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Neurobiology and Behavior, Week 12

Paul Grobstein's picture

Welcome to the on-line forum associated with the Biology 202 at Bryn Mawr College. Its a way to keep conversations going between course meetings, and to do so in a way that makes our conversations available to other who may in turn have interesting thoughts to contribute to them. Leave whatever thoughts in progress you think might be useful to others, see what other people are thinking, and add thoughts that that in turn generates in you.

You're free to write about whatever came into your mind this week, but if you need something to get you started ... Our explorations of the sensory side of the nervous system have turned up evidence of that what we perceive is a construction of the brain, an informed guess based on presumptions of which we're not aware and that might be otherwise.  How strong do you feel the evidence is on this point?  In what ways does it help to better understand behavior?  What new questions follow from it?    


JJLopez's picture

Something wrong with my vision?

It makes sense now that our eyes have special cones and rods that transition the eyes from light to dark.  Thinking about my eyesight, I think I have some type of defect with transitioning between light to dark.  With most people, their eyes adapt within a few minutes from light to dark.  However, I think my eyes never really adapt.  When I am at the movies, I can't see at all and struggle getting myself a seat because I can't see where the empty seats are and when I do find a seat I can't see the difference between people sitting in the spot or where peoples feet are because I just see pitched black.  When I have to get up I have to look for the orange/red lights to the side of the isles because I can't see anything in front of me.  Also, when I am in a car at night I can't see anything that is going on outside of the car, my eyes just see pitched black.  I get scared when I am on the train at night and the conductor doesn't announce the next stop because I can't see what we are driving by. Also, I can't drive at night because the lights from the other cars blind me and because I already can't see what is happening outside of the car, the lights coming towards me make it worse.  Is this something common for most people or not? 

yml's picture

Color, brain, perception...

Now I think about it, I always knew that what we perceive is a construction of the brain and there is no absolute truth in the things we see (or there is, but we wouldn’t know). I knew about color blindness, illusions we experience, and that colors on objects are really the different rays of color bouncing off the surface and how we perceive. Yet, it surprises me every time I experience some illusion tests, like the blind spot test and checkerboard example, and can’t believe how unreliable my brain is. I think I expect something more than “informed guess based on presumptions” for our brains.

Since we talked about how our brains perceive color this week, I was wondering, can we tell how differently we each perceive color? One can say something is red and another can say it’s orangish-red. But maybe, their brains are perceiving the color exactly same, but their explanation of the color is different. If we ask them to choose a color on the paper that best matches the color they see, they might choose exactly same color. How can we then tell they are perceiving it differently or are they perceiving it differently at all? Unlike illusions, for example like checkerboard example, where there is absolute truth and there is way for everyone to see the “answer”, color is much complicated concept, because subtle difference in the hue or shades of the color is difficult to verbally explain.  


natmackow's picture

Wavelengths, color and the brain

In class we discussed the notion that color is not a property of the world or of light. Rather it is a construction of the brain (and it is most likely constructed differently in different brains). It was also mentioned that color is fully dissociable from wavelength. I wonder if it is possible for humans/animals to naturally see only in wavelengths? If this were true, however, would they just create mental constructs for what each of those wavelengths means to them? Would it be more adaptive for certain animals to see less “color” (for example, dogs are known to be red-green color blind)?

This whole discussion was interesting to me because of the book I recently read, An Anthropologist on Mars by Oliver Sacks. In his book, a patient, Jonathan I. (a 65-year-old artist), was in a car accident. Afterwards, Jonathan had transient amnesia, transient alexia (inability to read), and the inability to see color. This was devastating to the artist who had been known for his vibrant paintings. What was going on in his brain to cause this inability to perceive color? The phenomena occurred too quickly for it to be due to damage in the eyes, and in fact the patient reported that his “vision had become much sharper, that of an eagle.” Damage was not visible on CAT or MRI scans, but clearly something was altered in the portion of the brain that integrates the input from the eyes and constructs color. This was not limited to him seeing the world around him. Jonathan I. was also unable to construct color in his mind, his memories, and his dreams. He was unable to remember what color ever looked like. The patient was tested and it became clear that he could discriminate wavelengths! Could it be that all humans are capable of discriminating wavelengths in this manner? Do we just not realize this ability because our NS’s automatically construct colors from these wavelengths? This would make sense, because the damage to Jonathan’s brain seemed to have affected his ability to “translate the discriminated wavelengths into color”.

