How do you check how many cones you have in your eye?

How do you check how many cones you have in your eye?

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Following my previous question: What color does the other cone in Tetrachromacy correspond to?

People with normal color vision posses 3 cones in their eye. But there are some rare cases when people can have 4 cones (Tetrachromacy). These people, some of them will notice the shades difference in the scene through their eye. And the rest won't notice it, because simply their 4th cone is activated in the close peak value with the the L-cone. Therefore eye will not find any difference and will encode only one color even if it's coming from 2 cones stimuli.

How do you check, to know how many cones you have in your eye ? If the case is, even people who posses 4 cones can't even notice the shades difference ?

One of the two confirmed cases of tetrachromacy was confirmed genetically:

From this Popular Science article:

Based on Antico's genes, Jameson has determined that Antico's fourth cone absorbs wavelengths that are "reddish-orangey-yellow, but what it appears to Concetta is uncertain at the moment," she added. Since the tests aren't calibrated for this wavelength, empirically demonstrating tetrachromacy is still really difficult.

Color vision is connected to the X chromosome and mutations in the X chromosome cause less or more color vision. In the above case, the theory that people with 2 mutated X chromosomes could have four cones instead of three was tested.

This image from Scitable by Nature Education articles simulates regular vision on the left and tetrachromatic vision on the right:

As far as how to test to see how many cones you have, there are some online test that may or may not be very reliable. This Metro news article has a test produced by Professor Diana Derval, author of "DesigningLuxuryBrands: The Science of Pleasing Customers' Senses. However, due to the limitations of computer screens it would not be reliable to test for tetrachromacy.

This fascinating test helps you find out how many colours you can see

It's become apparent that the ability to see various colours varies widely from person to person. The reason for this stems from differences in the number of cone cells each of us has inside our eyes. These cells function as photoreceptors the number you have affects how many colours of the visible light spectrum you can pick out.

The simple test published below was created by Professor Diana Derval. Answer the question and then check the answers, and you'll be able to find out how well you see the world around you - and how much your perception differs from other people.

Count the number of colours and shades you can see in the spectrum:

Less than 20 colours: You're a dichromat. This means that you have only two types of cone cells. 'However, don't worry - you're in good company here, since dogs have exactly the same kind of vision', jokes Professor Derval. Perhaps you like to wear black, beige or dark blue coloured-clothing most of all. Twenty-five percent of the world's population are dichromats.

Between 20 and 33 colours: You have trichromatic vision. This means your eyes have three types of cone cells. You are able to perceive purple, dark blue, green and red colours well. This is great - 50% of the world's population have the same kind of vision as you.

Between 34 and 39 colours: Wow! You have tetrachromatic vision. Much like bees, you possess four different kinds of cone cells in your eyes and see the majority of colours in the visible light spectrum. The chances are you're not a fan of yellow and you have next to no yellow clothing in your wardrobe. Only 25% of people can see all the colours in the spectrum.

It's always interesting to compare your results with friends. Perhaps you've been close to a tetrachromatic person all your life and have never known just how special they are!

How Does Your Eye See Colors?

Think of your eye as a camera. The front part has a lens. Its job is to focus images on the inside of the back of your eye. This area is called the retina. It’s covered with special nerve cells that contain pigments that react to light:

Cones control your color vision. There are several kinds of pigments present in three types of cone cells. Some react to short-wavelength light, others react to medium wavelengths, and others react to higher wavelengths

Rods only have one kind of pigment. It reacts the same way to any light wavelength. Rods don’t have anything to do with color vision. But they are very sensitive to light and allow us to see at night.

Tetrachromat Test Online Asks 'How Many Colors Do You See?' Viral Quiz Claims To Check For Tetrachromacy Vision

What color is that dress? That question is so last week. Now, the next viral fad is to take a tetrachromat test online to see if you are indeed blessed with a fourth eye cone that gives you tetrachromacy vision. But is there actually anything to the online tetrachromat test?

