In the eighth grade I read a bad fantasy novel about the fight between the good and evil forces being fought by strong and valiant warriors against decrepit and tortourous sorcerors. What, you ask, does this have to do with percieved reality or the eyes? Well, when the good guys were fighting the black magic, they had to enter some sort of meditative state which, after they left it, caused them to be able to see and feel more of the natural world, and broadened thier perception of reality. When we discussed the visual feild and how it shows jsut one area of reality, whereas we are not equipped to sense all things in nature, it reminded me of these daring warriors.
The analogy is even deeper. Scary. The increased ability of the good guys to perceive other realms of reality did not help them, but caused them to have trouble fighting. They were unable to focus on their actions and were left impaired until the strange ability lessened. If we were able to have the ability to see like hawks, smell like dogs, sense electromagnetic poles like horses, hear like owls, or have any other seemingly advantageous increased sense of reality, we wouldn't be able to focus very well. Our ability to concentratate our senses to produce our personal reality would be strained, and the world would appear to be a cacophony of sensory input. By having limited sensory capabilities, we are able to make a somewhat concrete picture of what we do sense. The limited world that we perceive may be different than that of all others, but it is nonetheless much more real, in that it can be understood, than if we were able to sense all aspects of reality.
Very interesting, in both directions. Yes, is probably true that our nervous systems would be overwhelmed by too much information. At the same time, it is nice to have the capability to appreciate the existence of alternate realities ... and to make use of them ourselves at times. One might make an argument that that is what science is all about. PG
We spend our live forming new neural connections, making new chains of RNA molecules that constitute the chemical basis of our memories, and creating a framework of belief. Reality is perceived by each human being in a different way. Its perception is shaped by previous experiences, emotions, and cognitive facilities. According to the dictionary, objectivity has many meanings: being free from personal feelings or prejudiced, being unbiased, being intent upon things external from the mind and of or pertaining to what is known and composed of or relating to things that occupy space and can be perceived by the senses. But the dictionary fails to take into account that the senses themselves are already biased in some way.
Knowing that our world is not fixed, nor our Truths known, objectivity is outside the realms of humanity, since we are shaped by the way that we interact with the world. According to Einstein the only measurements which are ever truly objective are those made by machines, since they are calibrated to take only a particular reading. When we take these readings into the nervous system, there is already a degree of subjectivity. The sensory interface has a predetermined range of experiences that have developed over eons to best accommodate our environment. The eye is attuned to perceive edges, to decipher a world of contrasts, the nose and taste receptors have a very particular range which is narrower than many other mammals, and our range of touch is not quite as broad nor sensitive as other creatures. Thus since we are constrained by the boundaries of our body we cannot know nor sense everything in reality. Our knowledge being incomplete - objectivity remains some unattainable ideal.
We live in a circular loop, whereby we act upon reality and it in turn changes us. The model that we have of reality is one that we agree upon within ourselves. We can share our personal interpretations, the output of each individual mind, but it will always remain individual and subjective. The search for the closest approximation of objective reality is an integral part of striving to further clarify and draw away from ignorance the principles whereby we govern our lives
Relativism is the idea that the world, our reality, is in constant flux.> This principle applies directly to the way the nervous system interacts with the world. Our perception of the world is constantly changing. We have within us billions of different neural pathways and the probability of any particular path being chosen is completely indeterminate. The particular combination of excitatory and inhibitory stimuli that will arrive at any particular moment will determine which pathway is taken. It is the way that the nervous system conveys the information to the cortices in the brain that is the first step in translating an objective world into the subjective world within us.
Thus we see a world built of the nervous system's imagination. Because of the way we sense the world, there are particular concepts or ideas that we can guess at, and feel their secondary effects, but never truly experience - eg: our present model of the atom. We believe that it is circumnavigated constantly by an electron because such a model best fits the interpretation of the results we have found. But, we have never truly been able to measure the position, nor the speed of this particle at the same time. An uncertainty principle, which is the foundation of how we perceive reality. Since we have a narrow range, and in some places blind spots, we can never truly be sure of what is actually our there, or what we are filling in.
