How animals view the world

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Cat

You may have wondered how a cat sees the world. Cats perceive their surroundings somewhat less detailed than humans, but they are clearly superior to humans when it comes to seeing at dusk. Additionally, they have evolved beyond us as far as the size of the visual field is concerned. While humans reach about 180 degrees with our visual field, the cat sees 200 degrees of its environment.

Not so good, on the other hand, is their ability to distinguish colours from each other. This is because cats lack the responsible photoreceptors, so-called cones, on the retina. In addition, their cone types differ from those of humans. Have you ever noticed that cats never blink? They don't have to. The reason for this is their three eyelids: an upper movable eyelid, a lower immovable eyelid and a third eyelid - the so-called nictitating membrane. This ensures that the eyeball is always kept sufficiently moist.

Sources:

http://www.spiegel.de/fotostrecke/kunstprojekt-kaetzchens-fehlende-weitsicht-fotostrecke-102734-4.html
https://www.businessinsider.de/pictures-of-how-cats-see-the-world-2013-10?r=US&IR=T
https://www.livescience.com/40460-images-cat-versus-human-vision.html

Dog

The myth persists that the world through the eyes of a dog is no more than monochrome. However, this assumption was refuted at the end of the 20th century. It was proven that dogs can see colour, just differently. Dogs see colours, but different. As a result, a dog's vision is similar to that of a human with red-green vision impairment. So, our four-legged friends perceive everything that is red as yellow tones whereas green is not coloured for them. In the darkness, dogs can recognise far more than humans. The reason for this is the higher number of rods, i.e. photoreceptors, which are responsible for the light sensitivity of the eyes. Thanks to the invention of HDTV, dogs are now also in the fortunate position of being able to watch TV. What used to seem like stroboscopic light to them can now be seen more clearly thanks to the higher frame rates. By the way, dogs like pictures of other dogs the most. So bear this in mind when selecting the film!

Sources:

https://dog-vision.com/
https://www.derhund.de/so-sehen-hunde/
https://www.animalwised.com/what-do-dogs-see-2398.html

Snail

Without a magnifying glass, the eyes of a snail are no more than two small black dots at the tip of two antennae. As the name suggests, the snail "feels" the world around it with its feelers. If it encounters an obstacle during its exploration, the telescopic eyes are retracted in a matter of seconds. It is now known that the development of the snail's sense of sight is closely related to its evolution and way of life. Snails cannot perceive more than a few centimetres in front of it, which explains why the eyes shrug back when the snail encounters an object.

It was thought that snails only see the world in black and white. However, it has been observed that snails prefer green plants, while they are more likely to avoid red and brown tones. What is certain, is that they can distinguish between dark and light. And it is not only sight that snails use their feelers for, but also their sense of smell. Fortunately for the snail, it is not very dependent on its eyes. With an average speed of three metres per hour, it has enough time to explore its environment in peace.

Sources:

https://www.nhm.ac.uk/discover/how-do-other-animals-see-the-world.html
http://www.weichtiere.at/Schnecken/weinbergschnecke.html?/Schnecken/land/weinberg/seiten/sinne.html

Bee

To bees, the world appears like a large pixel picture. The reason for this is its two large facet eyes, which are in turn made up of several thousand individual eyes. Since the eyes on their head are placed on a hemispherical surface, it is possible for bees to capture a large viewing angle, even if they cannot see sharply. On the other hand, they can see up to 300 images per second, while humans can only see about 65. This high image capacity helps bees perceive movements much better. Visual impairments also exist in bees. They are red-blind, meaning they perceive red tones as black, which is why they prefer colours such as blue and yellow. Where they have the edge over us, is the ability to recognise ultraviolet light. Flowering plants take advantage of this by reflecting the ultraviolet light of the sun through pigments. This signals to the bee, in search of food, that this is a suitable place to land. There are also differences between types of bees in terms of vision. The eyes of drones are much better than those of workers or queens. The queen spends most of her time surrounded by darkness, inside the beehive.

Sources:

https://beecare.bayer.com/medien/beenow/detail/sehforschung-wie-bienen-die-welt-sehen
https://www.beeculture.com/bees-see-matters/

Human

The healthy human eye is able to absorb more than ten million pieces of information every second, transmit them to the brain and process them there. Approximately 95 percent of our vision and performance is provided from one point in the eye: the macula, also known as the yellow spot. The macula forms the centre of the retina and helps us, among other things, to see sharply and in colour, as well as to distinguish between light and dark. The more than 100 million photoreceptors that make up the retina are divided into two significant types: Cones and rods. The cones are more sensitive to light and help us to perceive colours. The rods are responsible for our twilight and night vision. Like any organ, the eye can also develop deficits.

People with the diagnosis "near-sightedness", also known as Myopia, find it difficult to recognise things in the distance, but at a closer distance they can see perfectly. Myopia is usually caused by an eyeball that is too long or a refractive power of the lens that is too high. To be able to see clearly, the light rays arriving in parallel must be bundled and refracted exactly on the retina. In a near-sighted person, however, the light rays meet before the retina. Far-sightedness, on the other hand, is characterised by the ability to see objects in the distance without problems, but the exact recognition of objects up close is difficult. The effect in the eye also behaves the other way round: the eyeball is usually too short or the refractive power of the eye too weak to concentrate incident rays in the retina. The light is therefore bundled only behind the focal point. Red-green weakness, which makes it difficult for people to distinguish between the colours red and green, occurs more frequently in men. This is because the genes for the red and green cones are positioned on the X chromosome. Men only have one X chromosome, meaning they are more likely to be affected by this genetic defect than women, who can still see normally due to their two X chromosomes, even in the event of a genetic defect on one of the chromosomes.

Sources:

https://www.livescience.com/32559-why-do-we-see-in-color.html
https://www.planet-wissen.de/natur/sinne/sehen/index.html

Lensbest - International Day of Biological Diversity

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