I have often wondered what it feels like to be color blind, and what kind of life a person with color blindness leads. We often take for granted the fact that we can see color. What exactly does color do for us? Looking at everyday life, we need color as much as we need anything else to live. Traffic signals are color coded, what we wear, what we look like, what we eat, everything has a color to it. Now imagine a world that was just black and white. It would be the most boring and painfully simple world to live in. There would be nothing to distinguish us from another person... a red dress from a black one, and in this day and age, it could prove to be potentially dangerous. looking at it from a biological stand point, even our bodies are naturally color coded, from the inside and out. animals use camaflouge to protect themselves from danger, why would they need that if everything was black and white. for me color is very important, and it explains a lot about behavior. Without the use of color, behavior would have to be looked at from a different stand point, a much simpler one. Color adds complexity to ourlives and in a sense almost gives it a way to organize our lives...internally and externally.
See Oliver Sachs Anthropologist on Mars for a wonderful essay on a painter who lost color vision. Yes, an important part of our "reality", no less so for being "made up". PG
Our percept of color was probably once the most important function in the human mind. We needed to be able to distinguish color in order to separate out foods that were good for us and those that were poisonous. Color was thus a means of survival. But the body was developed through a random sequence of events and thus we were adapted to the environment that we live in which is why we can neither see actual photons nor wavelengths of color. The fact that the autonomous brain takes over the interpretation of the different ratios of long, medium and short wavelenghts is probably characteristic of the greater part of the brain being given over to concious "higher" thinking. It is an interesting question to ask whether artists have a more intimate closer relationship with color. Since perception is so individualitistic are there individuals in which the C areas are better developed and so they see more vivid colors?
It is interesting to note that color is an inherent property of the object> that we see by comparing objects to their surroundings. This is also a means of survival like our lateral inhibition network, we only distinguish by comparison and contrast. As with many things this was probably an adaptive measure, looking out over the horizon for a predator or prey. But, we have retained this adaptive measure, never seeing an object for what it is but what it is not. In this way behaviour and science are very close, they are comparing what they see and what they know, to what they do not.
As organisms we have had to develop in a less than perfectly organized manner, but the system works, thus since no better models have been developed we keep our general physiology. But since there are some faulty adaptations, the body has had to adjust in order to be able to accommodate and correct these faults. We are able to fill in the gap in the retina where the optic fiber leaves because the brain could not be left with a hole, and we are still able to see if in if the pigment is on the third layer. It is a sobering thought that we are never truly aware of everything around us, and because of the constraints of the system we will never truly see an objective reality.
It is an interesting, psychological question why colors have an ability to> affect our moods, the passionate red, the sombre blue, anxious yellow, are these the flags of mother nature to alert us to danger, red for blood being spilt or the paleness yellow of illness ? By our very natures we are able to impose certain feelings on our perceptions one of these being the association of particular moods to color.
Color affects our behaviour in many ways, it is a reflective measure of how much light is present, it affects our mood, but it is also a protective movement allowing us to compare and contrast better, than merely relying on the rods to detect movement.
Lots of interesting thoughts. Yes, clearly color has, for us, significance beyond being able to tell things apart (healthy food versus unhealthy food). I don't know enough about that to talk meaningfully about it, but others have written extensively on it. I do think there is an important GENERAL point there, which is that evolutionary adaptedness not only shapes things that work in an existing environment but also, in doing so, always creates the potential for new things (which may or may not prove useful/adaptive): that human color perception has significance beyond telling things apart is a good case in point. Yes, behavior and science quite similar: there is always the potential to find something new. Once can be sobered by the understanding that "we are never truly
Color vision between peole is very different. As we were discussing, some people are color blind, and some people have four wavelengths that they absorb light with. I also think that color and shape recognition can be a learned phenomena. After years of painting classes, I am much more attuned to color than most peole. I also pay a lot of attention to the particular shape of objets. I notice this enhanced perception in most aspects of my life. When my family goes backpacking, I always notice animals and flowers before any one else.I have noticed brown seals on brown rocks more than half a mile away, during dusk. What I noticed was that the pattern of light on the seals skin was more smooth and the pattern of light on the rocks. But besides this variation in pattern, there was no way to tell that it was a seal. The rest of my family could not see even when I pointed it out, and had to walk much closer to distinguish the seal from the rock. I am also very particular about assymentry in objects which should be symmetric. I shall never be satisfied by any pot that I make because I cannot make it perfectly symmetrical. This also translates into another phenomena. Becuase I concentrate so much on individual shapes, I cannot see those "hidden pictures" that are now popular. I cannot blur the overlaying confusion of colors to see the hidden picture underneath, even if I know exactly what the picture underneath should be. But I do pick out irregularites in the color spots on the top of the picture.
