Rods in the eye – the world of colors

Everybody knows that poppies are bright red, grasses are green and lemons are yellow. Why should animals see it differently? "Because the world is not really colorful, but only looks that way to our eyes", explained Professor Christa Neumeyer to many astonished children who came to the Children’s University in Mainz despite the onset of winter.

Rods in the eye - the world of colors

In the eyes of most animals, the world looks very different from the way we know it. (Source: Johannes Gutenberg University Mainz)

Our eyes deliver all kinds of impressions to the brain. We then perceive this information as colors and shapes. However, many animals have completely different eyes than we do, with which they also see the world completely differently.

"The eyes of cats are still similar to ours", explains Christa Neumeyer and shows the children’s uni participants photos of a big cat’s face. "In contrast, the differences in other animal species are enormous." Spiders for example have eight eyes, bees have two "compound eyes", and night monkeys have eyes, with which they can recognize everything exactly even in darkness. But how can it be proven that these animals actually see differently from humans??

The answer of the animals

Rods in the eye - the world of colors

Professor Christa Neumeyer has explained to children how researchers can understand the answers of animals. (Source: Bright Mind)

Since we can’t look at the world through the eyes of animals, we’ll have to find another way to answer this question. Christa Neumeyer knows what to do: "You have to ask the animal and then understand its answer." Aha. The faces of the young students reflect perplexity. Someone whispers: "Talking to a bee? That is not possible at all!"

But there the child student is mistaken. In 1914, an animal scientist proved that it is possible after all. Of course, you can’t ask a bee: "Hey, tell me, how do you actually see the world??", and then expect an answer. But you can ask the bee a task and then read the correct answer from its behavior. In an experiment devised by Karl von Frisch, bees indicate whether they can distinguish blue from other colors.

Experiment with bees

Rods in the eye - the world of colors

Bees land unerringly on the area with the sugar water. Because they have memorized the color. (Source: Johannes Gutenberg University Mainz)

It works like this: First, an area is divided into colorful fields. So now there is a yellow, a red, a green, a violet and other colored boxes. Now a small bowl with normal water is placed on each field. A small bowl with sugar water is placed only on the blue field. Sweetened water has the advantage that it tastes very good to the bees, but – in contrast to honey – they cannot smell it. In this way it is excluded that bees follow their sense of smell instead of their eyes.

Now a captured bee in a matchbox is placed on the blue field. The box must be opened very carefully just enough for the bee to stick out its antennae and head and reach the sugar water. When the bee realizes what deliciousness is waiting for it, it doesn’t want to escape anymore. Then you can safely leave them completely free.

Where has the sugar water gone?

She is now so busy drinking sugar water that you can easily paint a small white dot on her to recognize her again later on. When the insect has drunk enough, it flies away to inform the other bees about its find.

Before the bee comes back now, you have to reshuffle the colored area so that the blue field is in a completely different place than before. If the bee now nevertheless flies again to the blue square to drink sugar water again, then this is the proof that it can distinguish this area from the other ones. And indeed: The bee with the white point heads determinedly for the blue field.

Black and white or color?

Rods in the eye - the world of colors

The field at the bottom left has the same brightness as the blue square. Bees still don’t get confused. (Source: Children’s University Mainz)

So now it is proved that the bee can distinguish one field from the others. But whether it actually recognized the color blue is still unclear. Because the different areas can also be distinguished on a black and white photo, on which different colors have been converted into different shades of gray. So do bees actually see in color, or do they perceive the world through different levels of light and darkness?

To verify this, the experiment must be repeated in a slightly different way. Instead of colorful color tiles, except for the blue one, there are now only gray tiles on the table. One of these gray plates has exactly the shade of gray that the blue plate in the black and white photo would have. If the bee could not see any colors, then it would have to be confused and fly indecisively back and forth between the blue and the dark gray field. But the bee is heading again for the blue field. This proves that it can actually see colors.

Ultra-violet is invisible to the human eye

Rods in the eye - the world of colors

The honey bee’s compound eyes see the world colorfully. However, they do not detect dark red, but they do detect ultraviolet. (Source: Wikipedia)

Karl von Frisch has of course also tested whether bees can recognize further colors. In the process, he discovered something surprising: Bees can distinguish all colors – except dark red. That looks just like black to them. Instead, they see a color that we cannot recognize: ultraviolet. For people are "UV rays on the other hand only in a very special light visible.

