Colour on the Brain - part 1

How do we see in colour? What actually is colour anyway?
20 February 2020
Presented by Katie Haylor
Production by Katie Haylor.


Paintbrushes dipped in yellow and red


Be it burnt orange, millenial pink, inky black, dusky, deep purple, colour is everywhere! Over the February and March 2020 episodes of Naked Neuroscience, we’re opening up the paint box of colour. In this episode Katie Haylor will be putting her retinas to the test at the optometrists, and finding out about how we actually see colour in the first place. Plus, some neuroscience news from our local experts...

In this episode


01:14 - Why do we love a thriller?

Join local neuroscience experts Helen and Duncan as we tuck into some Naked Neuroscience news...

Why do we love a thriller?
Dr Helen Keyes, Anglia Ruskin University; Dr Duncan Astle, Cambridge University

The paper perceptual psychologist Helen Keyes has been looking at this month has found that we enjoy stories of revenge more than stories of forgiveness. Perhaps not surprising, as many of us enjoy a thriller. And this paper sheds a little light on why that might be...

Helen - When we engage with a fictional piece of work, we can approach it from an enjoyment perspective or from an appreciation perspective. And we know from our own viewing experiences that this isn't always the same thing. So for example, you might really enjoy watching repeats of Friends or watching some Love Island, but from an appreciation perspective, when you really want to have some deep meaningful connection with a narrative, you might watch a historical documentary or an arthouse movie. So we know that these are different ways to appreciate some art. These two approaches satisfy different needs that we have. So the enjoyment approach can satisfy some emotional needs, a really lower order drive to get that satisfaction from a narrative. So from an appreciation perspective that satisfies a different need, a more cognitive need, a more higher order need.

And the authors were interested in looking at retribution here. And that's because there is a lot of work done around something called the Just World hypothesis, which is an intrinsic need that we have to believe that the world is just, this is a real motivator for our behaviours. If we didn't believe the world was just, it would be hard for us to keep going and thinking, "if I put this hard work in, there's a reward for me there at the end". And "if I don't, if I transgress this boundary, there is going to be a punishment for me here". We're all invested in this idea that the world is just and therefore we have a desire to see justice done. And so these authors asked 206 students to read a number of scenarios, and these scenarios either had a narrative of under-retribution, equitable retribution, or over-retribution. You're presented with a story where a coworker has stolen 50 pounds, an under-retribution narrative would be that you then go and buy them a coffee. An equitable retribution narrative would be, you go and steal a 50 pound bottle of whiskey back from their office. And over-retribution, you would go and steal the 50 pound bottle of whiskey and also download a virus onto your coworker's computer.

Now the participants had to press a button as to whether they liked or disliked this narrative on a really basic level. And the authors also measured how quickly they press that button. But following each narrative, they also asked participants how much they enjoyed the narrative. So questions about whether it was a fun story, whether it was an entertaining story, and they asked questions about the appreciation of the narrative. So, "Was this a thought provoking, or moving, or meaningful narrative?" And what they found was people liked the equitable retribution stories the most. And this fits in what we know about a Just World hypothesis. People liked it when somebody steals 50 pounds from you, so you still 50 pounds back. That was liked the most and it was also responded to the most quickly out of all the options, suggesting it was a real intrinsic, gut-level decision, "I like this. This is fair". However, when it came to enjoyment, participants enjoyed the over-retribution scenarios significantly more than any of the other scenarios. And on the flip side of that, they appreciated the under retribution or the forgiveness narratives more than the other types of narrative.

So it suggests that, while we know what's fair and we like what's fair, when it comes to entertainment and enjoying something, we like to indulge that revenge fantasy. But if we want to have a meaningful deeper connection with something, we appreciate that deeper, slower to respond to, more thought-provoking forgiveness approach.

Katie - I feel like that makes sense, right? Because when you're talking about fiction, you're in a safe space where you can go over the top in terms of retribution.

Helen - It certainly explains the number of revenge plots in movies and books, whereas in real life, revenge plots aren't really that common. We don't usually build our lives around seeking revenge. It links in nicely with a lot of research around watching horror movies and the experience of fear or the indulging of these heightened intense emotions. Like you say, we like to do that in a safe space. So you're watching this revenge narrative and even though you know it's not fair and it's not something you'd like to see in real life, it feels nice to indulge in that heightened emotion, in this safe controlled environment, in the same way we might enjoy feeling scared.