Schmeltz's picture

Dickinson Revisited

As we have been discussing visual perception, I am becoming more and more convinced that our interpretation of Emily Dickinson's poem is correct. However, the presumption that my experience of things is not the actual experience of things, but rather a brain construction, is still a challenging concept for me to accept.  I do not find the explanation to be wrong or insufficient in anyway, it just has raised a lot of questions for me about what actual capabilities and experiences I have, "I" meaning my I-function. I guess I can make it simple for myself and just say the I am my nervous system and nothing more. I guess I could say there is no actual mind, soul, spirit, I-function except that which my brain creates. I guess I could also be less pessimistic and say that while I am my nervous system, I at least have a nervous system that is able to construct an idea of an of me, I, and Tessa. I can look at it as if I have a highly imaginative nervous system, a nervous system "wider than the sky", that is continuously producing complex compositions of the world. However, because I also have this idea of "I" and this idea of mind and soul lurking about in my brain, I become maybe a little bit disappointed that I am all brain. Yes, I am still underwhelmed by the notion that it is all brain even though this notion in a way expands my possibilities and capabilities.  I can do so many things without even thinking about it - without even having an I-function. Without my nervous system taking precedent, there would be no color, no 3D, no visual experience. My compositions, even though they in fact are not reality, are still amazing given the fact that it takes very little effort to create them. I look outside right now. I see blue sky. I can sense that there is wind outside by the way the trees are moving. Pink cherry blossoms. Green grass. People walking around and about. In seconds, I have created a picture outside without stressing or thinking. Just observing. No felt energy expended. Knowing that I am not really seeing what is out there is quite a trip, but I guess it does not make it any less brilliant.

Another question that keeps coming to mind is why do I even need this I-function? It is kind of getting in my way...

Also, in terms of the color, we said that yellow is NOT 550nm of light but rather the activation of 2 cones. It is the result of color mixing and the relative activation of one cone to the other. We said that the color we are experiencing is NOT the result of the wavelength of light, but rather the arbitrary distribution of photo-pigments. But is it not possible that the "color mixing" or distribution occurs in a way that produces a particular wavelength, say 550nm that is perceived as yellow? If 550nm is not yellow, and if wavelengths do not actually correspond to certain colors, why are we taught this idea?  

cschoonover's picture

Perception and Color

 I think that right now the evidence for the process of “filling in the gaps” is strong, I just need more to help me understand. In terms of behavior, it makes a lot of sense that what we perceive is not necessarily what is out there. To “see” what is actually there and not what our brain is guessing at would require a lot of high level processing at extremely fast rates, because we would have to be able to discriminate so quickly (and be cognizant of it). Previously I’ve tried to determine how instincts can be evaluated in the parameters of our class discussions, and I’m now wondering if they can be interwoven and/or here. It seems to me that instincts are factual evaluations of one’s current situation, evaluations that occur on the unconscious level. But if what we perceive is really just a construction of the brain, then how accurate are our instincts? How can we be sure that when our “fight or flight” response kicks in that it is actually the correct response to the situation? And what about those instances when we just know something bad is about to happen? What is the mechanism then? Clearly the factors that contribute to our perception of the situation are things we are not aware of, but how are they translated into instincts if we can’t be sure of what we are seeing/hearing/experiencing?

I thought it was interesting that when we describe colors we aren’t necessarily referring to the same thing. In society, we pretty much have a defined color for most everything and the majority of the population adheres to this assignment (as evidenced by the number of little kids who prescribe to the hundreds of colors in the Crayola crayon box). So how is it that, despite our inability to see every color in the exact same way as another person, we as a whole have come to recognize “blue” as blue and “red” as red, etc.? 

Saba Ashraf's picture

Perception of Color

            Learning the differences between the rod system and cones was very useful in understanding color. When we discussed the rod system in class, it made a lot of sense that we couldn’t see color, but only light. The same permeability changes and signals were occurring for different wavelengths of light, so the brain had no way of distinguishing these signals. I found the point about color being a construction of the brain also very interesting in class, but in particular that colors can be constructed differently in different brains. I have always assumed that my version for example green is the same for every other person, but since color is a construction of the brain, this can’t always be true. The idea that colors are a construction of the brain does make sense to me in certain situations when different people can’t agree on one color being for example purple. In this case, two different people perceive the color as two completely different colors.

