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An ongoing conversation on brain and behavior, associated with Biology 202, spring, 1998, at Bryn Mawr College. Student responses to weekly lecture/discussions and topics.
What general lessons about perception and behavior generally come from considerations of the blindspot of the eye and/or from discussions of how a two-dimensional retinal image is transformed by the brain into a three-dimensional perception?
Your last lectures made more of an impact with me (than it did in lib. studies) having an understanding of the I-function. Your description of what we are seeing being all in our I-function, makes sense in this context. I wonder why if it is all in our mind, we can not command what we want to see at will. There are only a few conditions in which you can: under the influence of drugs, having had a brain injury, in a sensory deprivation tank, and with a chemical imbalance in the brain, etc. There was a man in one of the books I read last year (from lib. studies) that would see his old village (Pontito?) at random times. But it would be from different perspectives and from distances that he had never seen it from. He could see it and travel where ever he wanted to go in the vision at will. He also was not fully living with us in the present world, he seemed to be mostly stuck in the past and sensing things as if he were there.
Another example is that under the influence of certain psychoactive drugs visions and hallucinations (things that are not part of our usual reality) can be seen, I do not know if they can be manipulated at will. The accounts of people that have been in a sensory deprivation tank are very interesting. These people are not on drugs, are physically healthy, and otherwise normal yet when not presented with any stimulus, the brain/mind/whatever has the power to produce anything that the subject wants to see. The person can manipulate and produce whatever they see fit. It seems as if because of the lack of sensory input, the mind makes up something. Which it does all of the time in our blind spots. In addition, when it is dark and our eyes do not receive as much light, we tend to see things differently. I remember that when I was younger I saw a giant dark figure in my room when I focused on it I realized that a giant Strawberry Shortcake was in my room menacing in front of me. Of course, I finally realized that it was only a funny shaped shadow.
All of us dream and in our dreams visual images are seen though none are actual. The body does not receive visual information and at that state we are able to create our own. In some cases we combine the information. I remember having a radio come on while I was dreaming, I experienced the music and the dialog that was going on in my dream. The other day Eliza and I were discussing imagination. Even though we could imagine seeing each other with a blond wig on, it was not the same as seeing the blond wig on. It is almost as if the image that we want to see is superimposed over the image we are seeing. The experiment of holding our hand in front of one of our eyes gives us a similar reaction, we see our hand and what we were viewing at the same time. In both cases the brain gets two different images and then combines them. However, the hand experiment is a little bit more realistic then the imaginative one. Though, for some (young kids ond older ones) their imaginations are close to reality.
Maybe it just helps to visit and revisit? Regardless, you've certainly not only understood what I'm thinking but added wonderfully from your own experiences and thoughts. Thanks, for both. You've raised a very interesting new issue: when we can and cannot "command what we want to see at will". I'm not sure we actually do "command" in most of the cases you mention (brain damage, drugs, deprivation tanks), at least not if you mean that the "I-function" can control what is seen. In such cases, what is seen is dramatically (more so than in normal vision, but the difference may be quantitative rather than qualitative, for reasons we've talked about in class) made up by the brain (as opposed to what's "out there"). But its not really "controllable" by YOU. The "giant strawberry" is interesting in this connection, since you actually did influence what you saw, yes? We'll come back to this ... and to the issue of the relation between imagination and reality. PG
It's apparant that some portion of the brain is responsible for filling in the gaps in our perception, such as the example made in class of the blind spot. It's amazing that the brain has this "sense" function, that makes everything make sense despite shortcomings in perception. But sometimes, it gets it wrong.
Apparantly the mind's eye is not always under the control of the I-function. For example, in synesthesia, images will be "projected" in front of a person's eyes involuntarily. And in the Scientific American article on our reading list about Phantom Limbs, there's a section about phantom vision and hearing. People who are gradually losing their sight may have clear images projected into their blurry field of vision. The example given was that a woman suffering from a cataract happened to glance out a window into a field which she knew from experience was empty. She was astonished to "see" a building there. Though her vision was not acute enough to see objects at that distance, the house her brain made up was very clear. The vision disappeared several hours later.
Is this latter example a case of the brain goofing when it manipulates the data to make things make sense? What is the function or benefit of this? It seems like a disadvantage, if you lived during witch burning times.
Ordinarily the brain might produce images according to what's on your mind, making you think for a split second you see something you've been thinking about. Or objects that haven't been clearly viewed yet might be misinterpreted in the brain's attempt to have an evaluation of what they are. Images on the periphery of a person's vision tend to get this treatment-- I set down a yellow apple on the dining hall table the other day, and startled my friend, who thought she saw a rubber duckie. It's another case of the brain reaching a rather farfetched conclusion in the effort to make sense, and just making things more confusing.
Enjoyed the rubber ducky, suspect others will as well. Thanks. Why does the brain do things this way? Is it just "goofing up", a disadvantage, a gummed up system? It can certainly look like it if you have in mind that there is a "reality" out there and that its the brain's job to "tell you about it". But how about trying to look at things from the brain's point of view? What is IT dealing with? Maybe just a lot of action potentials which it is trying "to make sense of" as best it can (and, perhaps, as quickly as it can)? Looked at that way, maybe the brain is doing a remarkably good job? And maybe there are even some "benefits" in all this? My guess is that witches were burned because non-witches were afraid that the witches could actually see "better" than they could. Can you imagine any ways that "goofing up" might contribute to that? PG
Most interesting was what we learned about depth perception and binocular vision. As an infant I had crossed eyes and underwent surgery to correct this, however my right eye is not as well utilized as my left. Actually, I get very little information at all in my general view of the world from my right eye. For the second web paper I have decided to write on this topic, more specifically, strabismus and amblyopia, which is misaligned eyes, and having one eye that does not see as well as the other.
One major ting I notice about this funny condition is that perceiving depth has always been hard, but only in certain situations. So, learning about depth perception this week was nice. For example, I can catch a Frisbee and drive a car, but pouring water from a pitcher into a glass is very difficult. The only way I can do this with out making a mess is if I am off the horizontal plane with the glass, but in low light, like that in restaurants I still have a hard time. Another time when the problem arises is on dark and stormy nights when I am driving. The low light, low numbers of peripheral cues make detecting depth extra challenging.
When these situations arise I get very agitated, and I often don't know why. It is really weird, because I can see just fine usually. My one good left eye is able to detect depth just fine most of the time. My brain seems to be able to define depth all right just when there are tough situations it can't. Can most people pour a glass of water with one eye closed in low light?
Another result of this eye thing is that my right eye will wander about, looking around at things that I, my I function, never see! This happens really only when I am tired or feeling ill. But when it does I don't know about it, my brain image does not double or get skewed in any way. It is as if the brain is turning off that eye. In its interpretations of the signals coming from the eye nerves it chooses not to look at those from my right eye.
I have found many good web sites on this problem and will write more in the web paper!