LOTS of interesting thoughts (be careful, though, about RNA as the repository of memories; it ain't (of course) that simple). Yes, we affect things outside of us, which in turn affect us. And yes, our inputs are limited (at any given time). Most interestingly, it all does raise an interesting question about the meaning of "objective", a term which is of course also a product of the brain, and hence subject to change. Maybe it isn't the "world" which is "objective" (a poor definition, since we can't, as you point out, ever completely see that), but rather a process of the brain which constitutes "objectivity"? How about the possibility that "objective" means what is similar in the potentially very different understandings of "reality" that different people have? Or, maybe even better, "objective" is the process of trying to specify and make use of those experiences which are common to everybody (or at least lots of people)? PG
The thought that our eyes do not receive all information present in the outside world and process it exactly as it is is not a promising sign that we have a clear perception of reality. I'am pretty sure everyone's sense of reality is different or we wouldn't be arguing over it. But how different is it and is it gender or age related? And why does light excite and inhibit? What is the purpose of inhibiting?
Our eyes are not the only organs we use to obtain a picture of reality. We also use are nose, hands, mouth, etc. to obtain a more complete picture or reality. Many of us know from experience that the eyes often deceive us(magic tricks, mirrors, illusions) and can not be relied on to obtain information about reality. Once, I read about a woman, with some kind neurological problem or damage to her brain that mistook her husband for a hat. From what we have learned,that doesn't seem impossible.
Not impossible at all. And you've mentioned an additional important idea: that we constantly check what we think we see through one input pathway against the information along other input pathways. And we also check our own pictures against those of other people, so maybe, with all that checking, there is less difference in peoples' sense of reality than one might at first think? The purpose of "inhibiting"? It helps to maintain object constancy, i.e. to be sure that the signals in the brain resulting from something outside are pretty much the same even if the circumstances change. Understand how that can be from the lateral inhibition network example? PG
We, human beings, consider the norm to be "reality". However with the knowledge that the brain makes up alot of what we think we see, the concept of reality changes. It opens doors to questions about "reality" and just how reality differs from person to person. This I can accept, the part of how the eye works that confuses me is that the signals fromteh ganglion cells are more or less the same signal except for the edge of where white and dark meets. So, our perception of an object before us are different light intensities affecting our retina. If this is so, than at night, when our eyes are closed, where are the pictures we see in our dreams coming from? We "see" in our dreams. This is not part of an I-function, most often in dreams we are not "aware" of our dreaming. Where are the different intensities coming from that form the images in our dreams? And if what we see is our reality would that not mean that our dreams are reality as well. The functioning of the eye and lateral inhibition are all very useful and I understand how they affect our input-sensory side however there is alot of unanswered phenomenon.
Yes, indeed, some interesting questions about what is meant by "reality". And yes, what the retina tells the rest of the nervous system is mostly (though not entirely) about the edges, with the rest being filled in by other neurons. Which is to say, being "made up". Does that help in thinking about dreams. I think so (though we'll talk more about them in the course in a bit). Basically, it says that things "made up" are actually not so surprising. So dreams are not so surprising, and are (presumably) simply patterns of action potentials like "seeing" is. And I'll argue with you a bit about whether they aren't perhaps a function of the "I-function". One certainly isn't conscious in the sense of responding to the outside world when one is dreaming, but one is, in some sense, THERE. PG
> We did a test with a peice of paper to see our blind spot, and directly observe how our brain makes up information. While this little spot may not seem like that big of a deal, it shows how our sense of reality can be distorted by our brain. This small distortion can lead to serios concequences. In the evolutionary scheme of life, a small blind spot would not that detremental. But in our complex life, where so much input is being taken in, and all of it is important, a warped sense of reality can be bad. A specific eaxmple of this is the rear view mirror in a car. if you are focused on the road, the road is like the x we drew on our paper. And depending on how yu are sitting, the rear view mirror can be in the exact place of your blind spot. People have had many car acidents because they do not see a car in the rear view mirror.
Also, this makes us wonder whether there are other things which are present in our world which we are not aware of. Obviously, we have no sensors for them, so we would not even know that we re missing them. We know that there are many levels of sound which we cannot hear, and we don't have night vision like cats and other animals. So perhaps there is a limit to the amount of sensory input one brain can hadle. We have a large range of input, but perhaps if we had the hearing range of dogs, and night vision like cats, and magnetic sense like birds there would be too much information to correlate.