It is also amusing to think about the fact that to this day there really is no exact way to describe colors specifically even though they are a part of our daily life. However, I don’t think there are concrete ways of describing a specific color anyways since we all perceive them differently.    I also found the point that colors are fully dissociable from wavelengths to be very interesting because I was always taught that a specific wavelength needed to be prevalent to see a particular color such as red. I would be interested in learning more about being able to perceive colors without having that wavelength of light available.  

skim's picture

you see what you want to see

In reply to Colette's post, I also wonder how much of what we physically perceive is selected by the brain.  I came across this article on about a study conducted by two University of Delaware psychology professors (published in April 2010 issue of Emotion) about how jealousy can literally make someone blind.
I went on Tripod and tracked down the abstract:

Does the influence of close relationships pervade so deeply as to impact visual awareness? Results from two experiments involving heterosexual romantic couples suggest that they do. Female partners from each couple performed a rapid detection task where negative emotional distractors typically disrupt visual awareness of subsequent targets; at the same time, their male partners rated attractiveness first of landscapes, then of photos of other women. At the end of both experiments, the degree to which female partners indicated uneasiness about their male partner looking at and rating other women correlated significantly with the degree to which negative emotional distractors had disrupted their target perception during that time. This relationship was robust even when controlling for individual differences in baseline performance. Thus, emotions elicited by social contexts appear to wield power even at the level of perceptual processing.
Most, Steven, and Jean-Philippe Laurenceau. "Blind Jealousy? Romantic Insecurity Increases Emotion-Induced Failures of Visual Perception." Emotion 10.2 (2010). Web. 18 Apr. 2010.

This is interesting because now the phrase "you only see what you want to see" has even more weight.  Yes, the physical reality of the world consists of light, space, matter, etc. and color can be dismissed as a series of photons traveling on some set wavelength.  But what we see, what we actually see can easily be affected by what our brain dictates.  As the functions of our brain and the impulses, ideas, emotions, etc of our mind meld together, our behavior (sight/perception) must change accordingly. 

This question "if the brain imposes its own construction on perception, how much of what we actually see is real (versus "fake" or an "illusion")?" seems to be popular in this forum.  However, I'm beginning to develop a distaste for the label "illusion" or "fake."  I don't think any part of life, generally, is an illusion. People do have different perspectives and backgrounds that help create a range of lenses with which they can experience life.  Maybe in a vacuum, we would and could see the world as it truly is (color as a physical entity). But in this world - our world - where social interaction, social construction, cultural and societal bias is nearly unavoidable, we see color because our brain wills it or constructs it.


link to sciencedaily article.

AndyMittelman's picture

filling in the blanks


            I was particularly fascinated by our discussion of color blindness this week. Like Lauren, I am curious to know more about some of the evolutionary aspects. Is there any advantage to missing certain photoreceptors? Someone mentioned in class that certain people with color blindness are more effective at detecting camouflage. I would be curious to know if there are any “natural” applications of color blindness. Also, how is this manifested in the animal kingdom? I would think that it could be a serious problem for certain wild species. On the other hand, if a certain species existed in a very colorful environment, perhaps an absence of certain photoreceptors would serve as a welcome simplification of their chaotic surroundings.

            We have discussed how our brain “fills in” lapses in sensory perception. If input is blocked (such as by the blind spot in our vision), then our brain can subconsciously plug in what is likely the appropriate missing link. This occurs without our conscious consent. This makes me wonder if our brain could fill in color in the case of color blindness. Is it possible that our brain could recognize certain shades or textures and “color it” such that we perceive color without the appropriate photoreceptors? Theoretically, if we can fill in shades and spots in our blind spot, then maybe we can fill in color as well. Is it possible that we could be color blind and not even know it because our brains are “picking up the slack” of our photoreceptors? This may be an extreme example of what the brain fills in, but it seems clear that our brain does indeed fill in small “blips.” Hence, what is the limit of what our brain could “fill in?” Could our brains be filling in more than we might expect? Maybe we’re not actually “seeing” anything but rather out brains are just filling in everything according to expectations.