Very much looking forward to the paper. And thanks for the direct observational evidence along the lines of what we were talking about in class. Interested in pouring under low light on horizontal, since I too had mildly wandering eyes as a kid. Will try it (though probably at home instead of in restaurant). May have to do with something more complicated/interesting than simple absence of stereopsis. Yes, brains do, under varying circumstances, more or less ignore signals coming from one eye (or other sources). PG
I also thought immediately about dreaming as "proof" that the brain's perception is pulling 2D images off the retina and making them 3D. My eyes are not built to see much of what is going on, but my dreams are clear and very 3-dimensional. In my dreams, I am able to see much more than my retinas are shaped to see. The explanation for this may be very simple. Most of my vision during the day is corrected and (I am assuming here) dreams come largely from daily experiences that I see through contact lenses. This may account for the clarity of my dreams. In order for anybody to dream, then, like in the images that we all have in our heads, the brain must be pulling information off of the retina and transforming it into a 3-dimensional movie.
An aside: Where I worked as a Peace Corps volunteer in Africa, women would consult the Nganga (traditional healer) and ingest a hallucinogenic root (Iboga) in order to "dream" in their own minds' eye the story of the theft of their big pot or whatever stolen object brings them to the Nganga. In their heads, they could live the entire story from start to finish and could stop and start the story where they wanted. While we haven't discussed the effects of hallucinogens on the nervous system, I find it interesting that so many people would see the running of a film that may or may not be true to life through our heads (and eyes) as magic. Really, our brains are doing it every day.
Yes, indeed, our brains are doing it every day. Good point (from which it maybe also follows that, in some profound sense, it is indeed "always about me"?). We'll get to hallucinogens. In the meanwhile, your thought about 3-D dreams is very interesting from some addtional points of view. Have you had blobby vision all your life? When was it corrected? There are interesting issues having to do both with the origins of 3D concepts and with the parts of the brain involved in "seeing" (in waking sense) as opposed to "dreaming". PG
More generally, the fact that the brain turns inverted object images within the eye upright and also makes 2-D images into 3-D pictures makes much sense. After all, isn't the human body all about the modifications of mechanical flaws of one organ by another? This is all a question of survival and how, if the brain did not perform the necessary visual adjustments it did, we as human beings would simply cease to be a successful species. Indeed, perhaps the growth and specification/diversification of the brain has to do with something that is illustrated by this optical example. Perhaps the growth of the brain depends on what it can "fix" and what it cannot "fix." Perhaps this massive neural structure feeds on an ability to take the disadvantages of our physical components and turn them into psychological advantages. Just food for (and excuse the pun) thought.
Punny. And an interesting set of thoughts in all that. I'm not sure that the brain knows what "necessary visual adjustments" are or what is "flawed", but it is certainly true that there are continuing adjustments of parts of the body and parts of the brain all to each other. Which, of course, makes it harder to specify exactly what the "function" is of any part, but may also help to explain why the system has the adaptive flexibility it has. PG
For some reason, I immediately thought of children with bad eyesight that are not able to communicate this to their parents, or the poverty-stricken who are not able to obtain corrective eyewear. I cannot help but think that these groups are placed at such a disadvantage because our eyes are such a powerful source of information to our brain about our surroundings. I think that it is so important to support charities that supply corrective eyewear to those who are not able to afford it and to also be sure that our children are seeing adequately. It also made me wonder how infants' vision is checked?
Now, onto the actual topic!!! I have been fascinated by how much the brain compensates for deficiencies in our vision caused by the blind spot. To think that without this input by the brain that we would be seeing a significantly large black hole in our vision is an interesting concept to think about.
Furthermore, I was struck at how readily these deficiencies were apparent when we simply closed one eye. It is obvious that the eyes were meant to work as a team - together sending input to the brain, and when it is conflicting, the brain simply takes over, supplying the necessary information to not cause a huge deficiency in the world that we "see."
I have certainly enjoyed this topic and had NO idea how much of what I am seeing is what my brain is actually WANTING me to see!!!
"Causing" may be better than "wanting", since you at least didn't even know it was happening. And I very much agree with your point/concern about kids/others who may not be aware that problems they are having are correctable, may not even know why they are uncomfortable. Is interesting, in fact, to wonder what behaviors being uncomfortable for such a reason might in turn cause. PG
May actually even be that is isn't even very much due to the "I-function", huh? Is good point, and does in many ways make it easier to approach the question of what actually does influence what we see, to recognize how many influences there are in a situation which otherwise seems so obvious. I ought to be able to think of an explicit test and can't at the moment, but my bet is that things are seen even when there are no variations in light level whatsoever. PG
We'll talk about the I-function/consciousness in relation to visual perception (as we did with motor control). For the moment, its worth pointing out that lots of the things we've seen are happening (the filling in, for example) happen without the I-function knowing about it (at least until recently), much less controlling it. So we don't have to worry about the vaguely defined I-function for that part at least. "Objectified", "personally processed" by neurons? Not sure exactly what you mean, but remember that neurons are nothing more (and nothing less) than those cells we talked about at the beginning of the semester: all they "know" or do is in terms of permeabilities, current flows, and membrane potentials. PG
His computer had a program called director that allowed him to alter things in such a remarkable way. He said that when he hooked the VCR up and ran it through the program so that it split the images, he could watch movies in 3-d. In one of his examples that he used for classes, both eyes got the same shape but in different colors. Both eyes would fight for dominance and the colors would move back and forth. Or, one eye would be dominant and only one color would be seen. Sometimes the image simply looked iridescent, he called this luminance. He thought that the same thing occurred in nature, each eye gets a different color and it looks iridescent or "luminant (is that a word?)". As we moved around the room, the images also moved. If there was a tree behind the house, he had no way of displaying the hidden information that would be revealed by walking to the side. As a result, the background items slid horizontally as we moved side to side. If we tilted our heads too far to the side, we would see the image as if we were not wearing the glasses. This is because, at that angle the glasses could no longer receive the polarized light.
Speaking of interesting speakers, at church today I was reminded of the neural maps that we are all born with and the phantom limb phenomenon. It reminded me of how God has a perfect way that he wants the world to be in and a perfect relationship that he wants with us. And, how we all have this understanding (neural map) in us. However, when our actions or what we see happening in the word conflict with this, we feel pain. When we ignore the relationship with God and behave as if he is not there, we feel a ghostly longing or pain, as the body feels when the limb is gone. When the internal image conflicts with the external, the ghost limb phenomenon is experienced. When we have all of our limbs and have that perfect relationship with all of body parts functioning together we are complete and fully able to live. When we are not in that perfect relationship with God, we are not fully and freely living. When we do have everything connected and working together we truly have no pain (however, the perfect relationship with God only occurs in heaven (we get glimpses of it), unless you are Jesus). This is not to say that with God once a limb is gone, it's gone for good (this is only a metaphor). Anyway, I'm constantly being reminded by this course of the goodness of God and how remarkable God is.