And there's a lot to be said around the transfer of excitation here as well. So this is when you watch something that makes you scared or feel excited and that feeling, that arousal, the increased heart rate and those responses can transfer over to more positive experiences later. So if you're hanging out with your friends later, that increased arousal can really transfer into a positive experience for you.

Katie - Duncan?

Duncan - I was wondering how culturally specific this might be. Does everybody regard the same thing is just or unjust? I can imagine there are cultures or societies in the world where what they see as justice actually is sort of much harsher.

Helen - Yeah. And I think what is quite intrinsic and natural to people is the desire to see justice. But you're absolutely right. What people view as being just is very culturally dependent. And the large body of research on the Just World hypothesis explores this in great depth, what you believe to be justice is very culturally dependent. But what doesn't change is that people's drive to see whatever it is they see as just is very constant across people.

The paper Cambridge University cognitive neuroscientist Duncan has been looking at this month delves into the teenage brain...

Duncan - So traditionally about 20 or 30 years ago, we believed that brain development in humans finished at the end of childhood. So when someone's 10 or 11 years old. But we now know that actually the brain continues to develop and change throughout adolescence, which is defined as a period between puberty and adult independence, which is typically thought to be about mid twenties.... I thought you were going to ask me a question there but you're not!

Katie - No, I'm going to keep my age out of this interview!

Duncan - And so now we know that the brain continues to develop over that period of time, there are some really interesting questions to ask. So how does it continue to change, and why? And how do those changes relate to changing behaviour? So we know that as people transition from being children to adolescents, and then to adults, there are big changes in their behaviours. So for instance, the propensity for risk taking changes a lot. And how's that related to changes in the brain?

Katie - How did they seek to look into this, then? What did they do?

Duncan - So they gathered data from 298 individuals, who are aged between 14 and 26, and each person is seen multiple times, so it's a longitudinal study. And what they did for each time they saw a subject is that they would scan their brains using functional magnetic resonance imaging. And what this is able to do is track fluctuations in brain activity in multiple different regions at once. And so with these scans, across multiple different time points, at different ages, they were able to measure how well different brain areas are connected with each other. So for example, if you have two brain areas and the activity of those two areas fluctuates together, even though they're anatomically separate from each other, that implies those two brain regions are functionally connected to each other.

So you can imagine if we had scans for each person at multiple points in time, we could then chart the changes in how different brain areas are connected to each other, as the person is getting older. And this is what they did, and they found that there were multiple different changes in connectivity and they could group those changes into two classes. The first class was a set of brain regions where areas that are strongly connected just become more strongly connected. A bit like the rich become richer. And those areas are involved in things like motor control, vision, listening skills. But they can be distinguished from a second class of brain regions, areas that are well connected become less well-connected, and areas that are not well-connected become more strongly connected over time, as if what's actually happening is that there's a reorganisation in how these brain areas are connected.

Now interestingly, the second class of brain regions we know to be involved in higher order thinking skills, things like memory for your personal events, social skills and social cognition. And so what the authors are able to show is that there are these two separate types of brain development that are going on during adolescence; some areas that just become more embedded or the established connections just become stronger, and other areas where there's a massive reorganisation in which areas are connected to which areas. And this seems to mirror or match on to differences in cognitive skills.

Katie - Was there much variation between people? I'm wondering if the bits of the brain that you're talking about develop at different rates depending on the individual.

Duncan - Yeah, there's massive variability. So the headlines that you'll get in a paper like this describe the group average results. But if you dig down and look at the figures, you'll see that there are individual data points corresponding to individual participants, and that gives you a real window onto the variability. So there's a massive variability and that's why whenever we describe when adolescence starts and ends, it's group average. So for some people we would characterise their adolescence of having ended much later and others much earlier.

Katie - How significant would you say this result is?

Duncan - I think this characterisation of there being two types of brain development over this period of time is really, really interesting, because you can imagine that the genetic underpinnings of these different types of development could be different, and that might provide a really important window on the genetic underpinnings of differences in, say, social cognition or the susceptibility for different types of mental health difficulty that we know have an onset during adolescence. So I think that's really interesting.

But there are also lots of unanswered questions. So for example, it could be that all brain regions go through this disruptive phase and then this conservative phase, and that actually what the authors have captured here is that areas involved in social cognition and areas in the frontal cortex and the parietal cortex just mature much more slowly. And so you're capturing their disruptive phase before they get to their conservative phase. Whereas areas in like the motor cortex or in vision, they've already been through their disruptive phase, it happens much younger, and now they're in their conservative phase, which is a little bit different from the way the authors describe it.