I think that some of this is a genetic phenomena, as I have always been good at finding animals and I have always had very good night vision. But I also think that this has a lot to do with my artistic training. In drawing, every angle of the obect must be scrutinized and compared to many other objects. The size of everything is compared to the size of everything else, and you become much more aware of shading. Also, I am very aware of all the variations of color in paint, so perhaps I am more attuned to diffences in color in life. It takes me hours to finish a painting, because I can tell variations in color between brushstrokes, and unless they are intentional, I have to fix them.I think that this training then carries over into a mechanism that becomes automatic, almost like learning to ride a bike. Perhaps the regions that compare color and shading become enhanced, or operate more quickly, so that you recive more information. While I cannot obviously see what everybody else sees, I think that there are great variations in what people really see, and that all of us have a very differnt perception of reality.
Wonderful set of issues from personal experience. Thank you. Yes, indeed, people see things differently. And yes, indeed, genetic and experiential influences both can contribute to those differences. Indeed, they can mutually influences each other. Your stories suggest the possibility that you saw things differently from others (at least in your family) before you became interested in art/painting, which in turn may contributed to making you interested in art/painting, which in turn further made you see things differently from others. Another interesting issue which your experiences raise is where in the nervous system the differences are. Seeing the seal on the rock a long ways away might have to do with focus or with aspects of acuity related to retinal structure or with something more central in the nervous system (or with all of them). The attention to differences others don't notice sounds more like an "I-function" phenomenon (though it might itself by triggered by something different in the pre "I-function" realm). Anyhow, its a wonderful set of thoughts, well worth persuing further. The relation between brain function and art has intrigued both scientists and artists for some time, there has been a fair amount written about it, and there remains at that interface a lot to explore. Let me know if you'd like to spend more time on it. PG
First of all I would like to say that i find the recent topics in class absolutely fascianting. I have never had an opportunity to investigate the anatomy of the eye and the question of seeing before, so the material behind the last classes is new and incredibly informative to me.
However there are a few associations/questions I have with these topics. One is with the way we percive reality. I remeber that in my high-school we were required to take geometry class. In those classes it was often necessary to know exactly what the picture of something looks like in order to solve the problem correctly. my teacher often was impressed with the ability of some students to do so. Apperantly enough, some people have really big problems trying to visualize pictures in several dimensions or even just parallel planes. Why is that? Is that something to do with the visual systems that we have discussed in class? I wonder about that, even though somehow it seems to me that the processes involved in seeing should not really be involved in whether you can picture something, or how you see it. In general the perception of reality is a quite puzzling thing. Why for example can some people see the pictures behind the 3-D images which are found in any bookstore these days? I definitely have problems doing that. Do you know what is involved in trying to see those pictures in terms of nervous system. It seems to me that you would only be able to see the picture if you try not to be involved in the process yourself and let the brain do all the work. IS that so?
Another problem had to do with colorblindess. I remember talking to a person who was colorblind. She said that she was only able to see in color when she was wearing esspecially desighned glasses, in which one half of the glass was colored red and the other one was clear. For some reason i can't find an explanation for this in terms of rods and cones. Can you help?
I was also thinking about other sensory systems that we are equipped with. Is sound similar to the visual system? I hope we get a chance to talk about that.
Oh, and I forgot to mention that it seems that we get better in seeing something with practice. Why is that?