Interesting thought, that our sensory limitations (and those of other animals) are because otherwise "there would be too much information to correlate". On the other hand, we (at least) are constantly striving to increase our sensory abilities (glasses, telescopes, microscopes ....). Does that give us too much information to correlate? Maybe. Yes, blind spot only a small example of wide array of ways the nervous system "makes things up" (actually the CAR blindspot is a different thing, having to do with how the car is built and what it blocks from view). And, in general, it may be not so much "warping" and "distorting" as improving on the information we have available (as in the checkerboard constancy despite varying illumination). PG
Studying the sensory nervous system reveals a great deal about our sense of reality. Our respective experinces of the environment differ dramatically depending on, for example, how much light may be passing through the window we may be sitting under, as compared to someone else sitting in the relatively dark corner of the room. The image of our environment that is superimposed on to our retinas becomes one of our most informative methods of gathering pertinent information from the environment.
Someone who has poor eyesight may not experience the elation that I feel when the sky is perfectly clear and I can see that the flowers are beginning to bloom. This part of my reality may simply not exist because to this individual because they cannot percieve the signs of spring due to impaired sensory apparatus. >From what we have learned about the visual system in particular, I feel that reality is completely subjective, due to the extraordinary number of differences that we experience due to our interaction with the environments.
There's certainly a subjective element in any given person's idea of "reality", for the reasons you give (among others). And that's important. So too are some things we have yet to come to. A continual testing of one's idea of reality against additional input. By that device, one's "reality" can change, and perhaps become more "objective"? PG
The nervous system is sensitive to changesit is designed to detect edges and differences between light and dark areas in objects, disregarding changes in light intensity. This suggests the viewpoint that change is more important than the periods of similar conditions between them.
What we see depends greatly on what exists around the object we are looking at. It is the comparative difference in light intensities between surfaces, rather than the absolute light intensity on each separately, that is of prime interest to the nervous system. While we dont seem to notice things while they stay constant, change gets our attention. This supports the idea that, in general, it is the changes we notice and not the stable conditions that exist between these periods of change. For example, when we cut our hair we can feel the change in its weight, even if the difference in hair length is very small. Could this be the work of those corollary discharge signals reporting to a center in our brain that our hair is still 3 feet long, only to meet with contradictory sensory input signals reporting our hair is actually three inches shorter? Over time we become used to these changes, and our hair doesnt feel so noticeably short anymore.
These general principles of sight and of sensory perception can be applied to our larger sphere of behavior. We dont notice the shoes we are wearing until they start to hurt. We dont notice our the weight of our hair until we get a haircut. And in a broader sense, we dont notice the importance of a relationship until it is altered, or gone. We dont notice how cold and dark Winter was until Spring comes with warm breezes and long, bright days (were still waiting). We dont seem to notice things until they are altered or missing. This view of the nervous system, therefore, gives us insight into our own behavior on a larger and more complex scale.
Interesting and appropriate extension. I'm not sure I'd call it corollary discharge, but we certainly have internal models of reality (to which CD's contribute) and tend to pay attention to sensory input more when it is inconsistent with those models (something has "changed") than when it is consistent with them. PG
First some questions. Why does the retina only have one "fovea"? Why might such a region have evolved? What's the purpose of amacrine cells? Why is a ganglion cell not a good photocell just because it has a large recpetive field?
So, the structure of the eye and retinal processing demonstrate how and why what we see is largely determined by the "filling-in" of the brain. We can do little experiments to show that the brain does fill in and we know that it fills in because of the blindspot created by the optic nerve. We know the what and the why but not the how. To a certain extent, we know that lateral inhibition is the how...it enables us to see changes in light intensity. Given this, it would make sense that we fill in with the surroundings because at the blindspot there are no photoreceptors that would allow us to detect such a change. So by deductive reasoning, if there is no change then it is the same. But why don't we just see black at every blind spot since there is no light received by the retina in this spot? Is it that the blindspot is so small in proportion to the object in vision? Is it that our brain fills in the spot after processing the state of the surroundings? Or is it more of a stretching or a bridging of the surroundings that is more the responsibility of our eye than our brain? That our brain can fill in aspects of visual stimuli suggests that it does the same for other stimuli. We know this occurs in language in which you may not "hear" every syllable of a sentence but you can fill in the missing ones using the ones you did hear. You may even report having heard every syllable and can play back the way it sounded in your head. What I don't understand is why such effects don't always occur. Is it dependent upon the quality of surrounding info you get or on previous exposure to the syllable that you missed? Probably both. Concentration obviously is also a factor.
