A Flash of Light: The Science of Light and Colour
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A Flash of Light: The Science of Light and Colour
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Product Details
| ISBN-13: | 9781782628590 |
|---|---|
| Publisher: | Royal Society of Chemistry |
| Publication date: | 07/01/2016 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 128 |
| File size: | 1 MB |
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A Flash of Light
The Science of Light and Colour
By Mark Lorch, Andy Miah
The Royal Society of Chemistry
Copyright © 2016 The Royal Society of ChemistryAll rights reserved.
ISBN: 978-1-78262-859-0
CHAPTER 1
Where Is Colour?
Giuliana Mazzonia
University of Hull, UK
At the moment, the therapy has only been fully tested on animals, but the results of initial clinical trials in humans suggest that it might be extended to pathological conditions in human colour vision in the relatively near future. Let's imagine what it would be like for a person suffering from colour blindness who undergoes this gene therapy and recovers colour vision.
1.1 A SUCCESSFUL STORY FROM THE FUTURE
"As I was walking to the train station this morning, I noticed the colours of the leaves on the deciduous trees around the house — gold, bright yellow, pale green, deep red. Beautiful. But, 'where is colour?' I was asking myself. The question comes from my own experience as someone who used to be colour blind. That's right, colour blindness can be corrected. In the beginning, my eyes did not work properly, but after a new rather revolutionary surgical intervention, I could see colours as they appear in the external world to other members of my species. What an experience!
My form of colour blindness is called achromatopsia and it is rather rare. You see, it turns out that most colour blind people do actually see some colour. What's more, there are various forms of colour blindness; some can see a couple of colours, although somewhat dull, others can see much less colour than most. Fancy names are associated with these various forms of pathology. For example, dichromats (mostly men) can see only two ranges of colour and, among those, deuteranopes present problems discriminating between red and green while others with protoanopia cannot see red and similar hues, those with tritanopia fail to discriminate blue hues. Other people can only see one colour, monochromats. Finally, there are people like me, who have complete color blindness, otherwise known as achromatopsia. People of my (original) disposition are completely colour blind, like the inhabitants of the remote island (the Micronesian atolls of Pingelap and Pohnpei) described by Oliver Sacks. Apparently, they also see the world the way I saw it, in shades of grey. I was the one in 40 000 born that year with achrmatopsia: 39 999 with good vision, and me. But all that has changed now, I can finally see colour.
Yet, a question occurred to me in my current state: Now that I see the colour of the leaves, does it mean that leaves really have colour? Which was the version of the world closest to the truth: is the world coloured? Or is colour just in the eye and the brain of the beholder? Before surgery, my world was mostly monochromatic. It is a rather strange experience to recover colour vision, especially at the beginning, when colour patches do not match the shape of the objects to which they are supposed to belong. I could see the shape of my car, but the red was floating somewhere near to it, and at first it did not 'stay' within the car shape. It was when I was recovering, and seeing those coloured patches outside of the objects they were supposed to belong to, that I wondered if colours do indeed exist in the external world, or whether they are only 'in the mind of the beholder'.
In some cases achromatopsia is determined by cerebral damage to areas in the occipital lobes, mostly an area called V4 (for visual) and specifically the lingual and fusiform gyri. Others, like mine are a special condition, in which little cells in the retina — called cones — were not working, while the brain was still intact. While most people think about the retina as simply a part of the eye, it is actually a part of the brain that was placed at the bottom of the eye. When all is going well, cones convert the electromagnetic waves of light sensory stimulus into electrical neural impulses.
Going back to my pathology, my cones were not working, because they were missing crucial proteins — opsins. These proteins react to specific light wave lengths and make colour visible. Without these opsins within the cones, there is no colour vision.