"Everything in nature has a meaning", said Professor Neumeyer. Because bees recognize UV light, yellow flowers do not all look the same color to them as they do to us. Bees recognize in a flash which yellow flower they have to fly to because it contains a lot of nectar.

Goldfish are a "Mainz specialty"

Rods in the eye - the world of colors

Goldfish go directly to the tube with the correct color point. (Source: Johannes Gutenberg University Mainz)

By the way, this lecture is not only about the bees’ point of view. Julia had been waiting all along for when she would finally learn about her favorite animals – and they are fishes.

Your patience has been rewarded. "Fish are the specialty of animal researchers at the University of Mainz", reported Christa Neumeyer. "We from Mainz have found out that they can also see the color ultraviolet." This had been a big surprise for many natural scientists.

The goldfish experiment reminded strongly of the experiment with the bee. The fish are not attracted with sugar water, but with a food paste. If a fish has learned that there is food at the blue spot, it will target this spot again the next time. With this experiment, scientists have proven that goldfish can even see better under water than people wearing diving goggles.

Why do we see colors?

Rods in the eye - the world of colors

This flower is yellow. Bees, on the other hand, see ultraviolet (right). Humans, however, cannot recognize this color. (Source: Johannes Gutenberg University Mainz)

To understand why some animals can see ultraviolet and others can’t, we have to take a very, very close look at the eyes. Tiny cells on the retina of the eye are responsible for our ability to distinguish between different colors and brightnesses. Some of these cells have the shape of "rods", others that of "cones. With the help of the "rods we can distinguish different levels of brightness. The "cones are responsible for color perception. There are three different types of cones in the human eye.

The first type of cones is specialized on short wavelength light. These cones transmit incoming information to the brain, where it is interpreted as "blue" can be decoded. The second type of cone is responsible for the middle wave range. When he reports, the brain interprets this information as "green". And the third cone finally reacts to the long-wave light. Our brain concludes: "red.

When the medium-wave and the long-wave cones report at the same time, we get the impression that we are "yellow" see. If all three cone types rain at once, our brain concludes: "white". If, on the other hand, no cone is activated at all, we interpret this as "black". When we "black see, then we see nothing at all. With some animals it is different. You have an extra cone. When the fish responds, the color "ultra-violet" is created in the brain.

Some people have only two cones

Rods in the eye - the world of colors

If you read 31 instead of CH, you can hardly distinguish between red and green. (Source: Dr. med. Rudolf Fischl)

Because all types of rods and cones are distributed all over the retina, the brain receives an incredible number of messages at the same time – at least when we have our eyes open. In the brain, the individual pieces of information are then combined to form a picture of the environment.

Five out of one hundred people, however, cannot distinguish between red and green at all or only poorly. This is due to the fact that one type of cone has completely or partially failed in them. If you belong to this type, you can test with the picture on the right side. If everything in your eye works normally, then you should see the letters "CH" clearly recognize. If you, on the other hand, see a "31 then you are probably "red-green-blind". But that doesn’t matter at least if you don’t want to become a pilot later on. By the way, dogs have the same problem. They are also unable to distinguish between red and green areas, since they only have two types of cones in their eyes.

Particularly good and bad eyes in the animal kingdom

Rods in the eye - the world of colors

At the end, Professor Neumeyer had to explain how the children’s pets see the world. (Source: Bright Mind)

At the end of the lecture, the young students learned which animal species can see what. Monkeys, kangaroos and fire salamanders see the world almost like we do. They have the same three cones in their eyes as humans do.

Some animals have an additional type of cone that can see ultraviolet light. With four cones, these animals see their environment much more clearly than humans do. This means, for example, that almost all birds can distinguish ripe from unripe fruit very quickly, as the ripe fruit shines much more brightly in their eyes. Besides birds, most reptiles and many fish also have four cones.

However, there are some species in the animal world that cannot distinguish colors at all. Since dolphins and night monkeys have only one type of cone, they perceive their environment in different shades of gray. As a "small compensation but their rods are extremely well developed. This allows them to orient themselves easily even in the dark.

Don’t forget to look at the photo gallery in the upper right corner with many more pictures and information.

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