Lots of questions (as appropriate). Isn't the large field that makes a ganglion cell not so good as a photocell but rather the fact that some areas of the field excite it, others inhibit it. Some animals have more than one "fovea" (or at least more than one area with sharper vision), others don't have much of one at all. So "foveas", like many other things in biology, work for those animals that have them (presumably making it possible to see some things more clearly). Amacrine cells mediate lateral inhibition between the middle nuclear layer and the ganglion cells and tend to be involved in motion sensitivity (which we haven't talked about but is described in at least one of the Scientific American articles).
Filling in? Yes, happens all the time. Even more than you might think. Which suggests that the "picture in the head" is actually there prior to any inputs. Then things aren't so much filled in as left undisturbed. Its actually an active area of research, so if you're particularly interested I'd be happy to give you some places where you could read about it. PG
Perception is an extremely subjective interpretation of inputs that may or may not involve the I- function as a contributor to the subjectivity, but it depends on the kinds of inputs that the nervous system can receive, i.e. on the kinds of sensory receptors that the nervous system has incorporated into its repertoire. Thus our interpretations of reality are ultimately based on the kinds of information that our sensory transducers can introduce into our nervous systems. The kinds of receptors that organisms possess, and their level of functioning usually remains fairly constant within species, but some variations may be seen. Thus amongst humans, most people can see all three primary colours of light, and myriad of colours formed by combination, but some cannot, and are hence "colour- blind". Colour- blind people's view of reality hence must be vastly different from that of "normal" people.
As far as depth perception goes, it is based on the accommodation abilities of the lens and its adjunct ciliary muscles and suspensory ligaments, and the ability of the brain to monitor the intensity of the image on the retina of BOTH eyes. If one eye is closed, or not involved in the depth perception process in some way, it becomes much harder to estimate distances. Thus both eyes are obviously necessary for the correct functioning and interrelations of the brain and retinal signals. But this observation then raises the question as to how much more input does the brain have into the final picture of the object that we carry in our heads, distinct from the image of the object on the retina?
Using the above observations coupled with those from blind- spot tests, it can be seen that the brain provides a significant portion of the picture of "reality", implying that nothing, then, in terms of how we see the world, is absolute. There can be no standard against which to compare differences, at least in terms of those components of the entire picture that do not use input from other sensory transducers. Thus shape may be considered to be reasonably accurately detected by the tactile senses, as can be texture and temperature. But there does not seem to be any way to absolutely compare components such as colour, which depend purely on the visual senses, leading to highly subjective descriptions of colour.
Everything is "subjective", for the reasons you give. At the same time, also for the reasons you give, it can become more and more "objective", by checking the "reality" using other senses, as well as by trying to understand how the same things are felt/seen/understood by other people. In the last analysis, though, you are right, that we like an absolute standard by which to evaluate the veracity of our pictures. That ok? PG
The general principle garnered from analysis of sensory input to the nervous system is that the system actually constructs human reality. It is apparent, through many different characteristics of the nervous system, that sensory input is subject to a great deal of interpretation and maniputaltion to produce what is ultimately experienced as reality. A primary example which illustrates the capability of the nervous system to construct reality is the lateral inhibition network of the eye. Upon exploration of this system of neurons, one finds that the brain is actually infering information about reality and placing it in our reality. The nervous system does not receive the sensory input that corresponds directly to the output that is reality.
There are a plethora of other examples which indicate that the nervous system is making up information, many of which neurobiologists are probably not aware. The implications of the fact that the brain constructs much of human reality are wide-reaching and powerful. They essentially indicate that the reality that exists as the universe is much more complex then the human can percieve. However, through the selection of evolution, humanity has only retained the necessary sensory characteristics to allow the species to survive as best as possible. The physiology of the human body has evolved so that in a universe which contains many different types of potential sensory information, humanity must only make use of some to sort out the complexities of true reality. For example, if we were able to detect all possible waves of the electromagnetic spectrum, it would be impossible for us to distinguish what should exist as reality. However, there are other species which have the ability to detect other wavelengths, defining reality for them.