In a related report by the Inquisitr, the dress debate has eye doctors weighing in on the controversy with a bit of science, but reddit claims they've found both white-gold and blue-black versions of the same dress, even though the manufacturer supposedly claims only the latter version exists.

This particular color test started on LinkedIn, with someone calling themselves Professor Diana Derval asking how many colors can you see in regards to the above image. The idea is that if you can visually count more than 32 colors, then you have tetrachromacy vision, which supposedly means you have a fourth cone in your eye.

In practice, this means a tetrachromat can see a whole lot more variations of color than one of us plain ol' trichromats. If you only see less than 20 color variants, then your vision is supposedly dog poor, meaning you are a dichromat, who likely enjoys wearing black, beige, and blue. At least this explains that dress (that's a joke).

The online tetrachromat test also claims that 25 percent of the world population is a tetrachromat, which would explain why so many friends on Facebook suddenly developed tetrachromacy. If you pass the tetrachromacy test, it's claimed you are likely irritated by yellow, so this color won't be found in your closet.

But is any of this actually true? Jay Neitz, a researcher at the Medical College of Wisconsin, estimated that half of the world's female population does indeed have a fourth cone, but this hardly makes them a tetrachromat. It's believed only a small percentage of women can actually see extra colors in our world, and the odds of being a male tetrachromat are estimated to be very low.

In addition, the tetrachromat test fails for one simple reason: computer screens, even those fancy high contrast LED screens, are simply not physically capable of displaying the full range of light, according to New Castle University's Tetrachromacy Project.


Last week, everyone was talking about the blue/black or white/gold dress.

However, many people still couldn’t grasp why they saw the dress different than others.

An expert in neuromarketing created a post on LinkedIn explaining the basics of vision.

In the article, she posted a color spectrum similar to the one below.

(Click on the image to make it appear larger.)

Readers were asked to count how many different colors they saw in the spectrum.

If you see less than 20 colors, you are like 25 percent of the population and dichromat.

Dichromats have two types of color receptors.

Derval says dichromats are likely to wear black, beige and blue.

If you see between 20 and 32 colors, you have three types of color receptors.

About 50 percent of the population are trichromats.

If you see between 33 and 39 colors, you are a tetrachromat and have four types of cones.

Derval says tetrachromats are irritated by the color yellow but are less likely to be tricked by the blue/black or white/gold dress, no matter the lighting.

Can humans ever directly see a photon?

Yes. In fact, photons are the only things that humans can directly see. A photon is a bit of light. Human eyes are specifically designed to detect light. This happens when a photon enters the eye and is absorbed by one of the rod or cone cells that cover the retina on the inner back surface of the eye. When you look at a chair, you are not actually seeing a chair. You are seeing a bunch of photons that have reflected off of the chair. In the process of reflecting off of the chair, these photons have been arranged in a pattern that resembles the chair. When the photons strike your retina, your cone and rod cells detect this pattern and send it to your brain. In this way, your brain thinks it's looking at a chair when it's really looking at a bunch of photons arranged in a chair pattern.

Your eyes can see bunches of photons, but can they see a single, isolated photon? Each rod cell in your eye is indeed capable of detecting a single, isolated photon. However, the neural circuitry in your eye only passes a signal along to the brain if several photons are detected at about the same time in neighboring rod cells. Therefore, even though your eye is capable of detecting a single, isolated photon, your brain is not capable of perceiving it. If it could, an isolated photon would just look like a brief flash of brightness at a single point. We know this because a sensitive camera sensor is indeed able to detect and process an isolated photon, and the photon just looks like a brief flash of brightness at a single point.

A photon has several properties, and each of these properties carries information about the source that created the photon or the last object that interacted with the photon. The basic properties of a photon that carry information are color (i.e. frequency), spin (i.e. polarization), location, direction of propagation, and wave phase. There are also many other properties of a photon such as energy, wavelength, momentum, and wavenumber but these are all dependent on the frequency and therefore do not carry any extra information. Additionally, when many photons are present, information can be carried by the number of the photons (i.e. brightness). When a group of photons reflects off of a chair, the photons form patterns of color, spin, location, direction, wave phase, and brightness that contains information about the chair. With the proper tools, each of these patterns can be analyzed in order to gain information about the chair. The human eye is designed to detect the color, location, direction, and brightness patterns of a group of photons, but not the spin or wave phase.