How do we see in colour?
Professor Anya Hurlbert, Newcastle University

From the clothes on your back, to the natural environment, vehicles, buildings - you name it, colour is all around us! So how do we actually see colour? Katie Haylor asked Anya Hurlbert - medic, physicist, and professor of visual neuroscience at Newcastle University...

Anya - I do find colour very exciting to me personally, but I also find it a very rich area for exploring how the human mind and brain work. Because all of those different disciplines feed into the study of colour, from the physics of light, to the genetics of light reception in the eye, to the physiology of the way the neurons work at the different levels of the brain, all the way up to cognition, how we label colours, how we name them, and then how they relate to our emotions and how we use them in daily life.

Katie - So we're going to tread that path. Can we start off with a very brief rundown of the basics? I'm currently looking at a computer screen with a very bright blue background. How am I perceiving that as blue?

Anya - Your photo receptors in your eye are picking up that light signal and analysing it in terms of its different wavelength components in a sort of bluish band, a greenish band and a reddish band. The cells further on in the visual pathway are comparing how much bluish, greenish, reddish light there is from your computer screen relative to the background. So when you're seeing colour, you're always seeing relative light amounts from the thing you're looking at, relative to the background.

Katie - So that means that the quality of the colour is dependent upon the light source, right?

Anya - Absolutely. And since you were talking about your computer screen, I was sort of thinking of your computer screen as the light source. But of course, most things we look at are not light sources, they're surfaces. They absorb light incident on them from a light source and then they reflect the remaining light to the eye. So what we're seeing when we see colours of objects, is the intrinsic material properties of the object that enabled them to reflect certain wavelengths more than others. But the light that hits the eye is a combination of the light that's shining on it from the light source and the inherent reflectance properties of the object.

Katie - Does that mean that if we're looking at something under natural light compared to artificial light, there's quite a difference in what we're actually perceiving in terms of colour?

Anya - Well, there's a huge difference in terms of the light that's hitting the eye. If I take an apple and I look at it in bluish sunlight, it will be reflecting much more bluish light to my than it does when I take it inside and look at it under say tungsten light, or candle light, which has much more orange light in it. So that red apple would reflect more of that orange light to my eye. But what my whole visual system is doing, from eye to higher levels of the brain, is sort of filtering out that difference in the light shining on the apple. So that I can continue to see it as red.

Katie - Thing is, if we step outside and light sources aren't constant, you might have clouds in the way or other variations. So how does something that I perceive as red keep staying red?

Anya - Well, that whole phenomenon of seeing that apple as red under, as you say, hugely varying lighting conditions is due to this phenomenon that we call colour constancy. And it's deeply embedded in the way we see colours and it's deeply embedded in our whole visual system, in human vision. We're constantly accommodating and compensating for these changes in the light shining on objects.

Katie - So what's the brain doing in order to achieve that?

Anya - It's thought to be doing many different things on multiple levels, from simply adjusting the sensitivity of the light receptors in the eye initially, so that if all the light in the room suddenly goes very reddish, the so-called red cones in the eye will adjust their sensitivity down to compensate for that change in the illumination, to keep the light coming off objects relatively stable. Or to keep the light signals in response to the light coming off objects relatively stable. If there's more red light coming off them, but it's due to the illumination, you want to turn down your sensitivity to that and that's what the receptors in the eye do.

But it's not just in the eye, the brain is continually assessing and adjusting to these changes in the illumination. That can include levels of, for example, memory. So the fact that I have a memory colour for a banana as being yellow might help me to adjust to changes in the colour of the illumination because I can compare the light reflected from the banana at this moment in time with what I know it's colour should be, based on my memory colour. And then calibrate for those changes in the illumination accordingly.

Katie - That's incredible. I imagine that's not conscious, right? That's going on below the surface!

Anya - Yes, it's completely unconscious. We're totally unaware of that. What our brains are doing is really, really phenomenal in day to day, millisecond to millisecond vision. And colour constancy is one of those fascinating phenomena that is really very, very complicated, and we know it's a really massive achievement of the human brain because it's so difficult to enable cameras to achieve the same thing.


20:33 - Testing colour vision

What does a colour vision test involve?

Testing colour vision
Sonam Ruparelia, Anglia Ruskin University

Optometrist and colour vision PhD student Sonam Ruparelia from Anglia Ruskin University’s eye clinic put Katie Haylor's cones under the metaphorical microscope with a colour vision test...