            I am very interested by the mechanism through which our body fills in what we don’t actually input from the senses. What is actually going on when we complete the line in the blind spot? Like other bodily mechanisms, can it be impaired/enhanced through substances, disuse, or training?  If it is like the stitch-work that we are doing constantly with our eyes, can it be affected by damage to the nervous system or the brain? I’d be curious to look into how injury affects our ability to piece together missing sensory inputs…maybe a good web paper topic.

dvergara's picture

Recreating the world

There is one idea from class that has really stuck with me when thinking about perception and vision. It is this idea of the function of the lateral inhibition network, that it throws away certain information and then creates a new image, the image of the world that we 'see'. If our nervous system is "creating" a new image, than this image is merely a reflection of the world, very similar to Plato's Cave theory. How then, can we ever determine what is real? Can we even begin to imagine what the world really looks like? 

Plato believed that only through philosophy could we really gain a truer understanding of reality, our seeing the material world was simply not enough. I ask then, by asking these questions of perception and doubting our own reality, are we reaching a truer understanding? I personally doubt we could ever 'see' reality because of the physical limitations of our bodies and nervous systems. It is however interesting that we seem to have come to somewhat of an enlightenment by realizing these limitations, and attempting understand why they exist. If we know our vision is limited by the capacity of our rods and cones, than we can begin to imagine or create a picture of the world that is not limited thus.

egleichman's picture

shying away from nurture

Well I was going to talk about vision, but then I came across this article by LiveScience which seems to shed a new light on human perception:  (  The study suggests that the input/output systems in shy individuals are notably different from that of the extrovert.  One really interesting part of the study found that shy/introverted people may pay closer attention to sensory input, with more activity happening in the part of the brain that sorts stimuli than everyone else; shy/introverted people are, according to the article, more sensitive to loud sounds, caffeine, crowds, and pain.  

Could shyness be so predetermined?  Does this study suggest that a lot of nature, and maybe not so much nurture, play into a person's shyness since it's very much to do with how our brains handle sensory input?  And is the shy person evolutionarily favored because of his inclination to process input more slowly before acting upon it?

Colette's picture

              Our brains


            Our brains create selective senses. The brain regularly chooses what it wants to hear or see and also fills in what it wants to hear or see. As a result, live in illusions. As part of the nervous system the senses physically report their perceptions to the brain. This data like other data in the nervous system is coded in electrical currents. If nothing is transmitted there is no perception. What the brain does with the data may be something else. This creates a large potential detrimental effect on our lives because of misinterpretation of things as they really are. On the other hand, the potential for bad decisions is increased when the decisions are based on incomplete or false data. Life can be more interesting, however because of the variation. For example, we may perceive different shades of colors. Hot pink could actually be light This phenomena could also be very useful in certain situations. For example, when I'm singing in competitions, it's nice to now know that if I do not quite correctly pronounce words in foreign languages, the judge’s brains will hopefully fill in what they think I was supposed to sing. The fact that people find so many ways to perceive things is perfect evidence of how the brain imposes its own construction on perceptions. This leads me to wonder how much of life is actually an illusion.

Congwen Wang's picture

Colors & 3 dimensional vision

I have to say that although I know that we perceive colors differently, at first I didn't want to believe colors are the construction of the brain. I used to think the wavelengths of the photons are the "physical basis" of colors, and our different perception of them is due to the limitation of our body structure. Our last class completely changed my vision. Now I do see the point, and it actually helps me understand the chromatics better. It's fascinating that our eyes can distinguish so many colors.  I do graphic design with computer sometimes, and I know there is a big difference between the color spaces on computer and in print - and the range of colors we can see is much wider than both systems'. People in the color space business are constantly expanding the color space by finding ways to show the colors we have never produced.

I also find the discussion about binocular stereopsis very interesting. My right eye has been shortsighted for a long time, but since my left eye is normal, I don't wear glasses. So I'm actually looking at things with one eye. Somtimes it does affect my sense of space (for example, I can't play badminton because I can't tell the distance very accurately), but for most of the time I'm doing fine. I wonder what the other ways we have to sense the depth. Also, what is the role of our experience in this? 

aeraeber's picture

Reading Between the Lines

People tend to have trouble explaining why they like a particular song or painting. They are hearing or seeing something that is completely unique to them, and certainly isn’t what the artist heard or saw. There are probably common threads; it’s unlikely that one person would see a pink flamingo on a lake where another person would see a black and white map of the London Underground, for example. Still, the vast differences in emotional response to art imply that there are also large differences in perception of it.