Color information is detected in the eye by having three different types of cone cells that each have a different range of color sensitivity. One of the types has a sensitivity range centered on red, another type has a range centered on green, and another type has a range centered on blue. The eye can see almost all of the colors in the visible spectrum by comparing the relative activation of these three different types of cone cells. For instance, when you look at a yellow tulip, yellow photons stream into your eye and hit your red, green, and blue cone cells. Only the red and green cone cells are triggered by the yellow photons, and your brain interprets red plus green as yellow. In contrast to cone cells, there is only one type of rod cell, and so the rod cells can only detect brightness and not color. The rod cells are primarily used in low lighting conditions.

Location information is detected in the eye by having the cone and rod cells spread across different locations along the retina. Different photons existing at different locations will trigger different cells. In this way, the spatial pattern of photon location is directly detected by the retina. Note that photons can come from many different directions and blur together. For this reason, the eye has a stack of lens in the front which focuses only the light to a certain cell which comes from a single point on the object being viewed. The lens plays an essential role in extracting location information about the object being viewed from the location information of the photons on the retina. If the lens malfunctions, photon location on the retina no longer corresponds exactly to point locations on the object being viewed and the image ends up blurry. Note that the human optical system can only directly image two dimensions of the photon location information. Information about the third dimension is indirectly extracted by humans using a variety of visual tricks (called "depth cues"), the main trick being the use of two eyes that are slightly offset from each other.

Direction information is only crudely detected by humans by having the brain keep track of which way the eyes are pointed, and by having the eyes look at an object from many different angles. For instance, a room with one wall painted red and the opposite wall painted blue has red photons from the wall shooting in one direction and blue photons from the other wall shooting in the opposite direction. At a given spot in the room, the bunch of photons at that spot includes red photons and blue photons traveling in opposite directions. However, a human can only deduce that the red and blue photons are traveling in different directions (and therefore deduce that the red and blue walls are at different locations) by turning his head and analyzing two different views while his brain tracks the orientation of his head.

Brightness information is directly extracted by the retina by measuring how many photons strike a certain region of the retina in a certain time increment. Both the rod cells and the cone cells can collect brightness information.

Since the human eye ultimately only sees photons, a light-generating machine can make a physical object seem to be present by recreating the correct patterns of photons that would come off of the object if it were really present. For instance, we can make it look like a chair is present if we create a collection of photons with the same patterns as the collection of photons that is present when a chair really is there. This is what computer display screens do. A camera captures the patterns in the photons coming from a chair and stores the information as bits of electricity. A computer screen then uses this information to recreate the photon collection and you see a picture of the chair.

However, standard computers screens can only specify the color, brightness, and two-dimensional location of the photons they create. As a result, the image of a physical object on a computer screen is two-dimensional and not completely realistic. There are many tricks that are used to try to convey the third dimension of information to humans, including the polarization glasses used in 3D cinemas and the lenticular lenses used on some book covers. However, such systems are usually not entirely realistic because they do not actually recreate the full three-dimensional photon field. This means that such "3D" recreations of objects can only be viewed from one look angle and are not entirely convincing. Some people find that because such "3D" systems use visual tricks rather than a full three-dimensional photon field, these systems give them headaches and nausea.

In contrast, a holographic projector comes much closer to recreating the full three-dimensional photon field coming from an object. As a result, a hologram looks much more realistic and can be viewed from many different angles, just like a real object. However, true holograms are currently not able to effectively reproduce color information. Note that many color-accurate images that are claimed to be holograms are actually flat images with tricks added in to make them look somewhat three-dimensional. A fully-realistic photon recreation of a physical object will not be possible until holograms are able to accurately recreate color information.