Sonam - We're in our colour vision lab actually in the eye clinic, so we carry out a range of colour vision tests in here. Particularly useful for those who want to get occupational colour vision screening checks done and if someone has been identified to have a colour vision deficiency, then we can test for the extent of it here as well.

Katie - Turns out not everyone actually has red, green and blue cones.

Sonam - And that's where we tend to have more severe colour vision deficiencies. So some people have two and others can only detect greyscale vision. For those who do have two cone cells, they can detect still a range of colours, but it tends to be varied compared to someone with normal colour vision. There is definitely a higher prevalence in male across the board from the studies that have been carried out. Colour vision deficiency is a recessive condition because males have an X chromosome and a Y chromosome. If that congenital deficiency is lying on the X chromosome, they are likely to have the condition. With females because they have two X chromosomes, there is the possibility that because it's a recessive condition, they may be able to get away with not having anything, if that chromosome doesn't fall on both Xs.

Katie - How are you going to test my vision?

Sonam - So if you went for an eye test at an opticians, chances are they may carry out an Ishihara test. So that's what we'll be using today. And what that test involves is looking at numbers of a specific colour on a different coloured background.

Katie - Okay. She says slightly nervously. Let's do it.

Sonam - Okay. So what we're going to use is an Ishihara book, and we're going to have good lighting, and we're going to take a look at the pages and see what we can see. If I show you the first page, take a look at that and just tell me what number you can see.

Katie - It looks like an orange 12 on a bluey greeny bubble background.

Sonam - Excellent. So this one is particularly good when we're testing children as well because this is what we call a demonstration plate. We expect everyone to be able to see this regardless of whether they have normal colour vision or not.

Katie - Okay. So you're just testing me.

Sonam - That's right. Yes. Particularly good for children. Um, especially if they want to be wearing spectacles. They like saying all sorts.

Katie - I see. Wow. So you're a fib detector as well as an optician!

Sonam - We try! What number can you see on there?

Katie - It looks like to me an eight, pink and orange on a bubbly green background.

Sonam - Perfect. And then we move on to the next page.

Katie - Same colours. Looks like a 29.

Sonam - Very good. So someone with abnormal colour vision may see a different number on this background compared to what someone with normal colour vision would see.

Sonam - Has that got anything to do with the more bluey bubbles I can see around the 2 and around the 9?

Sonam - That's right, yes. So they would be unable to see that red very well. They would detect that green a little bit more. So if you wanted to look at that one.

Katie - So this to me looks like a 5 in a bluey green hue on an orange bubble background and then the page next to it, I think a 3 in the same colour tones.

Sonam - Excellent. Yes, that's exactly what it is. And if we were to carry on through those, particularly for very young children who struggle with this kind of test, we do have similar combinations but with patterns for them to trace instead. And likewise, if I show you this one here: so if I told you that there was a squiggle on this background, this multitude background of colours, would you be able to agree with me?

Katie - Honestly, I'm finding it really difficult. I don't think there's a pattern there. I can't see anything.

Sonam - So someone with abnormal colour vision would be able to see something here. It's not just designed to catch you out with everything you find difficult. The idea is also to be able to see things as well because there's always a motivation factor in being able to see something. So these are slightly different again, so we have a sort of black gray background and we have two different numbers and different colours on them. Take a look at that plate there. What number would you be able to see?

Katie - To me it looks like a red 2. And then a pink 6. So 26 on a grey background.

Sonam - Absolutely. And for someone with a specific type of colour vision deficiency, whether it's red that they struggle with, whether it's green that they struggle with, they may only see one of those two digits on there rather than both digits.

Sonam - For us, we can see them equally. They're both just as easy to see. For someone with a deficiency, they may be able to only just see the 6 and not really see the 2 very well at all. So there'd be a distinctive struggle with being able to see it.

Katie - So what's going on there? I imagine there's quite a few different types of colour vision deficiency, but in this example, what would your diagnosis be? What is the problem?

Sonam - So this patient would have definitely a congenital colour vision deficiency, whether that's red or green. The idea is that they go through all four plates of this background that we have. And using that scaling, we would then be able to determine whether it's likely to be a red deficiency or likely to be a green deficiency.

Katie - Whilst informative, Sonam told me that the Ishihara test isn't really the gold standard. So if an optometrist suspects you might have less than perfect colour vision, they might send you for further tests. And speaking of tests...

