.

Cat’s eyesight also has a lower resolution due to which they see objects slightly blurred than we do. Although they have a blurry vision in the daylight, they have a sharper vision in the dark, thanks to the more amount of rods in their eyes. Also, cats can pick up quick movements more easily than humans. While humans have 180° of field of vision, cats visual field spans a whopping 200°. Also, cats have a larger peripheral vision.

So it turns out that, although cat’s vision is limited, it does surpass human eyes in some aspects.

Snake Vision


 

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Human View (Left) – Snake’s View (Right) | Nautilus

Snake vision varies wildly from snake to snake. Most of them have a low-resolution color vision during daytime and have a plenty of rod cells for sharper vision at night. Although they have a blurrier vision in the daytime, they can easily detect quick movements. So it’s better not to make a quick awkward movement when a poisonous snake is in front of you.

But what makes their vision special is their ability to sense infrared light. Most of the snakes, like viper, rattlesnake, python and boas, can detect heat signatures. They have special sensory tools called pit organs – a pair of holes on either side of the snout between the nostril and the eye. These pit organs are able to detect infrared light (heat signatures) which are then converted into nerve signals and reach the brain.

Snake’s brain merges the heat signals coming from pit organs with information from eyes so that prey’s thermal image is overlaid over the visual one. However, we can easily get an idea what a snake sees by looking through an infrared camera.

Fish Vision


 

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Human View (Left) – Fish View (Right) | ZME Science

Fish eyes have both cone and rod cells. They can see different colors just like humans. Some can even see ultraviolet light and some are sensitive to polarized light.

Although the eyes of fishes are similar to that of vertebrates, they have a more spherical vision[You may have seen fish eye effect in your digital camera.] Some deep-sea fishes have a larger number of rod cells which help them to see clearly in the dark.

However, there are some fishes like sharks which can’t see color. They see only in shades of grey, but clearer inside water.

Cuttlefish Vision


 

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Human View (Left) – Cuttlefish View (Right)

Seeing through the eyes of cephalopods such as octopus, squid or cuttlefish require a high range of imagination, as these sea creatures have evolved their eyes in the ocean separate from the vertebrates. For example, cephalopod eyes have no blind spot, and the pupil of a cuttlefish is shaped like a “W” making it look like an alien organism.

Despite being an expert hunter, cuttlefish have a blurrier vision than humans. Although they have incredible color changing skills (they can change the color patterns on their skin with a blink of an eye), they are totally color-blindTheir eyes have one photoreceptor that let them see in shades of grey.

They still have another pair of photoreceptors which detects polarisation of light. They can easily detect lights polarized in different orientation separately. Cuttlefish also produce polarization patterns on their skin which other Cuttlefish can easily observe through their vision. This may be a method of communication among them. Looking at one another they will see shades of grey with the polarization information overlaid, just like how snakes see the infrared information.

Snail Vision


 

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Human View (Left) – Snail’s View (Right)

Different types of snails have different types of eyes and visual capacity. As most snails are small it is difficult to see their eyes. But most of the land snails do have eyes. They are present on the top of the tallest pair of tentacles present on their head. The position of eyes also gives them a wider frame of vision.

On the other hand, sea snails have eyes in entirely different position. Rather than sitting on the tips of the tentacles, the eyes of sea snails are located at the base. Their eyes are locked in a position (just like humans have their eyes locked at the center of their face) and cannot move their eyes to see around like land snails. They are not yet another type of snails which don’t have eyes at all. These type of snails normally belong to the category of underground snails. However, it doesn’t mean that without vision they cannot move and perceive the environment. They can easily navigate their habitats through their sense of smell and touch. [3]

Actually, snails don’t rely on vision as much as humans, but it’s still one of their senses. Their eyes are very much primitive. They can neither see color nor focus on objects. Their vision is very much blurry; they can just make out whether another snail is moving past or a predator is approaching. However, snails can observe different intensities of light which help them to navigate towards dark places.

Bird Vision


 

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Human Vision (Left) – Reflected UV (Center) – Simulated Bird Vision (Right) | Credit: Dr. Klaus Schmitt, Germany

Vision is the most important sense for birds since a good eyesight is compulsory for a safe flight. So eyes of birds have evolved much and are superior to other vertebrates. Unlike humans, birds are tetrachromats – as they have four types of cone cells which enable them to see red, green, blue and ultraviolet simultaneously. Some of them have much sharper vision than humans, thanks to the presence of high-density cone cells in their retina. A large