The two properties of photons that human eyes cannot see are spin (i.e. polarization) and wave phase. Note that under the right conditions some people can detect the overall polarization state of an entire light beam but no naked human eye can directly see the polarization pattern. By looking through rotatable polarization filters, which convert polarization information to color intensity information, a trained human can learn to indirectly see the polarization pattern of the photons coming from an object. An example of this is the photoelasticity method which allows people to see mechanical stresses in certain objects. In contrast to humans, some animals such as honeybees and octopuses can indeed directly see the polarization pattern of a collection of photons. For instance, honeybees can see the natural polarization pattern that exists in the daytime sky and use it for orientation purposes. Photon wave phase can also not be directly detected by humans but can be detected by machines called interferometers. Phase information is often used to determine the flatness of a reflecting surface.

In summary, humans can indeed see photons. Humans can see all of the properties of photons except for spin and wave phase. Since photons travel in patterns dictated by the source that created them or the last object that the photons interacted with, we usually don't realize we are looking at photons at all. Rather, we think we are looking at the physical objects that are creating and scattering the photons.

Now, perhaps you meant to ask, "Can humans ever see a photon in the same way we see a chair?" Again, we can see a chair because photons bounce off of it in a certain pattern representative of the chair and enter our eyes. In order to see a photon in the same way you see a chair, you would have to have a bunch of photons bounce off of the one photon you are trying to "see" and then have this bunch enter your eye. However, photons never directly bounce off of each other, so this could never work. Even if photons could bounce off of each other, you would not see anything special from this setup. You would still just see a flash light at one point when the small bunch of photons strikes your retina. When you think you see a light beam sitting out in space, such as coming from a flashlight, you are in reality seeing the dust particles along the path of the beam because of the photons bouncing off of the dust particles.

IGame Eye Test

Eye Test is a simple game that tests how well you can differentiate between slight variations of the same color. It does this by presenting you a square grid of smaller squares all seemingly the same color except one. Each step adds more squares and reduces the degree of difference between the colors. There is also a timer that adds a level of stress when it starts beeping at you.


Try to view the grid as a whole rather than scan them, looking for the different color. It's much easier when you're being timed to look at the big picture.

Here's how dogs actually see the world

How do dogs see the world? Dogs see differently than humans.

The reason lies within the eye. In the eye are light receptors called cones and rods. Cones help us distinguish different colors, while rods help us see in dim light.

The number of cones and rods is different for dogs.

Turns out, dogs have fewer cone receptors than humans — which means they can't see as many colors. Human cones can detect 3 colors: red, green, and blue.

Dog cones can only detect 2 colors. No one is certain what those 2 colors are. Some experts think it could be blue and yellow.

Alexandra Horowitz — author of "Being a Dog" — told us that it's difficult to know exactly what colors a dog sees, but it's probably similar to what we see at dusk.

Dog eyes have more rods than humans, which means they can see much better at night. Dogs also have a layer of eye tissue that humans lack called the tapetum lucidum, it reflects light into the retina.

This boosts dogs' night vision even more and is why dogs' eyes shine in the dark. Turns out, dogs' eyes see much more than just black and white.

The eyes look, but the brain sees

Certain objects attract our attention in a particular way. It could be something that is especially ugly or something that we perceive as being rather pretty.

With a background in design, I ought to know something about what makes one object appear prettier than another. However, you don&rsquot have to look far before it becomes difficult to predict whether something is likely to be perceived as ugly or nice.

So, what is it that catches and keeps our eye fixed to something &ldquonice&rdquo?

It&rsquos often said that the human eye is developed for life on the savannah, and it is particularly sensitive to detecting movement in our periphery. This peripheral view helped us to survive by allowing us to react quickly to danger approaching from either side.

However, our peripheral vision is not particularly sharp. We can only see clearly, when we look straight ahead, we cannot read in the peripheral field of view, and worse still, we cannot see in colour&mdashwe only see colour in our central vision.

So, your full colour, HD-resolution image of the world does not come from your eyes, but your brain.