Pleased/gratified by your interest in what we've been talking about in class, and challenged by your questions. Different people DO have different abilities to see and visualize things, as you suspect. I suspect not many of those are explainable in terms of the kinds of processing we were talking about in class, but at least some are. I share your difficulty, for example, in seeing the pictures in currently popular 3-d images (many people do), and we'll talk a bit in class about why that is so. No, I can't come up at the moment with a possible explanation for the two colored glasses (the red is likely to block color input from one eye pretty much, so there may be an eye dominance effect going on). Yeah, I wish we had time to talk about sound too. It shows some very similar phenomena (as do all sensory systems). Maybe another course. The getting better with time? Easy answer: something changes in the nervous system. The harder question: where/what/how? Probably lots of different answers (as will talk about a little later in course) PG
Color is an example of the variety and uniqueness of each person's behavior. Color does not have a uniform shade for all people. The color which I perceive for the green board in the classroom might be lighter, darker, or even a different color all together from the other students in the class. This difference is even more drastic with people who are color blind, since they have a different "color palette". This difference in perception of colors has different effects on behavior. For example, a child that is color blind but has not been diagnosed might have difficulties in school. During class he might have an exercise that requires him to distinguish between the two colors that are affected by his color blindness, say green and red. This would affect his behavior since he is most likely not able to see much difference between the colors. Thus the inability to distinguish between colors makes him exhibit an erroneous behavior which is not indicative of his lack of intelligence, simply the lack of perception of reality which is widely accepted by others.
This brings about another interesting point, the perception of reality. Our vision, including color, is heavily dependent and influenced by the brain. This makes everybody's experience of color unique ad not very true to reality. Our perception of reality is limited to our sensory processes which can, by no means perceive everything. Even those things that can and are sensed are not true representations of reality, especially color. The fact that it is our nervous system which creates the categories of color supports the ides that brain is behavior. Color is simply categories of the brain that are created by a simple connection of neurons. So behavior exhibited because of color is a result of the brain.
Yep. However, "our perception of reality" is INFLUENCED by, rather than "limited to our sensory processes which can by no means perceive everything". Remember that the brain can "make things up", and these are not necessarily limited by our sensory processes. So, we CAN in fact think about things in five spatial dimensions, even though our sensory processes are restricted to three. And we can use our categories to make new categories ... and those to make new instruments to detect radio waves, which we can't see, and so forth. PG
By distinguishing between wavelength and colour, and showing that the broad- band photopigment and its various forms responsible for the detection of different wavelengths do NOT detect colour, but rather incident photon energy (translated into wavelength for human convenience), colour can hence be thought of as an artificial construct of the brain imposed on reality. This has profound ramifications for our perception of reality.
If what we detect is not colour, then what does our world REALLY look like? And is there really any meaning to asking that question-- is there any absolute state of the world that different species, even different organisms within the same species, get only partial glimpses of through their specialised sensory apparatuses?
Much of our behaviour is based on being able to distinguish colour, being able to describe it and, in many cases, being able to reproduce it. Colour- blindness, then, presents an extremely interesting case because colour has such a different meaning for those who cannot detect what the majority of the population can. Sociologically, the dominant paradigm describes those people whose behaviour reflects the ability to differentiate between the red, green and blue primary colours. Thus, for example, traffic signals require differentiation in order to be able to function in accordance with laws set up by the general society.
Yep, profound ramifications for our perception of "reality". And for appreciating social conventions. Is worth keeping in mind that one can't, in general, presume all people are having the same experience. On the other hand, there is some substantial degree of ability of people to work with the same concepts at least. Which perhaps is the best we can do to try and get an idea of what the world REALLY looks like? Maybe better still if we understand better how it looks to different varieties of animals as well. Wisdom as the sum of lots of different "partial glimpses"? PG
Comprehending the true role of color in the nervous system and the form it actually takes in terms of a supposed input to the system indicates much about human behavior and carries implications for the general principles surrounding the nervous system. One of the first extrapolations one may make about the perception of color is that the system is incredibly complex and for a behavior that occurs without any knowledge by the I-function, it is much more complex than one may intially assume. The most significant complexity is the fact that there are actually two systems at work, one of which does not even percieve color. The scotopic system, used under conditions of low-light, does not perceive color but the photopic, under conditions of higher-light, does perceive color. It is essential, however, that both systems be in working order for the nervous system to output what humans associate as color. This therefore leads one to the conclusion that the nervous system is actually much more complex than the individual is aware and that certain aspects of the system that may intially appear superflous or unnecessary are essential for the functioning of the system.
