Do all animals see in colour?

The world we live in is a myriad (great amount) of colours. Everywhere we look, we can see spectacular hues of reds, greens, blues, yellows and so on. These beautiful colours are naturally attractive and very pleasing to the eye.

We humans are fortunate in being able to see and appreciate these wonderful colours. It is due to the type of vision humans are endowed with that we can see the world in colour. However, not all the species in the animal kingdom can see in colour. So, let’s examine which animals cannot see colours and why.

The colour vision and perception (knowledge of something through senses) across the animal kingdom is the subject of much ongoing research because it is not easy to determine what a particular animal sees through its eyes.

We obviously cannot see through their eyes, so scientists can only make an educated guess about the visual spectrum of animals based on the various tests and research carried out over the years.

According to scientific research, perception of colour is determined by the presence of cone photoreceptors within the retina. If you are not aware as to what the retina is, it is the layer at the back of the eyeball which is sensitive to light.

The eyes of most animals contain an optical system that produces an image of the world onto a large number of light detectors.

Studies have shown that we detect light with our eyes, but we see with our brain. Light signals received by our eyes are sent to the brain. The brain then decides, with the aid of previous experience, what we are looking at. It is this process that is called perception by scientists.

Many scientists believe that animals understand very little of what they actually see. In fact some have the view that animals see things the way some humans see abstract paintings, rarely understanding what the artist is trying to portray.

Even though the understanding about animal vision is limited, what the scientists have discovered so far is very fascinating.

However, some claim that what we know about colour perception in animals pales in comparison to that yet to be discovered.

An animal can see in colour if it can differentiate between different wavelengths, according to scientists. They have discovered that though mammals have relatively weak colour vision, humans and other animals that are known as primates within the mammalian family have the most advanced colour perception within this class.

Old World primates such as the great apes, macaque and monkeys have colour vision based upon three different cone types which are very similar to that of most humans. Mammals that are not primates have only two cone types.

Scientists have discovered enormous diversity in the retinal structure and neuronal mechanisms within the animal kingdom. It is a known fact that the position of the eye within the head determines the degree of peripheral (surrounding region) vision. The binocular vision is also necessary for the judgment of distance.

Many of you who have cats and dogs as pets would be now keen to know whether your beloved pets could also see the world as you see it....in colour! Well, until recently it was commonly believed that our canine friends could see only black and white.

And so, it was believed that dogs saw the world the way we see black and white photographs, but not as distinctly.

However, recent studies have revealed otherwise. Those of you who were so far not aware of this fact are bound to be excited to learn that your doggie friends and cats too have some degree of colour vision. Tests carried out on dogs have revealed that they can distinguish the colours red and blue, but are often confused with red and green.

It is generally accepted that their colour spectrum is very limited. Even though blue may be visible, colours such as red, green and yellow may appear similar to them. They are believed to be colour blind, like some humans who also cannot differentiate between red and green. However, don’t think that what your pet dogs see is as vibrantly coloured as what you see.

What they generally see are pale shades of colour, more like a washed out image of what we humans see. But, dogs have better night vision. They also have a higher vision field than that of humans; dogs have their eyes set on either side of their head, so their vision field is 240 degrees compared with the 200 degree vision field of humans. Dogs can distinguish an object that humans could see at 90 feet, only at 20 feet!

The colour vision of cats is believed to be poorer than that of dogs since they rely almost entirely on rod cells for their vision. But in general, cats can see as well as humans. Cats appear to be slightly near sighted because their vision is tailored more for closer objects. Cats have an elliptical pupil which opens and closes much faster than round types of pupils. This allows for a proportionately larger pupil size, letting in more light.

Even though most cats detect very little colour they can see much better at night than humans, with eyes that are very sensitive to movement.

Cats have two distinct types of light sensitive cells in the eye (retina) like humans have. They are rods and cones. Rods are receptors used by the eye in the night, especially to detect movement. Cones are used during daytime to process information. The ratio of rods to a cone in cats is 25:1 while it’s 4:1 in humans.

It is a fact that cats have visual acuity (ability to focus) that is much greater than that of humans, and also that they can see better than us in the night. But, even cats need some glimmer of light to see at night.

Now that we know something about how cats and dogs see the world, let’s check out about some other animals next week.

Facts and pix: Internet.

---------------------

Fast facts

* Humans have colour vision produced by three different retinal cone cells called trichomatic vision. Our colour sensitivity extends to three different wavelengths of light; red, green and blue.

* Ultraviolet light lies beyond the blue, indigo and violet end of the visible spectrum of electromagnetic radiation.

* Light at the far-end of the so-called visible spectrum has the longest wavelength of all-around 0.73 to 0.8 micrometres. It’s not visible to human eyes, but some animals, including the dragonfish can see it.

* The visible spectrum comprises seven colours-red, orange, yellow, green, blue, indigo and violet - the colours of the rainbow.

* Electromagnetic radiation consists of the energy waves associated with electric and magnetic waves, and results from the acceleration of an electric charge.

* The types of electromagnetic radiation are radio waves, infrared, visible light, x-ray and gamma rays.

------*****