In terms of behavior, the concept that the brain actually processes sensory information through interpretation and manipulation and outputs a reality dinstinctly different from that which is inputed may help in explaining some of the aspects of behavior that have been deemed difficult to explain. Should neurobiologists have the ability to determine the workings of the brain in terms of how it presents inputs as outputs, there will not only be a better understanding of the universe as a whole and the nervous system, but also the uniqueness that is human behavior.
A pretty ambitious task for neurobiology, but I actually agree with you in principle. Clearly though different organisms have different "realities", as you say, so one can't exactly say that humans have those that are "necessary", at least not uniquely necessary. Can you be more specific about why we have the limited set of inputs we have? And perhaps about how this all explains "some of the aspects of behavior that have been deemed difficult to explain"? PG PG
What effect does studying vision have of the perception of reality? I remember you saying in class a while back that the creation of the picture that each of us has of reality is not a passive process, but is an active one. That struck me. Everything that we encounter and that we see (well maybe not everything) is processed and incorporated into our reality. I don't think that the brain filling in the blind spot on the retina makes a large difference is the our senses of reality, but I think that it makes an interesting example of how the brain can "fill in" information that isn't really there. Based on past experiences or mood, etc, the brain can take an ambiguous situation and fill in the information and details it and make that reality. This is what a lot of psychological tests bank on (the TAT for example studies people's personalities by looking at how they interpret ambiguous pictures.)
What is reality anyway? It seems that reality is the way that we perceive the things in our environment, and part of that has to do with our experiences and the pathways we have built in our brains for processing, and part of it with human biology. There are many things in our environment,(sonar, infared, radio waves,) that we are just not able to consciously perceive, while other species may be able to. So reality is specific to a species. I would guess that this is somehow advantageous, and that each species develops a way to perceive sensory input that it needs. But not only is it species specific, but reality is different for individuals. Granted, as a race, humans in a given culture have generally the same sense of reality, but differ on thousands, millions, of points. Look at the way that someone who disagrees with Newt Gingrich will portray his image and what he stands for, or the way that witnesses to the same crime will report a different story. What they are saying is real for each of them, but it is different because of the way that they perceived the talk or the situation. So in a way, it seems like what you actually see is a pretty small part of what it means to have a sense of reality. The brain has a lot of influence on how that input is processed and recorded. Hallucinations are another example. When people see things that aren't really there. Hearing voices is another example of a neurological abnormality interferring with reality, but we're talking about vision right now. When someone sees their house on fire or suddenly finds themselves reliving a scene that they saw during a war, their brain is creating these images and making them seem real to the person. It's scary.
Good points, but also worth dissecting them a bit more. Yes, of course, the blindspot is one example of a much larger array of phenomena of organisms and people "seeing things differently", and its important to understand that they do. It also helps to keep in mind that the differences can occur at different levels of organization, and have different explanations. The blindspot is a very "peripheral" (close to the edge of the nervous system") effect, and probably largely genetic. How one sees Gingrich is a much more central effect, and much more a function of experiences/education. Some differences are more fixed, others more labile, and so forth. And, as we'll see in a bit, "consciousness" adds an additional layer of complexity. One doesn't have to be "conscious" of seeing things to see them in a particular way, different from how other organisms/people see them. Scarey? Yes, in one sense. But exhilirating in another. No organism (or person) can see everything. But if everyone sees a little bit differently, and we share what we individually see, then ....? Maybe there's a good reason for science, and talking about things, and so forth? Maybe "reality" is what we collectively work out, together, from all our experiences? Would that be so bad? PG
Compared to some other organsims such as insects, our sensory side of the nervous system seems to be different in many ways. We have restricted sensory transducers for sight, smell, electric, and magnetic fields. Birds can detect magnetic fields much better than we do, enabling them to fly north or south depending on the weather. Different organisms have a difference in the function of transducers. It seems to be because organisms live in different environments and evolved to have just a number of necessary transducers for survival.