Color may be received as a mix of wavelengths of light or a monochromatic light, but when it is received by the nervous system, everything is represented in the same manner. The actual colors that are perceived depend on the photoreceptors activated and they are also a product of the ratio between wavelengths received by the photopic and scotpoic systems. The fact that all color is represented the same way when received implies that the nervous system and the brain must be either manipulating the input and creating its own information that is then sent to other parts of the brain and received as input. One can infer that the nervous system actually constructs information in many instances and this may be one of the general principles of the activity of the nervous system. Furthermore, this implies that certain parts of the brain and the nervous system are, in a sense, "tricking" other parts of the brain, by almost disguising input. Not all areas of the brain are aware of what is occuring in its different parts, making the complexity of the system greater, but also making it more elegant. One may further conclude that behavior does not just arise from one bit of input, but it is actually a compilation of many different sources of input which are further manipulated and processed within the brain.
Good general points (though be a little careful, in general the scotopic system probably isn't necessary for high light color vision; its pretty inactive under high light conditions). Yes, indeed, all this sophistication goes on without the "I-function" knowing about it (until someone studies it and then teaches about it). And, more generally, what each part of the nervous system knows is only what other parts tell it, and a part of that is "made up" without any way to tell which part (at least, again, until someone studies it). And, yes, very importantly, behavior reflects LOTS of different inputs interacting (will see some more of that tomorrow). PG
The brain is able to let us see objects at a generally constant color eventhough the objects may be viewed at a variety of light conditions. For instance a vegetable like a cucumber on a sunny day allows us to know that its color is green. If the day were to be cloudy, since there is not as much light intensity we should 'see' a different color for the cucumber but we still 'think' it is green. Maybe this kind of constancy was for simplicity so that we would not become so confused with the endless variety of colors that can be portrayed with different light intensities. Maybe the identification of limited number of colors is a form of adaptation which has evolved through time.
The three major pigments in the cone cells of the retina allow us to categorize the colors of objects. But what is the significant purpose of color? Color does not seem to be such an essential factor for survival. Those who are color blind seem to function well in everyday life. Just seeing black and white does not affect the clarity of the objects I have personally seen.
Since there exists numerous wavelengths for the color spectrum, different organisms have access to different colors. What we see as a cucumber may look as a different color to certain organisms. Certain insects for example see different wavelengths of color around flowers in which we humans are unable to detect with our own eyes. Maybe we do not need to see such explicit colors in order for us to survive. The three pigments which interact to show us the colors we 'see' may be the the only colors we need to function in this world. It is also said that individuals may have different opinions about a certain color. Through my experience I have had instances where another person and I disagreed on what the color was for an object. Are there individual differences for seeing color?
Yes, there are indeed (for a variety of reasons) likely to be individual differences in characterizing the color of something. For all the reasons you give (and more), what "color" corresponds to is a pattern of activity in your brain, and the same input may cause different patterns in other peoples' brains (or even in yours, at different times; at night, for example, photons of a particular wavelength don't create a sense of color). The purpose of color? Presumably it helps us survive, as you say, but that doesn't take one very far. All organisms that currently exist have internal organizations that help them survive and, as you point, out these involve a variety of different "color senses", so it certainly isn't true that there is any "best" one. Clearly, though, color sense helps us to discriminate things we couldn't otherwise discriminate (red lights and green lights, for example). And, in this sense, people with color blindness have a "deficit". Correspondingly, all of us would in fact see "less clearly" if we worked only in light intensity (black and white) without being able to discriminate wavelengths. PG
"Just because you don't see it doesnt mean it isn't there"--i just sat down to type this essay, listening to music and that was one of the lines of a song---kind of interesting considering that was kind of what i was planning to type about. I am getting myself confused about the whole concept of color. That is what it is, right? a concept. and idea. i'm just going to ramble a little because i can't seem to organize my thoughts.
i mean, what exaclty is color?????? in class, we discussed any three arrangements of monochromatic light could arrange themselves to produce the same color as one other monochromatic light. but the brain creates the categories of color so who's to say that i am not seeing an entirely DIFFERENT green than the next person. maybe it is just that our brains have labelled that specific wavelength green. if we defined categories to be simple circuits of neurons then there is no way that anyone's category is going to be the same. no one has identical neurons and certainly not identical circuits. if we did, then where would autonomy fit in? it is the uniqueness of neural circuits that can account for many differences in behavior so obviously our circuitry differences are going to influence our perception of color. so what happens when i'm weaing a purple shirt (or so I think so) and someone says "nice blue shirt"?? is it that we are: 1) using different categories of "purple" and "blue" 2)there are differences in our photoreceptors 3)different photons have been activated by the same wavelength (is that possible? ie. one is more sensitive to 500nm) i understand how drastic differences in color can be explained, like red/green colorblindness, buthow do we account for the little differences?