The evidence that what we perceive is a construction of the brain rather than an exact representative of an external reality is rather strong. The brain provides multiple interpretations of ambiguous figures, like those in classic optical illusions, and interprets know objects as the same color in different lighting situations. Though it seems strange at first that information gets thrown away before it reaches the brain, it actually makes sense to have a mental picture that is useful rather than completely accurate. If objects and people looked different in changing lighting conditions, it would be impossible to give directions or recognize people from their pictures. What we respond, what determines behavior, isn’t “reality” but the informed guess the unconscious part of our brain makes. This helps explain why people react differently to the same stimuli. The fact that some people are afraid of heights or electric storms while others are fascinated by them may have something to do with the fact that the unconscious parts of their nervous systems make different guesses, so they perceive different things. We’ll never know, of course, exactly what another person is seeing, hearing, etc, but knowing that it isn’t exactly what we perceive is important in interacting effectively with them.  All of this leaves almost as many questions as it provides potential answers. Why are all of our informed guesses so seemingly similar? That is, how are we able to know what someone else is talking about when they describe the world? How did our system of filling in the outlines develop? Is the fact that we don’t easily notice when someone changes something about their appearance, like their hair or glasses, related to our reliance on mental pictures and filling in the lines?


emily's picture

 First off, I just want to

 First off, I just want to say that I love color, it fascinates me. Color vision is something beautiful we often take for granted. I understand how we all have different perceptions of each and every color (from crayon colors cerulean to macaroni-and-cheese), but it is hard for me to believe that people's color concepts vary SO MUCH. For example, I find it hard to believe that someone (who has no form of color blindness)'s "orange" could be my "green" because both of us describe "orange" to be "warm". However, it fascinates me to imagine what someone who is color blind sees as a color they are not capable of seeing. For instance, if they are missing their high range wavelength cones, do they notice a difference when someone else calls something red, and another calls something green? In Little Miss Sunshine, the brother wants to be in the Air Force, which you can't join if you are colorblind. He does not realize he is colorblind until some point on their road trip, which is several years into his life. What did he see?

Another thing that really fascinates me is electronic color. How can you program a computer, a tv, to produce a specific wavelength of light? One often thinks of color (the reflection/absorption of wavelengths) as an intrinsic property of an are those lights created and how can they change?

MEL's picture



I found our discussion about color this week very interesting. I have always wondered about color perception and how it differs from person to person. Although it makes sense to me that every person interprets wavelengths and perceives colors differently, it is still strange that color is completely a construction of the brain. Is our individual color perception due to genetic factors? Is my perception of the color red similar to my mother’s perception of red? Is there any way to determine how two people’s perceptions of a color differ?  Our discussion about color got my thinking about the consequences of people having different color perception. What influences color pairing? For example, when I pick out an outfit I usually try to avoid some color pairings (purple and yellow) because I think they clash. Most people agree with the opinion that purple and yellow clash. How does this conformity develop if we all see different colors that correspond with the names “purple” and “yellow”? Is this conformity due to environmental factors? Are many people taught that certain colors don’t match and then, therefore, internalize the belief that the colors that they perceive, such  as “purple” and “yellow”, do indeed clash? How do we form color or color pairing preferences?


Lauren McD's picture


I really enjoyed discussing vision this week in class, as it's something that we all take for granted without truly understanding it. The most interesting aspect of vision that we touched upon this week for me was the topic of color. It's interesting that color is not a physical property of the world, but instead a construction of the brain. This idea has plenty of examples that help support its statement. Dogs don't see in color, but humans do. Therefore, there must be some physical difference between dogs and humans in the brain that allows only us to see color. Also, in a dark room, it is impossible to distinguish different colors because no there is no light to reflect off the objects. This is a counterintuitive idea, but an easy one to understand because of the many examples in everyday life. We talked in class about how we only see color if our cone system is activated. I remember doing an experiment in high school biology in which an object was put in an observer's periphery vision, and the observer stated whether he saw the color first or the shape of the object first. I don't remember the outcome of the experiment, but either outcome would suggest that cones are more densely compacted in one area of the eye and rods in another. Is there some sort of evolutionary advantage to this? I found it truly interesting that we analyzed how we 'see' color, and I look forward to analyzing other senses.