Insects have more precise transducers for vision. Some insects have numerous numbers of eyes and are able to see things more precisely. Others also have unique transducers to see patterns on plants from ultraviolet rays. It is a question why we do not have the same ability. Maybe it is because we do not need such precise vision to survive. Our brain is able to allow us to view the three dimensional images from the rough information that is processed through the eye. The operation of the lateral inhibition network allows us to see a form of reality more realistic than the information which is provided. It allows us to see constant colors for permanent objects (checkerboard) although the amount of light intensity may change.
It is interesting to know that the brain is able to cover up and make an image for the hole we have in our eyes. It tells me that the brain has uniquie abilities to try and create a sense of reality for us. What we may see as reality may not be as realistic as it actually may be but the brain seems to be doing a good job in helping us think we 'see' reality.
In fact, unless we learn about what other organisms do, it rarely occurs to us to question that "good job" the brain is doing. In that sense, other organisms help us to appreciate a broader reality than the one we normally see. Presumably that one is good enough for us to survive, but its nice to try and expand it, no? PG
i understand the mechanics that we have been discussing about the photorecpetors and eye function, but i still haven't fit together exactly HOW we see. it is confusing to think that what we see everyday is simply light intensities that our photoreceptors detect. i have trouble attributing the shape of a circle to various light intensities. images on our retinas are just results of permeability changes on the photoreceptors from the light intensity outside. even though i know that this happens because i particpated in the experiment in class, i find it difficult to accept that our nervous system fills in the points where there are no photoreceptors on our retina. in other words, because we aren't AWARE of this happening, our sense of reality isn't really reality!! also, the idea of lateral inhibiton is logical, but, at the same time, it provides evidence that what we see is not always what is true. for example, our eyes fill in lines in black and white spaces when lines don't really exist. it is difficult to know when this occurs if we aren't aware of it--it happens and we think we're seeing something that isn't really there. the whole lateral inhibiton idea leaves alot for the eye to choose as what it belives is reality. in calss we said that inhibition and excitation will cancel each other out--therefore, this is not necessarily an accurate representation of intensity. this certainly leads me to wonder when we see what we see, what are we REALLY looking at versus what our eye reports to us. no two eyes will ever receive the EXACT light intensities, nor will they have identical photoreceptors and retinas so now two people can accurately compare their own realities--this gets awfully confusing. at any rate, i am anxious to piece together just how these intensities on our photoreceptors and retina get transformed into images, colors, and textures. also, i thought that the "image" on the retina is upside down--when does that get fli-flopped? although the question of "reality" will never be answered fully, we can probe the issue of seeing more deeply (and i know we are) so as to undersatnd the mechanics of the eye and the job it carries out for us to see what we see everyday. i was also hoping we oculd discuss the problems assocaited with various blindnesses.....maybe that can be something for in-class discussion.
We'll get to at least some blindnesses. In the meanwhile, its worth noticing one you seem to be shedding. Yes, what the nervous system is doing is a little disorienting when one first encounters it. And yes, it raises some interesting questions about "reality". It also, as you say, helps to better understand "reality" (which, of course, it itself is), and encourages one to be continually curious, since you never know. That ok? PG
Our interpretation of reality is greatly in the hands of our nervous system. Since we are able to experience only that what our nervous system allows us to experience, the question of what reality actually is, is difficult to answer. The only reality that we know is that which results after being processed by the nervous system. Even if there is a greater reality beyond that what is detected by our nervous system, we are unable to experience it because of the limitations of our nervous system. In terms of vision and sight, what is to say that what we see is what is actually out there. A great example of how powerful the nervous system actually is in influencing our experiences is the phenomenon of hallucinations. It is not an uncommon phenomenon for people to hallucinate and "see" or not see things that the rest of us are unable/able to see. Furthermore, when in a hallucinatory state, it is possible not only to see things that are not seen by others, but also to smell, taste, and touch these things. According to the person having the hallucination, he/she is definitely experiencing the object(s) in question, and so the object(s) is a a part of his/her reality. However, according to the general public, the object(s) is not a part of reality. This raises another question-do we really have the right to judge/determine that what constitutes another person's reality, and deem it real or unreal by comparing it with the general experience?