Not too confused, I don't think. Yep, color is a "concept", an "idea", a "category" which results from the way the nervous system is organized, beginning with the photoreceptors themselves. A particular red (long before it gets a name) is a particular pattern of activity in the photoreceptors, which does not always result from the same photons. If someone else reports it differently, they might be using a different name for the same pattern of activity or might have a different pattern of activity because they have different photoreceptors or pigments or patterns of connections. That help with the little differences? Is sort of amazing there aren't more BIG differences than there are, huh? PG
From thinking about the ability to see color, it is apparent that the brain makes up much of what we interpret as characteristics of our environment. That is, we assume that objects have color, however this is false because it is actually the brain that asigns color to objects based on the wavelength of the light reflected. I then wonder if since everyone's brain is slightly different, could each person interpret the wavelengths differently so that the colors I see are different than those someone else sees. The only similarities are the names we assign to the specific wavelengths. Clearly, it can never be determined as a color cannot be described without relating it to another color.
Yes, it is certainly true that different people may have different internal experiences associated with "color" (as well as with other things). Which makes it all the more important that people share their experiences, with the objective of taking advantage of their differences to generate a larger "reality". PG
Exploring the input side of our box nervous system model through the eye introduces many paradoxical messages about how we think. Knowing the fact that we make up much of what we see, this brings doubts about individual perceptions, such that it seems like to get an idea of what an image really is, one has to ask a lot of people!! In addition, the fact that our range of senses is quite dull compared to many other organisms suggests that we are a bit simple. However, on the contrary, the fact that our brain can actually make up a great part of the image that is not detectable just by our sight is remarkable and makes us indeed, very bright and advanced. I think that it may be interesting to explore the evolutionary basis, if any, for this retinal processing, if perhaps there is some advantage to how we see, such that maybe we can better integrate images to thought with this kind of processing. It would also be very interesting to see what kind of visual processing man was capable of, throughout his development.
That's the bottom line, alright. If one REALLY wants to know what's out there, it helps to talk to LOTS of people. And hope they all see it a little differently. Yes, interesting to try and understand why our brains work the way they do ... and most important that they CAN entertain the idea that the particular way they see them is limited. PG
I have a couple of questions regarding color and the prevalence of disorders surrounding color eyesight.
I have been thinking about the issue of not seeing color at night. Is this because of the lack of photons stimulating the cones? Or is there possibly an inhibitor when the photoreceptors used for night vision are activated. It seems that there is a difference between not being activated and being inhibited.
Regarding seeing light at night. How are we so able to distinguish between red light and green light while driving in the evening if we need to adjust to the dark as we drive. It seems that at night, it takes no time at all to determine the color of a street light. Is the white light behind the colored screen instantly stimulating the cones in our eyes?
Disorders. I still am not clear on what color blindness is. The difference between red-green color blindness and other types of color blindness is very unclear (no pun intended). Is red-green color blindness the failure of our photoreceptors from absorbing shorter wave lengths or longer wave lengths of light. In class we talked about what wave lengths of light are absorbed, and the resulting color observed but I am still confused. Do our photoreceptors absorb the wavelengths we see, or the wavelengths that we don't see? I know this is a pretty fundamental point, but I want to be clear.
Clarity (pun intended) important. One doesn't see color in a dark forest at night because the intensity of light coming from all point sources is too low to activate cones. Yes, in principle it could be because cones (or something in the subsequent cone pathway) are inhibited, but in actuality the differing absolute light sensitivities of rods and cones provide an adequate explanation (at least to a first approximation) without invoking any inhibition. When driving in the dark along a city highway, the point sources of light which are street lights, signs, billboards, and so forth are of higher intensity, so they DO activate the cone system and one sees those parts of the night scene in color. That clearer? As for color blindness, the most common forms are two different versions of "red/green" color blindness. In one, the long wave length pigement is missing; in the other, it is the medium wave length pigment that is missing. Because the two pigments have largely overlapping absorption spectra, the consequences of missing either are pretty much the same: difficulty in discriminating wavelengths toward the long wave-length (red) end of the spectrum (wavelengths long enough so they are being absorbed by, pretty much, only one pigment, where normally they would be absorbed by two), hence confusing "reds and greens", both of which (as well as all intermediate hues) are seen as they same "color". Photoreceptors absorb the wavelengths we SEE; we infer the ones we don't see (ultraviolet, infrared, etc). See? PG
In realizing that color is a perception created by own our neurons, it may be in our best interest to look at other behaviors this way as well. From the start I have tried to understand behavior as a very complicated phenomena that depends on reactions and interactions. But sometimes, behaviors come about as reponses to stimuli that don't exist.