You've had an active week (see above). Thanks for both reports. The 3-D talk sounds wonderful, and the metaphoric parallels are very interesting/intriguing. PG
I understand the sense of resignation - "does not make the account of our visual faculties more rosy". But there are some more optimistic ways to look at it. At a minimum, one might say that the more one knows about the specifics of "limitations", the more one can do to transcend them. Knowing that there are wavelengths of light which we don't see, it became possible to design instruments that bring awareness of them into our realm. More generally, and abstractly, "limitations" is meaningful only if one presumes there is some perfection which we need to discover and to which we should aspire. An alternate perspective perspective is that it really IS true that, at least in some senses, we ARE making up "reality" as we go along. Is that make what we do "rosier"? PG
I think this technique will dramatically increase the databse researchers have on the brain right now. Before, the only way to study the brain activity was to do autopsies on partients with known neurological problems or by coaxing animals to do simple tasks and then recording their brain activity with an electrode. Not only will researchers be able to study more basic brain activities now, the research will turn out much faster- instead of speding one year on a smidgen of brain activity, the fMRI will be able to record a de image of the entire brain in three hours.
I wonder if using the fMRI will lead to finding new integral areas of the brain, such as finding out exactly where the I-function box is. This should be possible because the IBox would be an area under constant activity so it would always be highlighted in the resulting scans. It would not be highlighted if the person feels they do not have control over their body function. If nothing else, the new MRI will be able to help map each activities corresponding area of the brain.
Yes, indeed, new imaging techniques are making it possible to see things never seen before, These include the things (patterns of activity, in our terms) which go on between input and output and, maybe even more important, the things (thoughts as patterns of activity?) which go on in the absence of input and output. There are still significant limitations (as with any technology), in terms of resolution both in space and time, but these are getting less so. More importantly, it remains essential to have useful ways to ask and answer relevant questions. Even if one could see everything, it will look like an indecipherable complexly changing set of colors unless one has some sense of what one is looking for. And the space/time issue may remain critical, no matter how good the resolution gets. I like your idea of finding where the I-function box is (and had an imaginary experiment of my own along these lines years ago, involving more primitive imagining technology). But what if that "box" isn't a particular "place" but rather a particular form of interaction of lots of places (like an output is not a particular motoneuron but rather a pattern of activity across lots of motoneurons, each of which is also involved in other outputs)? Then it might not be easily detectable (detectable at all?) in brain images? PG
I find it incredibly interesting how little control we have over our vision --what a small part, if any part at all, the I-function plays in what we see. Hmm... Well...let me modify. We have absolutely no control over the light that falls onto the retina. However, I do--I think--I do believe that the I-function plays a part in the interpretation of what we see--which results in the brain's final perception of the image. I think it must be the I-function that sorts through the myriads and myriads of information constantly entering the brain through our eyes(and other senses). For instance, when we look at, for instance, a room---all the light bouncing off all of the objects and patterns and pictures will enter the eye and find paths into our brains. What we may actually end up perceiving is a bed, a chair and a lamp, but what we may not notice is the run of the grain in the wood of the chair or the colour of the ends of the petals on the flowers of the bedspread--those details aren't important at a first glance. Now we can CHOOSE to notice those details and remark upon them. Does this make any sense? I fear I may be confused on this issue. I guess what I'm suggesting is that the image that enters into the brain initially is absolutely rich with images and colours and an overload of perceptions, and perhaps it is the job of the I-function in this case to sort through those overwhelming images to focus on a clear image that we can hold in our mind and understand.
Yes, you're making sense. And we'll talk more about things related to your intuitions. Yes, its true (as we've seen) that there are lots of possible interpretations of the input. What's probably also true, for reasons we're currently talking about and will keep talking about, is that much of what you call "sorting through" is actually not done by the I-function, which instead is usually offered an already sorted through product. But, as you say, it is then possible for the I-function to allow/encourage/request reexamination, which results in a new or more precise or more something else product. PG
A little late, but in response to negative feedback loops... the idea of bi-directionality in relation to motor control sparked a question in me that I think someone may have asked in class. We were discussing that the set point within our bodies can be changed as an effect of gamma motor neurons. I was wondering what kinds of changes in activity within the nervous system correspond to the set point.
After being struck with this question, I was recently reading a biology book and think I may have come across at least part of the answer. The hypothalamus is the body's thermostat and contains sensory nerve cells. When an invading organism enters the body, the set point is raised in order to fight the bacteria better. The increase in temperature results from the white blood cells that respond to the infection, releasing hormones. They travel to the hypothalamus which results in an increase in the set point. Now, since your body is associating it with being too cold, it tries to raise the temperature more by shivering.
This is probably a terse explanation of a very complicated process. Would you happen to know more about this?
Actually, I don't. But you're doing pretty well exploring the issue on your own (doing so, less tersely, might make an interesting web project). One obvious issue worth looking into more is what actually happens to neurons that corresponds to "an increase in the set point". It could be greater firing frequency in neurons, or more neurons firing, or ... ? In the case of the muscle feedback loop, it corresponds to shortening of the intrafusal muscle fibers. PG
The blind spot in our eyes cause dilemmas for anyone who actually sits and thinks about it. We know that each eye sees what the other doesn't, so we never actually know where our blind spot is when we look at things in the world. It is a bit distressing knowing that we don't actually "see" part of what we think we do.
I tried the experiment from serendip that you suggested and was wondering if this is what is supposed to happen: I allowed a pencil to approach the blind spot and before it completely passed through the spot, the pencil tip seemed to disappear. Once it came out the other side of the spot, the entire pencil reappeared. The middle portion was visible while still located in the blind spot. The brain is filling this part in, but only moments before, the brain was unable to make sense out of only the end of the pencil and wasn't able to complete the other part of it. Without cues from our surrounding, it must be difficult for the brain to "fill things in" in order for the world to make sense.
In one of the other experiments, there was one yellow dot surrounded by many red dots. Since our brain used the surrounding background information, it unknowingly placed an incorrect colored red dot in the yellow dots place when that region was in the blind spot. I am just curious about what the brain would do if there were random colored dots all around, so there is no general pattern for it to follow. What color would the brain select to fill in the specific region?
There isn't, of course, any "supposed to happen". Different people might be expected to have different experiences, and do. On the other hand, I and most people that I've heard from, report pretty much the experiences you're reporting. Your question about randomly colored dots is a wonderful one (and closely related to a question from a student several years ago which triggered the whole serendip exhibit). You can try it yourself with a piece of paper stuck to the wall. Let me know what you experience ... and if you think its worth it we can make one for serendip (let me know if you want to help). PG
In light of this, it doesn't surprise me that the brain accomadates for the blindspot on the retinal image. Honestly, I've passed the point of surprise in this class. I wouldn't expect anything less out of such an extraordinary system as the nrevous system. In this sense then, blindspot accomadation is an example of a general property of the brain. This property might be called "unconscious integration". We have often seen examples of the nervous system working on it's own and doing things that we are unaware of. Examples of this are central pattern generation and corallary discharge. I would argue that blindspot accomadation is very similiar to these other phenomena. I think is is this "unconscious integration" property of the brain that causes me to skake my head in wonder in class. Our nervous systems allow us (humans) to be one of the most complex organisms around, and I think it's because it does so many things without our being conscious of them.
Sorry that this got to be so incoherent and rambling, but it is really hard to articulate the ideas I want to convey. But I'm sure that I'll get it eventually if I keep trying.