During surgery, genes that coded for the opsin proteins were artificially inserted into my cones giving my vision the range of colour that most people enjoy, more or less. The surgery was rather scary, but it had been successfully tested on our genetic cousins — other primates — before me, and had undergone some initial clinical trials on humans, so I was hopeful. It is a form of gene therapy and I am certain many more people in a similar condition as mine will volunteer to have it done. I will talk about the surgery later, but the core of my question remains, where is colour? Is it in the objects that we see, or is it in our eyes, or in the brain?
Living with colour blindness is not easy. A person who can see in colour cannot understand enough what colour brings. For example, there are emotional reactions innately connected to colour. Males seem to respond better to blue, females to red. Now, just to be clear, this doesn't explain why blue is sometimes associated with boys and why girls are associated with pink! That's a whole different ball game in sociological research. Nevertheless, even some forms of therapy are based on the realisation that different colours elicit different emotions in different people, even if some research suggests that specific emotions are elicited by specific colours in everybody (e.g. orange elicits friendliness, red excitement, green peace, etc). Also, people seem to respond to colour when making a purchase (does it mean advertisement and marketing strategies had no effect on me?) and colour responses can often play a big part in how our commercial world is seen. Curiously, the reason why Facebook's design is mostly blue is not because it was made by boys, but because its founder Mark Zuckerberg is red-green colourblind and can see blue best. Facebook apart, colour affects people's purchasing decisions, and marketing companies base brand colours on existing research in order to endear people to their products. Research made by companies has shown that specific colours are associated with specific attributions of product characteristics. For example, black is found to be associated with the idea of stability, credibility, strength, power, professionalism, accuracy; green with natural, organic, education, adventurous, calming; blue with cleanliness, medical, professional, judicial, business-like. Hence, to substantially simplify matters, black is good for solid corporations, green for ecological business and tourism, blue for medicine and science, etc. I looked at the website, https://blog.kissmetrics.com/color-psychology and indeed label colours convey — even to me — different impressions and emotions.
Typically, we also respond differently to pills of different colour. For example, even if they are totally inert placebos, i.e. basically just sugar pills, blue pills have a relaxing, calming effect, as do anxiolitics.
Red pills, on the contrary, have a stimulant effect, which is similar to caffeine. Taking a coloured pill has a greater effect than taking the same pill but colourless, meanwhile popping a coloured pill twice has an even stronger effect than taking it once. So, with all the perks that come with colour vision, being able to see only dark and light and shades of grey makes life rather difficult. Furthermore, although I have not been tested then, I might not have shown the same purchasing behaviors or the same placebo effect of red vs blue pills as most people do.
In some cases, colour is also essential for identifying objects. Basic object identification is due to the ability to detect the contour, the outline, of the shape of the object. In real life, the contour is not a black line, it is most of the times a difference in colour, difference linked to luminance, colour intensity, colour contrast. So, a person who is colour blind can experience major difficulties in identifying objects. While there are many different cues one can use that are not based on colour to distinguish objects, perception can remain partly impaired. Fortunately for me, I could see depth and so I never fell down any precipices, but driving was not really possible.
So, when I was colour blind, I could still see shapes and objects, distinguish objects from the context and the background, but lack of colours made object recognition difficult. The fact that colours are important is also evidenced by the history of medical doctors and scientists (chemists, for example) who reported their specific impairment and the negative effect of colour blindness on their professional activity, and the need to take remediational steps to overcome such limitations. Even if they are not painters, their professional life can be impaired.
Now they have tested me using a relatively easy method that they call nonmetric multidimensional scaling. It consists of judging (overtly) the similarity of colour hues. I am not performing yet as people who always had colour vision. All three types of cones in my retina are working; short-wave (S), medium-wave (M) and long-wave (L) cones. I can now see magenta, cyan and green, although the mapping of S, M and L cones on the three colours is far from perfect, though this is true for everybody.