Many people with behavioral "problems" perceive things that other people do not and then react improperly. An example of this kind of behavior is hallucinations which are also visual concoctions. Yet these fictions must also be considered behavior because the neurons create for some purpose or in reaction to some internal or external stimulus-- although we may not know from exactly what.
It is important to consider even these "deviant" types of behavior (or perception) as valid and important because we learn a lot about the functioning of the mind by taking a good account of these things. Knowing that color is a perception created by a reaction of the cones and ganglion to different wavelengths of visible light may eventually help us to understand what other kinds of stimuli can cause such puzzling stimuli as hallucinations. In a way we might already have a link because phantom limbs can be seen as a "created" perception via the touch neurons. Now that we can understand phantom limbs as a phenomena caused internally and not externally it is easier to understand that color perception is not unlike feeling a non-existent limb. The only difference is that color perception most definitely is created as a reaction to the external world (wavelengths of visible light).
Interesting and appropriate extensions. Yes, recognizing that the brain "makes up" color does encourage one to appreciate that different brains may interpret different things differently. And the phantom limb discussion helps one to appreciate that "making up" can occur either in reaction to an input or in the absence of inputs altogether. All of which tends to blur the border between "normal" and "abnormal" behavior. Clearly, if we're going to take all this seriously (and I think we should), we're going to have to deal with that problem. I'm not sure we can do a finished job in this course (in fact, I'm sure we can't), but its a good one to get a start on, so everyone can keep working on it. PG
Our observance of color is an extremely sensitive observance of a small part of the electromagnetic spectrum. Strangely, all the other wavelengths in the spectrum are foreign to us and operate on what seems like a whole different system in practice, a system of dull and repetitive as opposed to vibrant, dynamic signals. But, it is our nervous systems which have transformed light into something more than predictable waves by tuning our receivers to pick up and elaborate on each exact visible light wave.
The course of our class lecture and discussion has pointed to the conjecture that to our nervous systems, color is as constructed a perception as solid space, with our sensitivity to color depending only on three special molecules that were randomly selected for to be held in special regions of our eyes. It saddens me somewhat to think that color, which we previously thought to be so inherent to each object and living thing, is as fragile as those tiny molecules in our eyes or does not even exist. Color is really more like an abstract idea than a physical property. We rely heavily on color in our lives (for example to tell us if a food is alright to eat), but in class we see how easily our eyes can trick us into believing that objects have properties of color and solidness that they do not. We find beauty in color, yet it was created somewhere between our eye and I-function, and not by light and an object. Color shows us yet another example of how our nervous system has specialized itself to filter and obscure inputs so that our mind senses and acts in a sort of a parallel world to that which is outside the nervous system.