I'll leave it to others to pass their own judgements, but I think you're pretty close to saying very clearly what you want to say. Yes, indeed, our nervous systems do an enormous amount (and "know" a lot of things) without our being aware of it consciously. Which is very much the point of what we've been talking about (along with the idea that there isn't anything mysterious, only unconscious, about how it does this things). PG
Also it was interesting how the brain may perceive depth from corollary discharges indicating how the muscles attached to the lens control its curvature to focus on far objects as opposed to near objects. My father has artificial lenses in his eyes due to cataract surgery, and he says that sometimes his depth perception seems a little altered. Maybe this is because the artificial lenses can't be controlled by the muscles as well as natural lenses? Since I know the muscles controlling the lens weaken with age, would older people have less depth perception than younger people, then?
I was relieved to find that I'm not the only one who can't see the 3-D images in "Magic Eye" posters. However I have a related experience in regard to pictures that contain "hidden objects" in the scene, for example in Highlights, a kid's magazine. These pictures were very interesting because at first I couldn't see the objects and it would take a lot of concentration to find them, but once I had identified them I couldn't go back to not seeing the objects. Also once in a high school art class the teacher made us sketch a slide of a painting that she first kept out of focus and then slowly brought into focus. Soon we were surprised to find that the picture we'd taken such care to draw was actually upside down. She said this exercise was to make us draw what we were really seeing, not what we thought we were seeing. I wasn't sure what that meant then but now I think I do.
I'll end this with a question anyone is free to answer (though I'd like Prof. Grobstein's input, too). How can you explain, in neurobiological terms, why some people have much worse hand-eye coordination than others? For example I find it very difficult to put on makeup, or serve a ball from a raquet. Does this mean my NS isn't as good at coordinating the corollary discharges from different parts of my body as other people?
Very interesting set of thoughts/connections extending with concretes important ideas we've been talking about, and raise appropriate new questions. Many thanks. I'd never thought, for example, about cataract surgery, but presume that the implanted lens aren't adjustable by the nerovus system, and so would guess that yes, one might under some circumstances experience depth perception problems. As for hand/eye coordination, I've been thinking on and off about that as I watch with amazement (and enjoyment) things that Michael Jordan does (which, I'm increasingly convinced, neither I nor most other people can do). Yes, how well the nervous system handles corollary discharge information could certainly contribute to differences among people. So too could the richness of that information, or of sensory information. So too could the flexibility of the motor system, in terms of the number of alternate motor programs it can come up with to try out. It would be an interesting exercise to try and list all the possibilities, and then to come up with observations that could be used to distinguish among them. PG
When I was a kid, there was a neat trick we would do - close one eye and try to make two pencil points touch. It was very rare if someone could do it - in fact, we usually found that the points were really quite far away - what a sense of depth perception we have with one eye!
This makes me think of my boyfriend, who has amblyopia in his left eye. Those red and blue 3-D glasses do absolutely nothing for him (but make things all weird colors), he can't see those hidden 3-D pictures that were so cool a few years back... and he compensates for some loss of depth perception by moving around and using different vantage points.
Depth perception = two eyes = two vantage points = discrepancy = depth!?
Another thought which has been puzzling me is - why would the brain fill in that blind spot? Evolutionarily, it doesn't seem to make sense to me. I guess a big black spot in the field of vision would be somewhat distracting, but if there were potential predators in our blind spot, wouldn't we want to know exactly where our disadvantage is so we aren't misled into thinking all is well when really we're unaware how defenseless we are in a region of our vision? It'd be too easy to think we're "seeing" plain grass to our side, when really there's a little critter (read: dinner) sitting in our blind spot. If there were that big black hole, we'd know to keep turning our heads to find it.So, why does the brain put forth the effort and purposely mislead us? (though this gets into the question of whether evolution really has a purpose or direction - another course altogether...)
Evolution clearly has a direction ... toward more "complexity". Like a negative feedback loop has a direction ... back toward the set point. Like a positive feedback loop has a direction ... toward an extreme value. Does that mean it has a "purpose"? In the sense of there being someone who designed the system with that purpose in mind? All one can usefully say is that there exists systems which display purpose in their behavior without their having been a designer ... and evolution could well be one.
Sorry, you distracted me. Yeah, you can look in more detail into that question in other courses. Back to the main points. Yes, "moving around and using different vantage points" is another way to observe discrepancies (try it yourself) and hence get depth cues. Ever watch a cat or squirrel deciding whether to jump from one branch to another? As for the blind spot, my guess is that there isn't much selection pressure one way or another with regard to the blindspot, that the "filling in" there is a reflection of a more general strategy that the brain uses (and hence has been "selected for"), with the blindspot filling in being a relatively minor consequence (though a convenient one for teaching purposes). PG
Another issue that I find to be quite interesting concerning the nervous system, the I-function, and seeing is what role each of these play in hallucinations that one may have. When someone hallucinates something but knows its not really there the I suppose the brain is "creating" an image for a person to see. The case is quite different when a person sees something that is not really there, but believes it is. Is the I-function "causing"(?) "allowing"(?) a person to both believe that the image is there and "create" the image? What is going on in the brain that "causes" the person to actually believe the image is really there?
Interesting and appropriate issues/concerns. Clearly, personal experience and past sensory input affect to some extent what one sees (see the "rubber duckie" example above). And yes, there is some kind of interesting relation between the "making up" which goes on in "normal" vision and hallucinations. If both are (as they probably both are) simply patterns of activity in neurons, what is it that distinguishes a picture of the kind we normally see and a picture of the kind that occurs in hallucinations? My guess is that the "I-function" no more "causes" the hallucination than it does the "normal" picture (since in neither case does one feel a sense of control over it). And perhaps the question isn't so much what causes a person to believe a hallucinated image is really there in comparison to a "normal" image, but rather what allows one to make any kind of distinction between them at all? PG
However, Meredith's rubber duckie anecdote also illustrates the fact that our thoughts influence our perception even in situations with standard sensory input. In my own life, I have noticed that similar "hallucinations" of mine take place much more frequently when I am sleepy or otherwise exhausted.
Thus, it seems to me that "normal vision" is a conscious process of suppressing these thoughts, which are expressed as what we call "hallucinations." We need to be able to make up some stuff, like what fills in the blind spots, but when our body is too tired to control just how much we make up, we can begin to have trouble. Suppressing this imagination, which runs free in our dreams, and often under the influence of recreational drugs, is important to navigating the material world.
Perhaps this accounts for some of the correlation between the drug use and/or mental illness of so many of the artists who have created startling images of our world.
I like your suggestion that "normal vision" may not be opposed to hallucinations so much as what is left over when other stuff (which would be hallucinations) are largely suppressed. It certainly fits the description of your own experiences (which are, I suspect, not uncommon), and the sensory deprivation experiments. If one wants to further explore this, there are some obvious questions. What is doing the suppressing? and how? and why? What is the relation between signals in the optic nerve and the things either created or suppressed? Well worth thinking more along these lines to see what one comes up with. The issue of the relation between mental illness and creativity is one that a variety of people have written about (see Creativity and psychopathology) without a clear consensusm but certainly also worth exploring further. PG
Let me use a specific example. One of the bits of evidence cited by people who want the world to believe that the holocaust never happened is the discrepancies between the memories given in testimony of survivors. If survivor A remembers Buchenwald as having six smokestacks and survivor B remembers is as having seven, then one of the survivors must be lying. Since there is no way to determine which of them is lying, an inverted logic posits them both as lying.