Nice point, nice question. Maybe we should simply accept that there are personal "realities" and public "realities", without calling one "real", and the other (perjoratively) "not real"? Could that be done? What problems would it raise for individuals/societies? Are they soluble? Would things be better in some sense if one went that direction (which is indeed what understanding the brain suggests is the "right" direction)? PG
What does studying the sensory side of the nervous system say about your sense of reality?
I guess at face value, it would indicate that everyone's sense of reality, theoretically (how do you spell that word?), could be different. Or maybe even should be different. As far as I can tell, everyone may very well have the same sense of reality, but how would you know.
There is an old theory on pain. Is it possible for someone else to "feel my pain?" Even if all of the same sensory neurons were fired upon impact with a baseball bat--I'm fascinated with baseball--how do you quantify pain? The answer is, you can't. That is why everyone's reality is different. However, everyone who gets hit with a baseball bat feels something. Quantitatively, that "something" can be compared to other impacts felt in the past. So, everyone's sense of reality is not all that different.
Perhaps it is degrees of pain, or pleasure, or sadness, or bliss that makes an individual indeed an individual. But, since we are all, for the most part, given the same tools (sensory neurons, ionic concentrations, etc.), we are only individuals in the by the strictest definitions. I think that everyone's sense of reality is the same--we all feel pain when the bat hits us. But, rather the difference is in the interpretation of that reality. There are masochists who love pain. And there are people who whine when the dog runs into his leg (not that great of an example, but you know what I mean). It is these perceptions and conscious interpretations of reality that defines the individual.
Interesting explorations. I'm not sure there is as sharp a distinction between "feeling" and "interpretation" as you seem to suggest there is. Both are action patterns of action potentials in neurons and (despite your thinking we have the same tools) there is a lot of individual variation in those both close to sensory cells and deeper into the nervous system (where they correspond to "interpretations"?). Regardless, I agree that what we've talked about implies that "everyone's sense of reality ... could be different. Or maybe even should be different". Want, maybe, to explain sometime what you were thinking when you added the "maybe even should be different"? I think that's important. PG
I have always been amazed by the intricacy and delicacy of the sensory systems, especially that of vision. It seems a small miracle that people have senses at all; because when the slightest problem occurs, the whole phenomena is wiped out or terribly impaired. Yet, when we consider the instruments that science has concocted to detect various electromagnetic wavelengths, sound waves, and so on---humans have very limited capabilities to sense in the larger scheme of things!
Perception is amazing in this way because of how people develop their sense individually and how dependent some people need to be on devises or other human beings because they have deficient sensing. Many people (myself included) are near-sighted and need to use additional lens to be able to see "normally", but blind people do not have this option at all. These people need to use their other senses to adapt in order to be able to function. It is often believed that people with sensory impairments must "develop" their other senses to some super-capacity but I have not heard much proof of this. Rather, I believe that they just pay more attention to what information their other senses provide and are therefore just able to use them more efficiently and not waste information provided to them.
Sensing is a leap of faith. It is believing what you are seeing, hearing, feeling etc when you never ever really know "for sure". Most people do not question their ability to sense and never doubt what their senses are telling them because there is no where to turn to for answers . There is a great deal of room for doubt in what we sense but no way for us to close off this gap--it is either leap or stay still for the rest of your life. This gap lets us make perception mistakes but considering how "right" we "feel" most of the time I would say that it is a good bet. Still, judging the security of our bet is difficult being that our sense of everything could be terribly scewed or inaccurate. I prefer not to second guess myself and just accept the fact that I will never know what I am missing and pretty much prefer to stay that way.
You've put your finger on a central issue that does indeed fall out of thinking seriously about sensory systems. Yes, it means there is always "room for doubt". And yes, of course, it means "seeing" depends on faith, and usually it turns out to be well-justified. But that doesn't mean one has to "stay that way". As you point out, humans have the capacity to extend their senses in a variety of technological ways. They have as well the capacity to "see more clearly" by sharing what they see with others. So, maybe without "second guessing" one can use the knowledge of limitations to get better? PG
I have always been fascinated with the experiment that we did in class showing that the brain fills-in information into the area where the blindspot is located. The brain is involved with what we perceive to a much larger extent than I realized. An important question is, how much can we rely on what we perceive?