I'm not sure the molecules are so randomly selected (remember natural selection is operating); after all, they do, as you say, help us to detect differences between things which are important to us. Yes, color is an abstract idea, but is that really a source of sadness? One might make an argument that "reality" (assuming its out there) is generally dull and repetitive, and that it is one of the excitements/glories of the nervous system that it gives it "color", no? PG
Why does a mixture of red and green paints produce brown, while a mixture of the particular wavelengths of light corresponding to red and to green produces yellow? In other words, what is the difference between these two processes which is responsible for their surprisingly different outcomes? The difference between additive and subtractive color mixing may be very easily explained in terms of what we have learned thus far about the visible part of the electromagnetic wavelength spectrum and about the anatomy and functioning of the eye. Mixing paint is an example of subtractive color mixing, in which certain wavelengths of light are blocked out from the wavelength mixture before ever reaching the eye. Taking as an example a green and a red pigment: a green pigment might reflect all wavelengths of light from about 550 to 650 nm, and absorb all wavelengths of light from about 400-550 nm and 650-700 nm. A red pigment might reflect all wavelengths from about 625 to 700 nm, and absorb all wavelengths below 625 nm. When these two pigments are mixed, their absorbtions work against one another so that only a restricted range of wavelengths are reflected:
400 450 500 550 600 650 700The wavelengths that are reflected correspond to neither of the two original colors in isolation, and are perceived as having a "new" color (in this case, brown). Mixing light is an example of additive color mixing, and is different from subtrative color mixing in that all mixing is being done in the eye itself. Continuing with the example of green and red: a "green" light might contain all wavelengths of light from about 550 to 650 nm, while a "red" light might contain all wavelengths from about 625 to 700 nm. When these two lights are shone onto one spot on a wall, all the wavelgths that compose both lights individually are refected into the eye simultaneously. That is,| | 400 450 500 550| | 650 700 GREEN 400 450 500 550| |625 650 700 RED
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551 - 624
The reason why yellow in particular is seen is rather complicated, having to do with the layout of the spectrum. However, the logic behind the difference between additive and subtractive color mixing in color vision is very clear and simple.550 600 650 GREEN
| | 625 650 700 RED
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550 ------------------- 700
VERY nice explanation of the difference between additive and subtractive color mixing, which I didn't have time to go into in class (and probably wouldn't, in any case, have done so clearly). Have thought about doing something which involves teaching as a career? Can be VERY satisfying to the right sort of brain (one like mine), and seems to me a very important thing to be doing in terms of current social/cultural needs. PG
The major issues that has become more clear to me is the way that the nervous system makes sense of the world is by receiving patterns of information from a variety of sources and then learning to interpret them (label them) as something. From color vision, we see that color is perceived based not only on the intensity of light (high light versus low light conditions), but also on the wavelength of light in high light conditions as well as the reaction in the receptor (cones). The light creates a reaction in the cones by a pattern of photopigments which will be different based on the wavelenght of light. Thus the nervous system receives a "code" of information from the type of receptor stimulated, the wavelength of the light and the photopigments used which it learns to interpret (and label) as a certain color. It seem our behavior, then, is based on our interpretation of patterns of input from many sources on the type of receptors stimulated, as well as from what is not stimulated (lateral inhibition). In high light conditions, a certain color creates a patterns of activity based on the cone photopic system which the brain learns to interpret as a specific color. Slight changes or variations in the color red will be detected because the pattern of activity will be slightly different. Thus our behavior is based on our ability to detect and transmit information, as well as our ability to code the pattern of activity and label it.
It seems that most sensory perception operates in a similar manner. Stimuli are detected, membranes are depolarized, a pattern of activity is transmitted (while other is inhibited) and the brain learns to interpret this in such a way that we begin to experience reality. The nervous system is set up to detect change or difference, and through detection and analysis of these differences it creates reality. Much like non color vision tells us mostly about the edges (or the change) color vision tells us about the difference of one wavelength versus another and about one photopigment in relationship to another (color mixing). In this way we perceive the world. Similarly, I would suspect our other sensory systems operate to detect change. The tactile system, for example uses information about the area of the skin stimulated (which receptors are stimulated) and which are inhibited (lateral inhibition) as well as information about how quickly the signal is being transmitted (intensity) and how sharp the stimulus is (based on comparison of areas stimulated and inhibited, to make a perception of what just happens. The nervous system learns to interpet this and thus uses this information to tell us about reality.
Yep, color vision principles certainly generalize to other systems. And detecting differences certainly important in all of them. So too the somewhat arbitrary character of the initial transduction. I think, though, you underestimate the nervous system a bit in saying that the brain "learns to interpret" this. Much of the "interpretation" and consequent creation of meaningful categories actually happens in the transduction and shortly thereafter. So, for example, it is the particular set of cone pigments which actually gives rise to the concept red, or at least to the kind of distinctive pattern of activity for which other parts of the nervous system need to develop a concept (in organisms that do such things). PG
The discussion of the way in which we see and an image is formed in our head reinforced my opinion that the nervous system controles our behavior almost exclusively. The NS filters information for us and adds new information without us, or the I-function, ever being aware of it. Even if we allow that the process of making a decision is not exclusively conducted through interaction of neural pathways and corrolary discharges, and that something that we could reffer to as the I-function participates in the process, we need to understand that the information the decisions is being based upon is not objective because the NS has already filtered it. This implies that the NS has the ultimate control over how we perceive ourselves and the world around us and consequently how we behave.