Jeanette Bates's picture

Color Interpretation

I am not at all surprised to learn that our individual perceptions of the world are constructions of our unique brains. If there was only one truth that could be seen or only one way to interpret it, then everyone would probably perceive things the exact same way…which would be rather boring. In a sense, I think that there are many truths, or many near-truths. There isn’t just one way to see the world, there are many ways, and they are all valid interpretations. I am pretty convinced that at least part of the reason why people can have such starkly different opinions about the same thing, like a piece of art, is because they actually see something completely different from what the other person sees. Perhaps if someone saw the picture that another person constructed in his or her brain, then that person might agree with the other person’s opinion. I think that this notion, that people see things differently, could apply to how people, and not just colorblind people, see color. For example, my friend likes the color orange, but I think that it's rather annoying. My orange is different from her orange, and so we have different opinions about it. We don’t see the same thing, and to be honest, I like that. If there weren’t differences like these, life would get boring pretty fast.  

mcurrie's picture

CPG's, Corollary Discharge, and the Eye

 Talking about the eye I felt frustrated, I understand the eye, I understand it is important that we get a lot of sensory input from the eye. When talking about the eye I wanted to connect what we had learned so far about corollary discharge and central pattern generators, refractory loops, etc. to understand how the signals from the eye were used with the other parts of the brain. As we kept talking about the brain making a picture, making deductions, is this because of corollary discharge or is it more through the I-function? How do central pattern generators fit into the information we have discussed about the eye? I figure we would have a CPG for blinking, but what else? Could you have a CPG for colors and the names that go with the color you see? I know that when a person asks about what colors I'm seeing I use the words that were told to me by my parents and teachers. Then when I was able to read I would look at the crayons and read what color the crayon was. Did I form a CPG or amount of neurons that I use day to day to figure what colors I am seeing, or was the CPG always in my brain that recognizes the signals from colors and I just added on names. Does this even make sense? Is it right? I know that behavior can be greatly influenced by the eye, by the sensory input, like when I see an object flying at my face I will try to protect my face by lifting my arm. There is a connection between the eye and a CPG of movement of my arm. I feel that I am ready to explore more of these connections with what we first discussed and how to connect what we discussed about the eye to then figure out behavior. I'm ready.

molivares's picture

Color Plays Musical Chairs In The Brain

In class we have mainly been focusing on the structure and anatomy that are needed to see and perceive the world. We’ve discussed photoreceptors and their role in color blindness but to take things a step further, how is color perceived in the brain? I found this interesting article Color Plays Musical Chairs In The Brain that I thought was really interesting. We certainly attribute particular colors to particular objects but this article explains how features of the object (i.e. its shape, color, size, location) are represented in different parts of the brain. The brain then pieces all these features together so that they makes sense to us. The article mentions this as a sort of “neural gluing.” What this study looks at is what happens when color loses the object to which it is linked? It showed is that for the first time, that instead of disappearing along with the lost object, the color latches onto a region of some other object in view proving the idea of neural binding or neural gluing, where the color is connected to the object in an active neural process.


mcchen's picture

Color as a construction of the brain

 This week we started talking about color and how the way we perceive colors is all a construction of the brain.  This made me think of the countless number of times I have argued with my friends and family over the certain hue of a particular object.  So an object that I perceived as teal, so more of a blue-green, was just plain green to someone else.  I always thought the way I perceived the color was correct and didn't understand why we all saw colors differently.  Now I understand that our brains all perceive color differently and the "maximum" peaks in our photoreceptors may shift slightly from person to person.  Therefore, my brain may discriminate between more heavily between two colors than someone else's brain.  I know now that the color argument is not worth pursuing because we all have different views of colors and that should be appreciated rather than fought over.  It is interesting that something like color is a construction of the brain just like how opinions and ideas are a construction of the brain and they all vary from person to person. 

gloudon's picture

color blindness in women

 In class we talked about color blindness.  I read that color blindness is much more prevalent in men than it is women, because the gene is carried on the X chromosome.  It makes sense to me that if I women had one X chromosome with the color blind gene, that the non-affected chromosome would dictate control of the formation of cones in the eyes.  7% of males in the US are color blind, however only 0.4% of women are colorblind.  Do these 0.4% of women carry the color blindness gene on both of their X chromosomes?  If they only carried one, how would that mutated chromosome gain control and mess up the cones and or the pigmentation in the eyes when a normal X chromosome is present?