When I was still recovering I was confused by colours for a while seeing, among other things, reddish frogs and bluish leaves! In normal people, green (medium) light waves activate the other two colours, as it is not possible to stimulate only M cones (so-called "green" cones). The other two are also stimulated to a certain degree, but the system has learned to discriminate among them. I needed to learn that too and the reddish frogs and bluish leaves became slowly greener over time. The opponent process of light vs. dark I always had been able to see. I am also starting to have the experience of blue vs. yellow and red vs. green.
I have talked a lot about colour, but again, still have not discovered its location.
When I said that I could not see colour, it was exactly like that, no colour coming from the outside world at all. However, there are people who, in spite of being unable to see colour at all with their eyes, still can see colour in their mind's eye. A great example comes from people who have synesthesia. These are somewhat special people in whom the five senses (and especially hearing and vision, but also touch and smell) are connected in an unusual way. For example, they can see musical notes, and music becomes a stream of visual elements. Often the visual association comes as colour.
For example I recently heard the case of a blind opera singer who sees the music she sings as a continuous stream of colours. Her children also evoke visual colours for her. Her daughter is very yellow, and her son is acid green. She cannot see any colour through her eyes, but she can see colour in her mind. It is true that she was able to see colours when she was young, before her vision completely deteriorated, but now her colour vision seems to be completely mediated by her brain. It seems that several non-blind musicians also see music in colour: Liszt, Rimsky-Korsakov, Sibelius, and the less known Joachim Raff who saw a different colour for each musical instrument.
So, once again, where is colour? Is it in the objects, as wavelengths, or in the brain as the experience of synesthesia suggests? The role of the brain in making sense of colour becomes even clearer in some visually impaired synesthetes. Such people can see colours they have never experienced in their life. One patient described by Vilayanur Ramachandran and Edward Hubbardcannot see at all certain hues, because of a deficit in color receptors. However, when looking at numbers, his synesthesia enables him to experience colors in his mind that he has never seen in the real world. He calls these "Martian colors". Well, I wonder what colour are these Martian colours, and I wonder if one can discover what they look like by making someone with this capacity choose among the more than 800 Munsell cards that contain an incredibly large variation of hues.
The fact that, in other conditions, people can see colours that do not exist tells us that colour is not in the objects. Some people, for example, can 'decide' to see colour in patterns that are just shades of grey. But how does it happen? Research carried out in 2014 in the Department of Psychology at the University of Hull examined a special skill present in about 10–15% of the population — that of hallucinating colours at will. People with this ability can see colour where no colour is presented. Such people are not at all gullible; they possess the enviable skill of being able to modify their perception as they like. They can stop experiencing pain, they can hallucinate sounds and even figures at will. So these extraordinary people were presented with Mondrian-style coloured patterns, or with the same Mondrian pattern, but this time in shades of grey. To a certain extent, the grey pattern resembled my kind of colour blindness.
When grey Mondrian patterns were shown, participants were invited to use their ability to alter their own colour perception and see a coloured pattern where there was none. They were then asked to identify on Munsell cards the exact colour hues they were seeing. In an additional condition, visual aftereffects of these intentional colour hallucinations were studied. For example, if you see red for a long time, for the rules of opponent process, you will see green if you then move your eyes to a white board. A substantial percentage of these particularly skilled individuals saw the grey Mondrian pattern in colour, with colours varying from red to orange to yellow to green. They never saw blue or purple or violet. Many of them also had visual aftereffects, which confirmed that they were not confabulating, nor being complacent with the requests of the experimenter. Rather, they were having a visual effect that involved colour when no colour was actually there.
Where do such 'hallucinated' colours come from? fMRI results on these individuals show that the same posterior brain areas that are involved in seeing colour were involved when they hallucinated these colours. Colour hallucinations are thus the result of the activation of one of the posterior areas of the brain, the lingual gyrus, which are part of the brain network responsible for seeing colour in the real world.
So, going back to my question, where is colour? In some instances, specific light waves trigger retinal cells, that much is clear. However, colour vision can be achieved completely independently of the physical external stimulus and so this is not a sufficient explanation. Moreover, the brain produce colours, even if no light triggers any reaction inside the retina's cones.