There certainly IS a lot that is going on without US being aware of it, which is to say without any information about how its done reaching the I-function. But don't be TOO pessimistic. The nervous system is a part of US, and WE (at least the I-function) a part of it. And WE can in fact come to understand (or at least improve our understanding) of what the other parts of the nervous system are doing before we find out about it. PG
When I was a kid I had the idea that a color blind individual saw something that was akin to the image projected by the old black-and-white television in my parents bedroom. Based upon what we learned in class it seems that this may not be the case. F or one thing what a color blind individual may see depends on which photopigment or pigments they are lacking. It has been made clear that a color blind person sees the world in a way that is different from anyone having all three color pigments. My que stion is this: Is there anyway (short of inducing permanent eye-damage) in which a person with color vision can experience was a color-blind person sees?
Depends on what form of color blindness one is talking about (there are lots of kinds). The best understood involve absence of one or more of the cone pigments. Complete absence of the cone pigments presumably gives sensations comparable to what you get at night when you are using only rods. One can also to some degree selectively bleach a cone pigment, which gives some idea of what missing one would be like. Color blindness can also result from more centrally located brain lesions. Oliver Sachs in An Anthropologist From Mars describes his experiences with a person having such a lesion. Its well worth reading. No, its apparently not like black and white television. PG
Color seems so obscure right now. We see it all of the time, yet there is so much processing that goes on nearly instantaneously. It is surprising that most people have the same ideas of colors in their brain. There is so much talk about how people are different and how raising a child in a particular way can affect how that child behaves later in life. Knowing that color is (or may be) phony, i question how it is relatively constant. Like every other output we have studied, our interpretation of color is a pattern of activity across neurons in the brain. The input we are working with here is also a pattern like with output.
Behavior is too complex. We pick at little parts and see how much goes into just a little bit of output. I like learning about color vision and I understand how it works. I do not quite see your justification for why it is phony though. Depending on whether photons hit rods or cones determines color or not. What is wrong with that? It just means that we need a more intense light to be able to see color. And there also seems to be little problem with the idea that three separate wavelengths can produce the same color in the brain as one monochromatic light. We know that from playing with art when we were younger - how colors could mix and create other colors. Although light follows slightly different rules, it does not surprise me of the results or lead me to think that color is not for real. Am I questioning?
Yep. Are skeptical. Which is fine. Hope, by the end of the course (maybe that's too soon? we can keep working on it after), the deeper issues making you skeptical will become clear. Regardless, I agree that what we know raises interesting questions about how come different brains exhibit such agreement (presumably because, despite their differences there are also substantial similarities, AND because, despite the inability to KNOW there is a real world out there, our collective experiences strongly suggest there is something stable influencing all our experiences). All of which bears on the "phoniness of color". No, there is nothing particularly surprising in the observations which lead to that conclusion: things don't looked colored unless they are bright enough, and colors when mixed together give other colors. What is surprising to many people, and is I think important in any case, is that "color", as we use the term in everyday discussion, is a concept and category created by the brain, one which makes sense only in those terms, rather than an attribute of the (hypothetical) external reality in which we live. What is "real" (as far as we know) in the external reality is wavelength. Photons have wavelengths; what they don't have is "color". Three lines of evidence. First, the same photons produce "color" is absorbed by cones, do not produce "color" if absorbed by rods. Second, a particular color is perceived if particular photons are absorbed by cones, but can equally well be perceived in the absence of any of those photons when appropriate mixes of other photons are absorbed by cones. Third, a particular photon, or mix of photons arising from a given point source, will give rise to different colors, depending on the photons being absorbed from other point sources in the visual scene. In short, color corresponds to a particular pattern of activity in the brain, which bears no one to one relationship to the wavelength of the photons being absorbed. Color is very "real", to US. It just doesn't happen to be, as we usually think, an attribute of external reality. That help? PG
From thinking about the ability to see color, it is apparent that the brain makes up much of what we interpret as characteristics of our environment. That is, we assume that objects have color, however this is false because it is actually the brain that asigns color to objects based on the wavelength of the light reflected. I then wonder if since everyone's brain is slightly different, could each person interpret the wavelengths differently so that the colors I see are different than those someone else sees. The only similarities are the names we assign to the specific wavelengths. Clearly, it can never be determined as a color cannot be described without relating it to another color.
Yes, it is certainly true that different people may have different internal experiences associated with "color" (as well as with other things). Which makes it all the more important that people share their experiences, with the objective of taking advantage of their differences to generate a larger "reality". PG