A Brief Overview of Colour Perception and Colour-blindness

What is colour?

To begin, I think it’s important to realise that colour as we know it does not exist in the objective world.  Wavelengths do. Lights of different wavelengths form an additive colour mixture, and the composite of all the wavelengths form white light. Paint on the other hand, have a subtractive nature and absorb all wavelengths except the one you perceive it as. The subtractive mixture of all paint, as any toddler could probably tell you, is black.

Figure 1: Visible light spectrum in terms of wavelength.

As children we learn the “VIBGYOR” (or ROYGBIV) method to memorize the colours of the rainbow. This represents the spectral colours. You can also turn the spectrum into a colour wheel, as it was first described by Newton in 1708.

Figure 2: Farbentafel (Color wheel). 1874. by Wilhelm von Bezold.

Modern colour psychologists also add purple and reddish-purple in between red and violet, although these are not on the visible spectrum.

Now we know that the wavelength of light determines what colour it appears to be. Other characteristics of colour is it’s saturation, which can be thought of as a spectrum of grey to the colour; and the intensity or brightness, which can be thought of as a spectrum from black to white, with the colours in between. Given these other dimensions, the best way to represent all possible visible colours is the colour spindle as shown below.

Figure 3: Colour spindle. The circle represents the hues previously shown in the colour circle with brightness on the y-axis and intensity shown radially from the centre of the circle to the outside.

Let’s for a moment, go back to just the primary colours, i.e., the wavelengths which mixed together in different proportions can produce any other colour on the wheel. Red, blue and green define the colour triangle. The problem with this version is that some colours are not additive of two other colours on the triangle. Yellow, for example is a negative primary, i.e., you have to subtract one primary from another (green from blue). To overcome this problem, the Commission Internationale de l’Eclairage (1931) was charged with creating an imaginary colour triangle that was defined by proportions of red and green, and added a dimension for brightness.

Figure 4: Primary colour triangle (Maxwell, 1860)

Figure 5: Imaginary colour triangle (Commission Internationale de l’Eclairage, 1931).

Colour perception

How do we see colours if they don’t exist in the objective world? That my friend, is an excellent question, and presumably why you came upon this post in the first place. Colour opponent theory suggests that a particular neuron is activated by the presence of one colour in the centre and/or the present of another in the surround area of the cell. So for example a red-green colour-opponent neuron would be activated by medium wavelengths in the centre and deactivated by longer wavelengths in the surround cell area. Colour-opponent cells are found in blobs in layer 2 and 3 of V1. Cells in V1 layer 4 and V4 have double colour-opponent cells, i.e., it is activated by the presence of a particular wavelength in the centre and the absence of it in the surround, but also activated by the presence of it in the surround and absence of it in the centre. A classic example of this is the red-green double colour opponent cells, also known as “berry on a green leaf detector”. Here’s some diagram examples to help visualise this concept. (-) indicates an inhibitory effect and (+) indicates and excitatory effect.

Figure 6: Color opponent and double opponent cells. The double opponent cell represents the “berry on a green leaf” detector. (From http://www-psych.stanford.edu/)

Colour blindness

Once upon a time, long, long before my advent into psychology and neuroscience, I had a friend who is colour-blind and like a true scientist in the making, I spent hours asking him about what colour different objects appeared to his vision. Before that point, I thought that people with colour-blindness literally could not see any colour and instead saw the world as a black and white movie from the 20’s (but with better resolution). Turns out this form of colour-blindness is extremely rare. For someone to completely lack all colour vision, they would have to lack cones. I suppose before I go into this, I should go over rods and cones a bit.

Rods contain rhodopsin, which is “bleached” in the presence of light. As a result, they only really work in dim light condition and is necessary for night vision. Rods mostly reflect 500-550 nm wavelengths.

There are three types of cones, each of which help us see a different primary colour. They are aptly called red-cone, green-cone and blue-cones.

Figure 7: Rods and three types of cones help us see different wavelengths of light.

Going back to my juvenile misconceptions about colour-blindness, a complete lack of colour vision is extremely rare (1 per 100,000 people) and would require a complete absence of all types of cones. They are called rod monochromats and since rods don’t function well in bright light, by and large, they are legally blind. Blue-cone monochromats are less rare.

People with only two types of cones are called dichromats. Red/green colour-blindness is the most common of all, in part because there are two types of dichromacy that causes this. Protanopia is caused by long wavelength cone deficiency, and deuteranopia is caused by medium cone deficiency. In both cases, people see in hues of blue and yellow. A third, very rare type called tritanopia is caused by a short wavelength cone deficiency, causing blue/yellow impairment and seeing mostly turquoise and red (lacking the solid blue/violet end of the spectrum).

Figure 8: Trichromacy vs. the three types of dichromacy.

The last type we will briefly mention are anomalous trichromats who have all three cones but one type is abnormal and discriminate hues poorly. I don’t have any simulation examples for this, since the results would be variable depending on which type of cone malfunctions and how.