Another example is a courtroom where one witness remembers a criminal wearing a blue T-shirt and another remembers him or her in red. Is one of them lying? Is one of them misremembering? Is either of their testimony reliable if it doesn't agree?
It seems to me that the mind can usually be depended upon to create a reasonably accurate impression of things but not to remember a lot of the details. I have spent several hours in PSB 229 and I still cannot reliably recall the color of the carpet, or the topic of the posters on the wall. If an urgent public defender pleaded with me to remember, would I be able to? Or would my mind in its ability to imagine and unbeknownst to me flip through all of the reasonable possibilities until it hit on one which resonated for some reason and then report the details of that image to both my ifxn and the public defender as a newly recalled memory? Is this what happens when the blindspot is filled in?
I have more questions than comments this week.
Is all right, are good and appropriate questions carrying blindspot implications into a wider realm. Appropriately, I think. Memory is, apparently, a lot like perception itself, in that there is "a lot of educated conjecture". And this does indeed raise interesting issues for the validity of "eye witness testimony" and the significance of conflicts. How does the brain itself deal with the problem of questions of validity of its own pictures? and how might this be extended to the courtroom environment? PG
This last point makes me think about an assignment we were given in my acting class early this semester (one which, incidentally, I found very frustrating): the task was to drink a cup of warm tea, paying close attention to the various sensations which accompanied the action--taste, texture, temperature, etc. We were then to take a cup of room-temperature water and try to "relive" the tea-drinking experience, i.e., convince ourselves that we were drinking tea. Though I failed miserably, some people were quite successful.
Our instructor called this an exercise in "sensory memory", and I suddenly find that this concept is rather pertinent to our current discussions. I don't know if this is the case, but it seems plausible to me that the gap-filling carried out by our brains is related to such a sensory database; perhaps the things we actually do perceive from the external environment provide cues or triggers to certain neural circuits established at some previous point in time? And yet, there must be a much faster and more flexible system than that, because we never "see" our blindspots, no matter whether the thing we are looking at is familiar or not. Alternatively, then, perhaps it is the information gathered from surrounding photoreceptors which allows the gaps to be filled...but still, memory, in the form of established neural circuits, must be involved in recognition and interpretation of photosignals. I am reminded of Oliver Sacks' account of a middle-aged man who had lost his eyesight at an early age and who, upon receiving surgical treatment later in life, was unable to interpret the visual cues his eyes were receiving. Sacks' point was that seeing (i.e., making sense of visual stimuli) is learned, an acquired ability.
I am clearly getting lost here. The point I was driving at earlier, though, was that the set-up of our brains, the ways in which sensory input is processed and modified, allows us to relive experiences inside our brains (memories, dreams, ...), experience things which are "not real" (those funky posters you stare at), and influences motor outputs, as well (e.g., being able to reach out and grab the cup). In short, an understanding of the sensory side is crucial to understanding behavior as a whole.
Yeah, yeah, the sensory side is important (as is the motor side). But there was something earlier that you were reaching for, something about a "sensory memory", or "sensory database". No, WE don't see our blindspots, but maybe other parts of our nervous systems do, in some sense, and cover it up before reporting it to the us part? They might use a variety of different things to "fill in", no? Oliver Sack's example (in Anthropologist From Mars, right?) is an interesting case, about which your thoughts made me think of a new question. Certainly the "I-function" part of the painter's nervous system was confused. I wonder if other parts were or not? Arguably, what needs to be learned has specifically to do with the I-function? Maybe the rest of the nervous system simply stopped "filling things in", and that was what was confusing to the I-function? PG
However, I think that the really interesting idea concerns what happens to the information that we get from the rest of the NS in the form of negative feedback loops. How reliable is this information? It seems that if the brain can alter the information that comes into the NS from the outside, it should be able to alter information that comes from other parts of the NS. So I guess this leads to the question of how much we can trust our own brains. This basically shows that what is out there and inside us is all a creation of the brain.
A very interesting extension, both information about the world and information about the self is uncertain, yes? So, how do we deal with that? What should we, the nervous system do? That's a subject to come back to. As is color. PG
Another question that came to mind after this weeks class was "is what we see really what is out there?". This is not a question of the existence of truth and I am not trying to say an object only exist if we think it does, rather what I wonder is what is there that we don't see. For example fish can "see" the electrical fields that surround all living things and by perceiving changes in the electrical fields they can locate objects. Some birds have shown the ability to "see" the magnetic fields of the earth. While these may not be purely sensations related to the eye, I still believe the should fall under the category of seeing, especially considering that we don't have any comparable organs. My point is that we as humans were unable to determine the existence of things like electrical and magnetically fields until we constructed tools to heighten our perception so I wonder how much impute are we missing because our brain doesn't have the tools or the ability to process.
Yep, good science depends on questions/wondering. I'm not sure though that one wants to look for a reason why we are less "visually challenged" than other organisms, since other organisms, with quite different visual systems, coexist with us, and are, therefore, by evolutionary criteria, just as successful. Different, but not less good. Your second point seems to me quite solid. Indeed, our experiences clearly indicate that there have been aspects of "what is out there" that we haven't known about in the past and now do. So there could well be more such things. How could we find out about them? PG
The revelation is intriguing because I would have assumed that sight was part of the I-funcion. ("I see") To seperate sight from the self is very interesting. This new knowledge alienates me from my eyes and my brain. It is almost like they are part of some big scam and they determine what I think I see. Unfortunately this isn't a very comforting thought. No one wants to play the fool to their own nervous system.
I wrote in my essay last week about how the I- function is being limited more and more each week. This week I learned that the I-function doesn't control what I see. Vision is one of the most important and most depended upon method of sensory input. Perhaps, the I function is like some unwanted house guest in the nervous system and the brain doesn't give it many responsibilities, it just lets it pretend that it is vital to the working s of the nervous system. So what I will be looking for during the remainder of the semester is a reason for the I function. What is its real responsibility? Just to give us a sense of self? Does it have a concrete function?
Very nice, and much appreciated statement of the problem as I see it. Yes, lots CAN be done without an I-function. And that seems to me central to understanding behavior, as well as to trying to understand what the I-function DOES. And, of course, we'll talk more about this. I don't think its a scam, but it certainly seems to be true that the "I-function" is distinct from and doesn't know everything about lots of other things that are going on. Question, of course, is does it really want to? Are there advantages in being part of a community in which different members (boxes) do different jobs? PG
All of this brain extrapolation in the visual sphere discussion got me thinking about whether the brain infers in other contexts as well. But of course...people almost always go into situations with preconceived notions. The outlines which artists draw and the schemas and belief systems in people's minds can be used to examplify this concept. A group of lines, for example, may look like a stapler to people of one culture and a kind of rodent to people of another, due to these groups' differing points of reference. The ideas both parties bring to bear when making their interpretions of the image are a form of preconceived notions about the world. Similarly, the schemas or paradigms people bring to situations can act as filters. In other words, people might ignore input which does not fit into their preconceived contructs. Even if a person is aware of her schemas, it is difficult not to function in the world with a cognitive blindspot.