What can I then conclude? Are leaves actually green? One must conclude that it is actually the activation of the visual areas responsible for colour vision that are ultimately responsible for colour vision. If microelectrodes are inserted in those colour areas, then the person sees colour, even with closed eyes. The reason why the brain can produce colour is that, strangely, the brain areas have functional specialization. As there are neuronal clusters that react specifically to simple features as horizontal lines, or vertical lines, and there are neural clusters that are specialized to see faces, there are also brain areas that, if activated, produce the experience of colour. In short, we are born to see colour. More broadly, the act of seeing is, more often than we think, actually an illusion. This does not imply that all we see is always a hallucination and that the physical stimuli never play a role. Quite to the contrary. Although there are many instances in which seeing is possible in the absence of external stimulation (e.g., visual hallucinations), the visual system is also constantly activated in response to external light. However, even when responding to light, one should not underestimate the immense difference between the nature of the external stimulus and the final nature of the percept, which is exclusively the result of neural and brain processes. The green of the leaves is inside me, it is in my brain.
1.2 BACK TO THE PRESENT
While the previous fictional story illustrated the experience of a future person with complete achromatopsia who undergoes genetic surgery, here is briefly reported the case of an existing young man, Ethan, who presents a more common form of colour blindness. His vision is not in shades of grey, he can see some colours, but they are more dull than the way they normally look when the eye is intact. He can see some pink and green but, at times, the pink looks silver or blue, and green looks brown or yellow. This is due to how his retinal cones react to light waves of different length, which is different from the way cones normally work. According to his own account, his S cones, those that react to short wave length (blue range), seem to be relatively intact, which implies that he should be able to separate short waves from the others and see blue. He sees yellow because yellow is the opposite of blue. When activated, S cones cause us to see blue and, when inhibited, lead to seeing yellow. However, the medium (green) and long (red) cones do not discriminate well between these two different ranges of wave length, and the perceived colours then get muddled. So, Ethan sees green as brown. Recently, a friend gave him a very special pair of glasses, which separate medium from long light waves. To his utter astonishment, these glasses made it possible for him to see this difference and, for the first time, to see colours as they appear to an intact eye. Or, at least this is what he reports.
While these glasses are still an assistive device and not a cure, there is hope that, in the future, some types of colour blindness can be cured also in humans. Gene therapy has proved rather successful in a range of animals, including primates. Gene therapy is a very delicate procedure that involves the addition of the photo-sensitive pigments that are not working (the opsins that are missing in colour blind people) via a viral vector that is inserted in the appropriate cones. Red–green colour blindness, which is the most common form of partial colour blindness, derives from a deficit in either L or M cones, as it happens in Ethan's case. More specifically, the deficit is in the L and/or M opsins, the proteins that function as photopigments responsible for responding and elaborating long and/or middle light wavelengths. This is typically a genetic disorder. These people have dichromatic (two-colour) rather than the normal trichromatic (three-colour) vision. Adding the missing photopigment restores trichromatic vision. It was previously believed that no improvement in colour vision could be obtained unless the intervention was done on the very young (earlier sensory deprivation studies had shown that neural connections established during development would not appropriately process an input that was not present from birth). However, a 2009 study has demonstrated that gene therapy can be successful also in adult monkeys, which gives hope for future similar interventions in adult humans. Trials on humans are already under way.
Yet there are some problems in the delivery of the viral vector to the retina, as the virus has to be injected directly inside the retina using a needle. Besides being unpleasant, such a procedure carries the risk of infection. Furthermore, it is not yet known how many iterations of the injection one needs to go through in order to obtain a stable effect, and repeated injections can produce an immune reaction to the virus. So, it may well be a while before this technique is available to large numbers of people. But still, there is hope for a 'coloured future'.
(Continues...)
Excerpted from A Flash of Light by Mark Lorch, Andy Miah. Copyright © 2016 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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