I hope this has been very informative, and that you will use this as a handy resource. And the next time someone says they are colour-blind, you will refrain from quizzing them endlessly about what colour objects are. Or go ahead and do it; that’s how I started after all! Of course, hypothetically, we all see slightly different colours as red, or green or purple…no one has exactly the same number of cones and all of them do not function exactly the same!

IQ tests: A history and current uses and issues

I have often been known to say that I don’t put much stock in IQ tests, to those who know me well. Certainly, it does not mean that IQ tests don’t matter, or don’t tell us anything. It simply means that the layperson often use it today to mean something very different than what it was originally intended to mean. As well, a lot of pop “IQ” quizzes have come up, thanks to the internet, adding to the confusion. So in this post, I will go over the history of IQ tests a little bit and talk about the current issues surrounding IQ tests.

(Note that a lot of the information in this comes from my lectures and class notes, so I am in the continuous process of finding primary sources for the information. Please be patient.)


At the end of the 19th century, a new law in France mandated that all children aged 6 to 14 must attend school. To accomplish this, it was necessary to devise a way to help children with learning disabilities so they might progress through the ranks instead of being stuck in the same class while their peers move on. Alfred Binet, along with his student Theodore Simon devised a test for this purpose called the Binet-Simon test which was published first in 1905. Subsequent revisions were made by Binet in 1908 and 1911, before he died.

The test was created by averaging the performance of students on several measures in several classrooms, and the results were cross-checked by conferring with the teachers. In other words, if Sally is considered by all of her teachers to be very smart and doing well in all of her classes, and she did very poorly on a measure of intelligence, it was considered to be useless in serving the purpose of the Binet-Simon test. The test measured performance of an individual student compared to the average of that age group. The purpose was to isolate those who were performing far under the average and put them in special classes where they can get extra help.

The Binet-Simon test was soon imported over to the United States of America, where it quickly gained popularity, albeit due to historically condemnable reasons. The Binet-Simon test was picked up by H.H. Goddard, a champion of the eugenics movement and used to prove the “superiority” of the Whites. It was used to curtail immigration of Jewish population to US during WWII on the basis of “lower intelligence”. This is the opposite of what Binet himself believed, i.e., that intelligence was a qualitative rather than quantitative characteristic, and was malleable and depended on the environment, and not solely dependent on genetics. He also stressed that IQ scores could only be compared amongst children with comparable backgrounds. I will elaborate on this more on the section about issues.

David Wechsler first published his test in 1939 and by the 1960’s, the popularity of his test overtook that of Binet’s. It has undergone several revisions by now and the WAIS IV and the WISC V are considered the gold standard in psychometric testing for intelligence.

Current measures of intelligence

The Wechsler Adult Intelligence Scale (WAIS IV) and Wechsler Intelligence Scale for Children (WISC V) have various sections with items that measure different kinds of intelligence. The sub-tests look at verbal comprehension, perceptual reasoning, working memory and processing speed. The tests have been standardized on large samples from both the USA and Canada, and people are scored against the “norm” (the normative range) of their own country. This does differ, as the average score of the Canadian sample is much higher than the US sample. There also exists a French version of the test. The administering of the WAIS and WISC are strictly regulated and a clinical psychologist who intends to administer it undergoes rigorous training before they are allowed to do it independently on actual clients.

IQ scores are often reported as a range, as opposed to a specific number. However, most IQ tests that have been rigorously standardized (so, not that 5 minute Facebook quiz you took 2 years ago) have been shown to be reliable. IQ is stable over time, given that you don’t suffer a traumatic head injury or infection, or one of the many things that could possibly affect your brain tissue. There’s quite a few of these neurodegenerative diseases and this is actually one of my main interests.


Given that IQ tests are based on normative scores in a population, it is important to stress that it’s really useful for identifying people at either ends of the spectrum. The average IQ is set at 100-110 points, above 130 is considered well above the average, below 70 is considered an intellectual disability. There are levels to this as well, eg., below 20 is severe intellectual disability and a case where the person would be completely unable to survive on their own and usually need a live-in caretaker. IQ scores are not really all that useful for distinguishing between people who fall within the normative range of intelligence.

There is some debate amongst psychologists on the issue of how to report and interpret the data. Some have questioned the utility of reporting it as a raw score (eg. a score of 122), as opposed to a percentile score (eg., Jane Doe scored in the 75th percentile, meaning they did better on the test than 75% of the population) to really drive home the point that the results are on a relative rather than absolute scale.

The average IQ changes over generations, and it is on an upwards trajectory. Criminals with an IQ of less than 70 are considered to be intellectually disabled and put in re-mediation programs rather than prisons. The debate surrounding this is that there might be criminals who were put in prison back in the 70’s or 80’s because they were above the cutoff at the time of their conviction, but would be below 70 and considered intellectually disabled now.