Sonam - You have very normal colour vision!

Katie - Okay, that's a relief! Having said that, would I necessarily know if I had a problem with my colour vision?

Sonam - It may not be necessarily that you're aware of a deficiency unless you come across a particular scenario where you find yourself struggling. Um, a lot of times people can get through life and not be aware until they hit that point in life where suddenly they've realised, actually I'm really struggling with this task. And it can be simple things like being able to cook meat or looking at fresh fruit from raw fruit, not being able to take those colours. So it can be general daily life activities which we take for granted.

Katie - Can you not get colour vision problems throughout life? Do you have to be born with say two cones and not three?

Sonam - The type of deficiency you're likely to get that's acquired or obtained through life is generally a blue-yellow type of deficiency. There are some conditions where commonly known as the red-green deficiency can be obtained through ocular disease. So if something goes wrong at the back of the eye, but even then the blue-yellow type is more likely to occur: that one's the one that occurs if things are going wrong at the back of the eyes.

Katie - Does it tend to be associated with age?

Sonam - A lot of the time, yes. So things like macular degeneration are more commonly occurring when someone gets older. Likewise with things like cataracts, also an age related process, there can be other systemic conditions as well. So things like diabetes. If there's diabetic retinopathy, so bleeding at the back of the eyes, then that's likely to cause shifts in colour vision as well.

Katie - So in that situation you've got a chronic condition which may have a consequence for your vision. Is it ever the case that changes in colour vision could actually be symptomatic of a bigger problem further up in the visual system?

Sonam - Yes. At times it can indicate that there is something else going on. So earlier we mentioned that red-green colour vision deficiencies are congenital, that people are born with them. However, there are some conditions which can have an effect on the red-green deficiency, which are acquired and that's incredibly rare but it can be life threatening at the point where it can indicate high pressure in the brain for example, and that sort of condition would be a sudden difficulty in being able to discriminate the colour red compared to having never had that problem before.

Sonam - When someone does have a congenital colour vision deficiency, we can't do very much about that condition itself to get rid of it. The most we can do in terms of recommendations is having more of an awareness of the condition. Particularly for children. If a parent is advised that their child has a deficiency, then that parent can take responsibility in how they guide their child's education towards specific career goals. There are some occupations where a child would not be able to take part in once they reached that age simply because they have abnormal colour vision. Pilots, train conductors, firefighters: that field of work does require very specific colour vision because it can have an impact on that person's life and other people's lives as well.

Katie - Is there any evidence to suggest that having colour vision difficulty has an impact on your education?

Sonam - Well, this is what we're looking into at the moment. Accounts previously have suggested that people with a colour vision deficiency have struggled with tasks and activities, such as titrations when doing GCSE chemistry or looking at litmus paper for example. So those sorts of tasks which rely on the use of colour have been suggested as being a difficulty.

Katie - I notice you haven't used the phrase colour blindness.

Sonam - Colour blindness is actually a complete inability to see colours at all. Someone with a colour vision deficiency will have a shift in the colours that they can see. There'll be a restricted number of colours that they will be able to detect. Colour blindness would imply complete grey scale vision.

Katie - From what you said, there's actually not a lot that can be done for somebody who does have difficulties. What would someone like yourself suggest they do? Is it a case of lifestyle adaptation? Can you do anything to help?

Sonam - It can be more simple things like labelling. When we go to a grocery store, if we're choosing apples, we look at red apples, we look at green apples. There can be some confusion for someone with a colour vision deficiency, so whether it's having more of a description on just what it is that the person would like to purchase or if someone is using crayons or colouring pencils. Having the name of that colour written down as well can make things a little easier. Raising awareness and trying to improve accessibility is is the way forward.

Katie - Do you have any general tips for looking after our colour vision?

Sonam - With any eye related reasons, it's to have regular eye tests. A lot of the times some of the acquired deficiencies can occur because of medication that you have been advised to take. So it's always worth reading all, all the health and safety at the back of that instructions box or in the little leaflet inside. And likewise when you go in for your eye tests as well, let your optometrist know what medication you are taking. There are some medications that we almost have red flags for where we can double check colour vision a lot more and keep a closer eye on things. So whether that means more regular eye tests compared to just a routine two year checkup. That way if there is something that is cropping up, we can keep an eye on it. Or if we need to refer back to the general practitioner in regards to potentially discussing the medication. 


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