Another thing I was contemplating was how exactly I see the world when I'm driving down the road (For starters, everything outside is usually bopping up and down given my propensity for dancing while I'm driving). I was thinking in particular about what cues I would use if I only had one eye, and why far off places appear the way they do. If I only had one eye to work with I suppose I would estimate distance by the size of the object, with closer objects appearing as bigger. I would also judge distance based on color, with darker colors tending to recede and brighter colors tending to come forward. I'm sure I would need to utilize many, many more cues in order not to get myself killed.
Viewing things way far off in the distance is another story. People lose stereopsis (The angle becomes so small that both eyes see the same exact flat image) after a critical angle is reached. I suppose the distance to the critical angle would vary depending upon a person's visual acuity. In general, things tend to look grayer and bluer at farther distances because it is possible to see the effect of the colors being refracted by the atmosphere. Although, I have heard that it is harder to resolve the bluer colors than the redder colors because the higher frequency of the ultraviolet light causes these colors to scatter more quickly.
Three different, interesting, well-defined, maybe related? issues. Yes, lots of cues, so things may look a little different depending on which ones are available/used but lots of different ways to get more or less the same job done. And maybe the same for infering in general?, is good, not bad, that different people see things different ways? Maybe even good, not bad, that the "Rachel-function" isn't the only thing going on inside Rachel's nervous system? PG
One topic that I would like to briefly touch upon is the application of the blindspot. As the image moves across the retina through the blindspot on one eye, does it necessarily fall on the blindspot on the other eye? If not, when the brain takes the two images from the eyes and incorporates them into one, how does it take into account a non-input from one eye? Is there a hierarchal scheme for inputs?
Secondly, how is resolution created by the eye? Is there a limit as to the resolution? Several cell receptor widths? Is there a minimum number of photoreceptors that have to be activated in order to send a signal to the brain indicating that there is light present? And how does this relate to low light perception. One of the tricks that we were taught to do while patrolling at night was to slowly move your head back and forth. this had the apparent effect of amplifying ambient light quite a bit. Continuing with this, one of the noticable features of having strong visual acuity is fine motor control of the extremities, notably the fingers. We can see the minute differences in loctions of objects and feedback from nerves in our fingers can tell the brain where they are located. Did these connections evolve together or did one give rise to the other?
From skimming through the previous essays, I have noticed that hallucinations have appeared quite a bit. I too am curious about them ever since an experience a few years ago.. During a week long exercise, we were put into an state of extreme sleep deprivation and taxed both physically and mentally. As a whole, we did very well, but there were a few notable exceptions. One student ran down the Silver Strand Highway chasing after an imaginary cow. Later, during a 16 mile ocean exercise, one of my crewmates was convinced that a truck was about to hit us! My eyes were fine until the fog rolled in. After which, all I could perceive was patterns, notably plaid. Fortunately my ears worked, and I have never trusted my eyes fully since. What brings about these illusions?
Wow, a whole host of interesting/germane/significant observations/questions. Actually, you can check out the relation between the blindspots of the two eyes. No, they don't overlap. So yes, there is a resolving of ambiguity there too. Resolution is an interesting and complicated topic. To a first approximation, visual resolution is limited by the "grain of the retina", photoreceptor diameters together with subsequent connectivity. And the correspondence for the central fovea to receptor size is quite good. On top of this, though, there is a phenomenon of "hyper-resolution", an ability to detect discontinuities in patterns which are smaller than the sizes of individually resolvable spots. Want to try and imagine how that could be done (without magic?). And yes, we have much finer motor control than is obvious, as anyone who works under a microscope can attest to. How come? Interesting problem. Illusions? We'll come to more about those. PG
No answers, but its an interesting question (which is to say, one that might if pursued productively yield some good new observations/understandings). Some people seem more able to perceive 3-D in 2-D, and hence to more easily grasp how to make 2-D images that appear 3-D? Or maybe (my case?) 2-D images are so interesting in themselves that one doesn't feel any compelling need to make them appear 3-D? Other possibilities? How go about distinguishing? PG
So they I-function is not equipped to handle certain aspects of behavior and function. What is it equipped for? The I-function is useful because it can help the body to manipulate the world outside of the body and even use this world to influence the body itself. But the I-function does not always have the body's interest at heart. I can, if I choose, force myself to stop breathing. But biologically there will come a point where the I-function will be overruled and my body will begin breathing again regardless of my wishes ( my I-function that is). However, (this is going to get a little morbid so please forgive me in advance) I could choose to cut off breathing and the control of my body over breathing by using a rope or something similar. The point is that my I-function can choose to behave in ways that are detrimental to itself and to the body in general. A few weeks ago in class we talked about the problem of losing weight and how the I-function can be pitted against the body in that struggle. Losing ten pounds, however, is not generally all that detrimental to the body. But an I-function could choose to lose weight to such an extreme (anorexia for instance) that the body is at serious risk (and the I-function along with it). At the same time, the I-function can use its ability to manipulate the outside world in favor of the body. My I-function, and the I-functions of many other people make possible the wonderful advances in medicine, in food in clothing, in shelter from the elements etc. The I-function can give meaning and purpose to an individual, or a damaged self-image within the I-function can harm an individual.The exact extent of the advantages and disadvantages the I-function holds for an organism, and the relationship between the rest of the body and the I-function need to be explored in greater depth. I have tons more to say on this but I think I have written too much already.
Or alternatively, maybe we should just let you write and we can use that for the rest of the course? Actually, I don't think we're quite ready yet to take on the nature and usefulness of the I-function. There are still some more things to talk about that go on without it. But you're looking at the problem exactly the way we want to look at it ... anticipating large hunks of where (I think) we'll be getting to, and certainly approaching the problem in an eminently useful way. PG
There are times when this accomodating mechanism of the brain is not capable of reconciling disparate input. When this occurs the coordination of the body and the perception of the environment around the self becomes hampered or all together discombobulated. An example of such an occurrence is the visual-vestibular conflict that leads to motion sickness. If the inner ear can sense the accelerations and decellerations that occur when one rides in a car but the eyes focused on a book suggest that the body is in fact not moving then a conflict arises. The brain cannot adequately resolve this conflict and a feeling of illness results.
All of this is to suggest that our behavior can be based on perception of information that is not entirely correct; hallucinations have been mentioned in other posted discussions this week. It also suggests that the brain is not always capable of adequately reconciling these perceptions (accurate or otherwise) and so a distorted sense of the world results. This manifests itself in the most mild sense as illness or confusion. For example, one reason we sometimes feel disoriented or dizzy when we are very high up on a rock face somewhere in wyoming is because there are no close visual cues that help to establish a sense of perspective. Looking at the nearby rock face, or just sitting down, maintaining close contact with an identifiable sense (gravity and rock) helps to alleviate the feelings of confusion.
So, the brain isn't perfect and is trying its best to negotioate the dizzying array of sensory input that we receive every moment. good to know that it is working hard but scary to think that it is making a lot of educated guesses about my world!