The IQ tests were initially based on a population that is very specific. The subjects measured were all white, middle-class males who were in the education system. As a result, there is some queries about the validity of IQ tests to measure intelligence in populations who fall outside of these parameters. There are issues with cultural interpretation of questions. Certain questions are simply not relevant to certain cultural lifestyles and therefore they would not be able to answer those questions. For example, suppose a question asks you the velocity of a bicycle going downhill at an inclination of 24° and an initial height of 38 meters. If you are from a remote island where bicycles are not a common means of transport and you have never seen or experienced riding a bicycle, you are not going to be able to answer the question. Rather, your question would be, “what is a bicycle?” That does not mean that cultures without experience with the items in a given IQ tests are not intelligent, or below a functioning level of intelligence. To administer the WAIS, you have to be fluent in the language, as does the client.

This is by no means a comprehensive list of all the issues, but it outlines some of the main points. That’s all, folks! If there are specific questions about IQ tests or the concept of IQ in general, feel free to comment and I will answer to the best of my ability.

Suicide prevention

In Canada, 10% of men and 13% of women in the general population has contemplated suicide at some point, and 2% of men and 6% of women attempted it. The highest risk is for late adolescents and emerging adults (15-24 year olds).

Depression and suicidal thoughts are surprisingly common, but not everyone who is depressed are suicidal. So how do you assess risk?

  • Talking about it is a start. 80% of people who attempt suicide talked about it before doing it. Unfortunately, they are not always taken seriously. In case of adolescents, parents might not take it seriously enough to get their teen help, or start and then terminate treatment prematurely. People do often callously say “ugh, kill me!” and the like, at the slightest inconvenience, but people having suicidal thoughts will probably show other signs.
  • You could just ask them straight up if they feel like they might want to commit suicide. Sometimes, they will just tell you, “You know what, yes I am.” And then you can move onto trying to help them.
  • Hopelessness is a strong sign. If they are constantly making self-defeating statements, and talking about failures like it’s stable (a permanent fixture of their life) and global (encompasses all aspects of their life, e.g., “I got a D in a course, I’m a terrible person who will never succeed”), there’s cause for concern. Hopelessness is a strong motivator for suicide.
  • Planning. Try to ascertain how much planning has gone into this. Did they buy a gun? Do they have an inordinate amount of sleeping pills in the medicine cupboard? Have they been composing a suicide note? Planning can also take the form of getting their affairs in order. They might be writing a will, selling or giving away their possessions, paying off debts and bills.
  • Impulsiveness. Is it possible that they might act completely ok right now and then an hour later go to the pharmacy by some pills and swallow them right away?
  • Do they have access to the things they need to commit suicide? Blades, pills, guns?
  • Do they have a support system that might prevent them from actually committing the act? This could be family or close friends, even a pet. One of my profs told us a story about how this one guy had the access, planning, everything in place but couldn’t do it because he did not want to leave his dog behind. I personally knew someone who had similar thoughts but decided not to because it would hurt his parents.

What can you do to help? While I’m writing this part I’m going to assume you are not a clinical psychologist or a psychiatrist because they have different protocols they have to follow with their clients. And I know very little about that.

  • You can stay with them and ask why they feel that way. Often people feel trapped and don’t see a lot of options. They see death as a permanent solution to, what seems to them like a permanent problem. So maybe you can help them find a different way of dealing with whatever problem their having.
  • You could ask them if they wanted help. If the answer is even close to a maybe offer to walk them to the closest mental health center. This assumes you live near somewhere that has an MHC. Try to get them help right away, because they might say, “Oh yeah, you go home, I’ll give them a call.” But it’s most likely they will not. They may want help but lack the motivation to do anything about it.
  • Ultimately, if they do not want help, you can’t force them to get it. You can’t chain them to the dishwasher while you send for help. If someone is adamant that they want to end it all, you can’t really stop them. But you can do one of the following:
  • Alert someone close to them, their family, or their roommate, someone who lives with them so they can keep a close eye on them. If they live alone, alert a family member anyway.
  • If you think they are in immediate danger, as in, they’re going to walk out of here and through themselves in from of a semi, you can call for help, call the police and ask them to help you drive the person to the hospital. They need psychiatric help and to be somewhere where they can be observed while help is provided.
  • Don’t talk down to them o their situation, don’t say things like, “You’re talking crazy.” It’s very diminishing and de-legitimizing and it doesn’t actually help.

Since this is a very important post, I will keep this filed away under the “Resources” tab.

Welcome to the (neuronal) jungle.

A man and his young son were apprehended in a robbery. The father was shot during the struggle and the son, in handcuffs was rushed to the police station.

As the police pulled the struggling boy into the station, the mayor, who had been called to the scene, looked up and said “My God, it’s my son!”

The story stared back at an entire roomful of intelligent, mostly second year university students. Continue reading