The brain selects information

The brain translates the information it receives from the eye into something that we can understand. In fact, the brain receives just three &lsquoimages&rsquo every second, which are sorted and combined with earlier information to create the reality that you experience.

This is happening all the time while your eyes are open, and it requires a certain amount of energy. To avoid overheating, the brain saves energy by choosing what is worth looking at.

But how does the brain choose what to observe and ignore?

Two types of vision

Roughly speaking, we have two systems of vision. One system prevents us from bumping into things and enables us to move around. It&rsquos called &lsquoorientation attention&rsquo, and it operates quickly, saving energy, as the brain is not required to develop a full understanding of your surroundings.

The other system is called &lsquodiscover attention&rsquo. This operates more slowly, as the brain collects information from our memory to obtain a full understanding of the scene.

An example of the two systems in operation can be seen when you walk down the street. The orientation system allows you to easily move in and out of the path of other people, and stops you from falling over or walking into a lamppost. But when your eye catches sight of something interesting in a shop window, you switch over to the discover system to get the full picture.

The object you&rsquore looking at might seem familiar, but has a different shape or colour. How long you spend looking at the object, depends on how much sense it makes to you and the number of other things you&rsquore thinking about at that time.

How to fix your attention

We use these two systems alternatively without even realising it. Since the orientation system requires less energy, we quickly switch back to it when we have enough information.

In reality, we know that objects with certain characteristics are better at catching our attention, while others are better at holding our attention.

By measuring eye movement, we can see that the orientation attention is influenced by the object&rsquos shape and contrast. My research shows that we are more likely to notice certain products, which use these basic design parameters to stand out.

To keep our attention the brain needs to decide that it is worth using energy to understand this new object. And research shows that we keep our attention on things that are easier to understand.

If it becomes too demanding, or nothing else is happening, our attention slips, and we begin to look at something else. Perhaps you&rsquore experiencing this right now! Is it worth the effort to continue?

If you&rsquore still with me, then here comes another explanation: You might expect this article to be interesting because it&rsquos published at ScienceNordic. In visiting this site, you already made up your mind that you would find something interesting to read.

Also of significance is the amount of information you receive. Research shows that the number of elements that we can see directly influences whether we continue to look or shift our gaze elsewhere.

When there are too many things to look at, the brain needs to work harder, and there is a higher risk that we will stop paying attention. Our brain is simply not good at multitasking.

The brain adapts quickly

It is quite impressive that a brain designed for a life thousands of years ago copes as well as it does in the modern world. This is due to our ability to adapt. In fact, it takes the brain less than a minute to adapt to new surroundings.

You can try this yourself: Try looking at this image above of a moving spiral for 30 seconds, and then look away.

You&rsquoll notice that your visual world is now transformed by your brain, and that stationary objects seem to bulge and move. But then see just how quickly your brain switches back to a world where those objects are once again stationary.

When I research the workings of the eye and the brain at Copenhagen Business School (CBS), which you might not associate with this type of research, it is because it helps us to understand how we as consumers make choices. And studying the visual system, gives valuable insights into why consumers sometimes make irrational choices.

Over many years of research at CBS, I have conducted experiments and tests to find out what captures and holds our attention. My research ranges from questions of what we perceive as being ugly or pretty, to what prompts us to sometimes buy a cat in a hat.

How Do We See Colour?

How many different colours can you name off the top of your head? Ten? Twenty? Fifty? I bet that no matter how many colours you listed, it’s not even close to the number of colours your eyes can see.

Misconception Alert

Seeing and perceiving do not mean the same thing. Seeing is the process that your eyes use to collect information and send it to your brain. Perceiving is how your brain takes that information and makes sense of it.

Scientists estimate that the average human can distinguish over a million different colours. But that is not true for everyone. Some people can only see a few hundred different colours. Others can see up to 100 million!
Why is this? What exactly is colour? And how do we see it?

What Is Colour?