Nice wrapping up of where we are with where we have been. Yes, sometimes the brain can't make sense of it all (remember though that the "brain" doesn't receive signals from the "nervous system"; the latter includes the former; its parts of the nervous system receiving inputs from other parts). The rock face is a nice example, and adds that the nervous system can itself influence its own inputs to try and make better sense of it all. Which, in turn, maybe means that the task isn't really to be "correct"? since there isn't any way to know what correct is? And hence less "unsettling" to recognize that the brain guesses (instead of knowing) and reguesses? PG
One test is to set up a bunch of colored squares around the blind spot and then observe how the mind actively chooses patterns and ratios of one color to the next. But if all the colors are different then the brain doesn't know what to do and makes it fuzzy and gray.
The brain is also capable of inferring complex patterns. If a recognizable pattern is set up with varying distances between spaced lines the brain is able to re-create the pattern in the blind-spot. Which leads to the interesting question of what if the pattern is recognizable to one person and not to another, is there a general limit to how complex the pattern can be or is it something that depends on the person? An interesting question that has the implications of being able to see more(your brain filling in your blind spot more accurately), the more intelligent you are?
It's interesting to think that we live our lives with these sizable spots in our vision that our brain fills in for us with out us ever knowing it. How many times have we seen something that wasn't really there or more importantly, not seen something that was there?
Probably not very many times because of the literal blindspot, since we actively move our eyes around all the time. On the other hand, as many of your colleagues have pointed out, metaphorically there are lots of blindspots and there is lots of filling-in going on. Glad you've been trying out blindspot things; there's actually lots of ongoing research in that area. It hadn't occurred to me to look at the issue of whether different people have different capabilities with regard to filling in "complexity", and I doubt it has occurred to others. Might be worth exploring. PG
Very interesting thoughts, that its all just "another form of creativity". We'll talk more about this, and dreaming. Is interesting that you see it as a positive thing, while some of your colleagues see it as negative. Wonder why? PG
In the model situation as we saw in class, the brain would be held fixed while the eye took in a single sight. Perhaps in this case the brain would be unable to react to abnormal circumstances that fall into the blindspot. However, this case is not true to life where the eyes are constantly moving, changing the input in and around the blindspot. In a real life situation, the blindspot would not be a hinderance to survival because it is only a small changing point in the larger scheme of images. We should trust our eyes not to betray us because, simply, they are too dynamic to be "stuck" seeing (or not) an important image.
Yep, eyes are moving all the time, so what we "see" is less restricted than it would otherwise be. Is good point, and worth generalizing for those expressing "fear and concern". Brain is largely trustworthy precisely because it doesn't base conclusions on one view but blends lots of them. PG
Nice story, very germane to where we are, and where we're going. Thanks. Do you remember what you thought after you hit the monkey? PG
Transduction in Vertebrate Photoreceptors
The purpose of this essay is to describe the transduction of ambient light into electrical activity within the rod and cone cells of the vertebrate eye. An attempt will be made to describe the relevant anatomy, and to outline the biochemistry of transduction. Phototransduction is the first step in transforming a pattern of light on the retinal surface into information which is processed by the brain, and which eventually is perceived by the organism as a visual image.
The rod and cone cells, so named because of their particular elongate shapes, are located within the retina, deep to the pigment and sensory epithelia, and superficial to the horizontal cells. Rods and cones are oriented so that the outer segment is superficial and the soma is deep. Photons that have passed through the translucent epithelial cells enter the outer segment. The transduced signal exits the photoreceptor via neurites which may synapse with other photoreceptors, horizontal cells, or bipolar cells. Although photoreceptors convey information, they neither depolarize nor generate an action potential. Instead, they hyperpolarize upon excitation by light, producing the graded release of neurotransmitters due to a series of biochemical events.
The outer segment of the photoreceptor is the site of transduction. In cones, the outer segment comprises invaginations of the plasma membrane to which the photopigments that mediate transduction are bound. In rods, the invaginations of the membrane detach to form a stack of photopigment-containing disks. The photopigment of rods is rhodopsin, a large transmembrane molecule composed of retinol and opsin. (The photopigments of cones function similarly to rhodopsin, but contain different forms of opsin, and will not be discussed in this essay.) When a photon interacts with retinol, which is embedded within the larger opsin, the retinol isomerizes causing rapid structural changes in opsin, which in turn cause further conformational changes in retinol. These changes bring about an instantaneous state of photoexcitation.
Photoexcitation of rhodopsin by a single photon engenders a chain of biochemical processes. Transducin, a G-protein on the surface of the membranous disk, activates an enzyme called phosphodiesterase (PDE). This enzyme reduces the cellular concentration of 3',5'-cyclic guanosine monophosphate (cGMP) by accelerating the breakdown of cGMP into 5'GMP. The presence of cGMP, the second messenger responsible for opening nucleotide-gated ion channelsl, allows cations, chiefly Na+, to flow into the outer segment. Reduction of cGMP concentration by PDE activity causes sodium ion channels to close, inhibiting Na+ influx. Meanwhile, the channels in the inner segment of the rod that allow K+ efflux remain open, thus the net positive charge within the cell decreases, and the membrane hyperpolarizes. An increase in the intensity of absorbed light lowers the cGMP concentration, decreasing the number of Na+ influx channels that remain open, and increasing hyperpolarization. The amount of neurotransmitter release is proportional to the amount of hyperpolarization, which varies not only according to the absolute intensity of absorbed light, but also according to change in light intensity. In the absence of light, the concentration of cGMP is sufficient to maintain equilibrium between the influx of Na+ and the efflux of K+via their respective protein channels, due largely to passive diffusion. Following photoexcitation, active transport via a sodium-potassium ion pump balances the ion concentration on either side of the membrane, restoring the resting potential.
Understanding the mechanism of transduction is essential to understanding how the eye adapts to different intensities of light, and how the deep retinal cells receive and process information. Also, transduction is important conceptually insomuch as it describes concretely how patterns of light on the surface of tissue become electrical signals in the nervous system, demystifying somewhat the process by which the brain "sees" what we see.
Demystifies indeed (at least if one is comfortable with cGMP, etc). And a useful addition for those wanting details (though I think you misplaced the photoreceptors relative to pigment and other epithelia). Thanks. And certainly documents the variety of voices with which you can speak.
One particularly interesting article posted on one of these web sites was an article about a young man who had been rejected from the military because he used ritalin. Apparently, the military will not accept any one who has taken Ritalin past the age of 12, since it is a "mind altering drug" and since it is evidence of academic problems.
i think that the angry response to Ritalin should serve as a reminder that many issues in Science, especially those in human neurobiology (since they involve the behavior and treatment of people) are social and political issues as well as scientific ones. Scientists have a responsibility to educate the public about new developments in research. Furthermore, makers and prescribers of drugs have a responsiblity to consider not just the effect that the drug will have on the brain, but also the efect that the drug will have on the person. I doubt that the doctor who prescribed the drug for the young man in the article, or the scientist who created the drug even considered that Ritalin could end his military carreer.