When light hits an object, the object reflects some of that light and absorbs the rest of it. Some objects reflect more of a certain wavelength of light than others. That’s why you see a certain colour. For example, a lemon reflects mainly yellow light. A strawberry reflects mainly red light.

Objects that absorb all wavelengths of light appear black. Objects that reflect all wavelengths of light appear white.

What happens when light hits a transparent object, like water or glass? When light travels from one medium to another, the light is not reflected like it would be on a solid object. Instead, it bends. That’s because light travels at different speeds in different mediums. This is called refraction.

When light travels through a glass prism at an angle, the different wavelengths of light are slowed down by different degrees so that each colour has a different angle of refraction. As a result, you can see all of the colours contained in white light.

But the reflection and refraction of light on an object is just one part of the story. Let’s look at what happens in our eyes and brains when we see colour.

How Do We See Colour?

A layer called the retina sits at the back of the human eye. Your retinas are home to two types of photoreceptor cells: rods and cones. These specialized cells convert light into signals that are sent to the brain. This allows you to see.

You have 20 times more rods than cones. Rods allow you to see in low light. Cones are 100% responsible for colour vision. Have you ever noticed how hard it is to see colour in the dark? That’s because only the rods work in low light.

There are three types of cones: red, green and blue. Each type respond to different wavelengths of light. Long wavelengths stimulate red cones. Short wavelengths stimulate blue cones. Medium wavelengths stimulate green cones. When different combinations of cones are activated, you see the world in colour.

What Is Colour Blindness?

Colour vision deficiency, often called colour blindness, occurs when one type of cone is completely missing from the retina or simply doesn’t work.

As you just learned, there are three types of cones. That means there are also three types of colour blindness. The type depends on which type of cone that is missing or not working.

The loss of red cones is called protanopia. The loss of green cones is called deuteranopia. We usually refer to both of these conditions as “red-green” colour blindness. They make it very difficult to distinguish between shades of red, yellow, orange and green. This is the most common type of colour blindness.

Did you know?

The genes that make cones are on the X chromosome. This explains why 8% of men have red-green colour blindness, while less than 1% of women do.

A person with protanopia is less sensitive to red light. Remember that rainbow you saw earlier on? A person with protanopia might see it as yellows and blues, like this:

People with deuteranopia are less sensitive to green light. They’ll also see the rainbow as yellows and blues. However, the colours will be different. A person with deuteranopia might see the rainbow like this:

Tritanopia is a form of colour blindness where a person can’t distinguish between yellows and blues. It’s also called “blue-yellow” colour blindness. It’s a very rare condition that results from the loss of blue cones. People with this condition have difficulty distinguishing blue from green and yellow from purple. A person with tritanopia might see the rainbow as shades of red, pink and green.

Another rare form of colour blindness is called achromatopsia.

Incomplete achromatopsia involves the loss of two out of the three cone types. Since the brain needs to compare signals from at least two different cones to properly identify colours, people with this condition have severely limited colour vision.

Complete achromatopsia is the loss of all three cone types. People with complete achromatopsia see the world entirely in shades of grey.

Did you know?

People with typical vision are called trichromats. That’s because their eyes have three types of functional cone cells. People with only two functioning types of cones are called dichromats.

What Causes Colour Blindness?

Most types of colour blindness are the result of genetic mutations. Some mutations cause cone cells to only partially work. This leads to a milder form of colour blindness. Other mutations cause missing cones cells. Colour blindness can also be the result of brain damage, chronic illness or taking certain medications.

Did you know?

Many mammals, including nocturnal mammals, marine mammals and most New World monkeys, are dichromatic.

Can Some People See Even More Colours?

On the other end of the spectrum, researchers recently discovered that up to 12% of women may actually have four types of cones in their retinas! This is called tetrachromacy. A person with tetrachromacy is called a tetrachromat. Scientists have suggested that these women may be capable of seeing up to 100 million different colours! This includes colours that the average person can’t even imagine!

Did you know?

The prize for superior colour vision has to go to an animal called the mantis shrimp. It has sixteen different types of photoreceptors!


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