I VERY much agree that science relates to "social and political issues". Indeed, my own feeling is that it wouldn't be worth doing if it didn't. And I agree that there is hence an educational responsibility associated with science. Finally, I like your assertion that there is a responsibility for the "makers and prescribers of drugs", which isn't, of course, neccesarily the same community. Now, how do we get all those people to acknowledge, and seriously explore and exercise their responsibilities? Ritalin is a very interesting archetypal case of conflicting motivations and responsibilities. There are pages angry about it, and equally strong testimonials as to its value. We'll talk about some related issues a bit later in the course. PG
Likewise, one can consider that human bahavior in general often overlooks a blindspot that is the very nature of indivudality. A simple example would be one in which all people of a given sexual orientation are considered uniform...with little identifying features of indivudality. Here, the brain is receiving an input signal that is clearly distinct from the reality of the situation. Yet, human behavior generally chooses to integrate human excentricities into a uniform representation of a norm (popularized by the media,extremist groups etc). As was expressed in class, at least part of what an indivudal sees is not in the input signal at all. Can we say that human behavior, specifically in relation to brain function and control of emotions, is equally adept at covering up blindsopts in society, and instead focusing on a normalized, homogenized picture of reality? Food for thought...
And potentially very nourishing, if chewed on properly. Perhaps, though, the parallel is better to perception of color (which, in fairness, we talked about after you wrote this). Yellow, as we talked about, is a particular ratio of activity across a a neuronal population, irrespective of the wave-lengths of light which actually cause it. So the brain, rather naturally (and presumably usefully) tends to work in categories. The question is, how can one persuade the brain that the differences are at least as important as the category membership (and perhaps more so)? PG
Manners in which we learn involve all of our senses--sight, sound, taste, smell, and touch. If one touchs the surface of an object, one learns how it feels. If one smells a perfume, one learns its scent. If one tastes a particular food, one learns its taste. If one hears a song, one learns its tune. If one sees an object, what does one learn?
This is where I feel the issue of the blindspot comes in. We only learn with our eyes in what we can actually see. If one sees a tree, one perceives it as a tree. However, the marvel with the eye is that I can perceive that the tree is short and you may think it tall. We are so accustomed to believing what we see--not usually what we hear, taste, smell, or touch. But why seeing? It even goes back to the cliche, "Seeing is believing?" Everything seems so much more viable and truthful to oneself if it is seen with the eyes. This is because so much perception by the brain takes place. Now, I may be underestimating our other senses, but I really feel that the sense of sight gives us much perception in just about anything we do.
I'm a little confused about exactly how you see seeing in relation to other senses. You think of the blindspot as something good, something which represents the ability of different individuals to see things in different ways? Or as something bad? As in "we can only learn with our eyes what we can actually see", with that being limited by the blindspot and so forth? In either case, I think it is true that we as humans tend to rely more on vision than other senses (or at least we're more aware of that reliance), but I suspect that "blindspot" like things are equally as prominent in other senses. PG
I find it interesting that the brain can automatically make up for some of its problems (I wouldn't call the blind spot and the transfer from 2 dimensional images to 3 dimensional images a problem, but I couldn't think of the appropriate term), but not all of its problems. If people are color blind or have other types of visual and perceptual problems, then why can't the brain fill in the gaps there? My guess is that it has to do with damage to the color photoreceptors (if we are referring to being color blind). However, where the blind spot falls there are no photoreceptors and the brain makes up the information that is different from what the retina receives. So, technically even if the color photoreceptors are damaged, the brain might be able to make up something to accomadate for that damage. Perhaps the problem is that the connections from the retina to the brain that "fill in the blanks" are damaged. It may not even be the connections, it could be the messages that are different. If these messages are different, can the brain make sense out of them? When we learned that the brain receives conflicting reports about what is really out there, it can be understood that the brain does have capabilities to make sense of different messages. Well, my basic point is that why does the brain perceive what it wants to in some situations (makes up images to fill in the blanks), but not in others (i.e. visual problems)?
Interesting issue. Actually, the brain tends to do the best it can with whatever it has. That's why people are told to go get their eyes tested. Many problems aren't apparent (except perhaps in a general unhappiness) unless one tests for particular abilities and characteristics. Which is to say, the brain does a lot of filling in for various deficiencies, not only for the blindspot. (I hope for forum essays by the Tuesday after question posting, and usually clear the forum for the following week on Thursday or Friday). PG
I wonder if this is related to our tendancy to find visual order in systems, even if no order actually exists. We have the ability to pick out patterns, lines, and other organized components of an image with extraordinary ease. We learned that part of that is due to a tendency for our retinal ganglia to detect relative brightness and contrasts, rather than absolute brightnesses. The ability to quickly pick out the important parts of an image, without even thinking about (or really even processing) extra information is clearly adaptive. We don't see certain features of the world becuase we don't need to, processing that extra data would be time consuming and a waste of neural resources. If you are a primitive human, dodging angry bears, picking out the outline of a charging bear is much more important than absorbing all the information offered by the light falling on the retina.
Yes, avoiding bears is important. But I lost your argument somewhere on the way there. Or at least, what I thought was your argument. "our tendency to find visual order ... even if no order actually exists?" Yes, the lateral inhibition network provides some basis for this. What additional observations did you have in mind? Might it relate to the "categorization" phenomena/concerns talked about above? PG
I also wanted to offer a couple of websites for people who were interested in the "magic eye" stuff. The first is a paper about the use of stereopsis in advertising. It also gives hints on how to find the hidden images. The second has a few images to play with, and the third gives you the addresses of other websites which contain these images. Enjoy!
Interesting problem. At the moment, at least, most people working on dyslexia don't think that the seeing letters backwards problem is either a major contributor to reading difficulties or even a distinctive characteristic of dyslexics. But, its worth looking into more. Certainly, seeing some things backwards doesn't necessarily mean seeing other things backwards, which tends to suggest that different aspects of visual imagery are processed separately form one another (a theme we'll talk about next week). VERY nice sites. Many thanks. PG
This horrific situation, however, is not the state of world affairs. At least some people (most of them are not philosophers) believe in the concrete existence of their surroundings and fellow human beings. Therefore, instead of believing that the I-am-the-only-one-who-is-real philosophy is wrong, I believe it to be dangerous. I am of scientific mind, and so I generally enjoy the pursuit of truth, but not in this case. My logic neurons (and I use that term VERY loosely) take over and tell me spiraling towards depression is not how I want to live my life. Nor, for that matter, is it a productive way for anyone to live their life. So what if we are all imaginary? As long as I believe in the existence of my environment, other people in my made up world will, too. It keeps me happy.
I actually don't think one can go so quickly from "there is no way to prove the existence of anything" to "a big mass of gleaming egos and widespread anarchy". While there is in fact, insofar as we correctly understand the brain, no way to prove the existence of anything, there is equally, from thinking about the brain, lots of reason to believe in the existence of things. After all, the brain has internal models of something, which it continually checks by generating outputs and seeing if the inputs are as expected, and they frequently are. Since those models are similar in different people, its a good working assumption that there is actually something out there. And that, in turn, gives one some fairly strong reasons not only to believe in other people, but to care about them. They are helpful in evaluating one's own sense of reality. And its not only the similarities between people that are important but also the differences, since the latter help us each to revise our own models. So, in some ways, its better to be skeptical about any given description of reality (including one's own). It tends to make one more tolerant of others, instead of trying to destroy them because they see things differently. "Unresolvable discussion" or interesting issue?
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