I was not sure what you meant when you discussed that idea that the brain gives us a clearer picture of what is out there than what reaches the retina, but I suppose we'll talk about it more in class. Debbie :)
Has to be relied on, to some extent, since its all we have. On the other hand, it should always be treated skeptically. Which is to say, one ought always to check what one perceives by (as one normally does) seeing whether a different way of experiencing it yields a similar result and by (as one also normally does) finding out whether other peoples' experiences yield similar perceptions. Yeah, I'll go back to the idea that what we see is clearer than the information we get about it (at least a couple of times. PG
Professor Grobstein, to some degree you have answered your own question about what studying the sensory side of the nervous system has to say about our perception of reality. We now recognize that it is limited in many ways, from our brains "making things up" when they are not sure about visual details to our ability to "see" with only a fraction of the sensory mechanisms available. But, while it would be nice to detect ultraviolet light, magnetic fields, or electrical signals, we have to acknowledge that our sensory systems can only be described relative to those of other animals, and not to the absolute standard of perfectly reflected reality, which is probably impossible. What I mean to say is that the input side of our sensory system is thousands of times too complicated for our needs anyway. Evolutionarily, our senses, combined with our dexterity and complex brain have allowed us to run away with control of the world in many ways. We don't need to sense any more than we do to survive.
Our lateral inhibition network is good for making our eyes quite sensitive to intensity, and combined with the sharp edges our nervous system values so much, we can see shapes and shades and therefore view the world in three dimensions. Also we have the huge advantages of seeing in color and being able to focus closely with the fovea area. By contrast, a frog, as I have been told, sees well a foot or so around him, and needs movement to distinguish shape. This tells me that he has a poor lateral inhibition network that is low in sensitivity. On the other hand, though, he sees in the round, and most certainly he has supplementary sensory mechanisms that we don't.
Maybe we see centers the same as edges, lack night vision, and are confused by some patterns. But we see reality just fine for our survival and nature keeps us from absolute power over all other organisms by denying us their sensory advantages. Similar to the confusing artificial patterns we saw in class are the patterns of camouflage our prey and natural predators (when they were actually our predators) use. The ability of a mosquito to sense our heat while we cannot see it coming in the dark until it is too late keeps it alive. The fact that sensory systems are at least somewhat balanced is an advantage to the reality we do not fully perceive because it creates a diverse world that we are competitive in and a part of, but not quite masters of.
Fair enough, as long as we accept (inherent in what you say) that "seeing reality just fine ... for survival" is equally true of ALL living organisms and not exclusive to humans. "Run away with control of the world"? There's certainly a concern there, but I suspect there's also a bit of hubris: I doubt mosquitos (and many other organisms) are much concerned (and may not in fact be much threatened; the most obvious threat we pose is to ourselves). It would (perhaps) be nice to imagine that nature was smart enough to make us participants but not masters (by giving us and other organisms offsetting sensory advantages), but I suspect nature has pretty much just been playing around and so its up to us to learn what we can from the different visions of different organisms (and different people), and to try and derive wisdom from it. PG
The fact that the information the NS receives about the outside world isn't exactly what we _know_ about the outside world is quite a surprise to me. It shows that there is more to "knowing" reality than having a functioning set of sensory mechanisms; there is something going on internally. The concept of our brain "making stuff up" is what especially baffles me. If there are so many things being fabricated by so many different brains, how is it that we are able to have such similar perceptions of reality? Perhaps relativity plays a key role here in that our perceptions seem similar only because our brains compare things similarly.
The brain's "creating function" may also be a biological basis for the discrepancy between individuals' observations, which might lead to sociological applications.
Pleased to be surprising you (is what education is about, no?). Yes, interesting social implications (a good argument for appreciation of diversity). Which is, also, some explanation for "similar perceptions of reality". Some of this, of course, has to do with similarities of different brains. But a lot of it is even more interesting, and results from exchanging ideas/pictures among people with different ones to see what might account for all the varied things seen (you know the story of the wise men and the elephant? none see the elephant very well but collectively they do a pretty good job). PG
In cognitive psychology visual perception is conceptualized as a progression from (a) a "raw primal sketch"-- a sort of intesnity map, an initial representation from the senses; to (b) a "full primal sketch", or an intensity map that includes markings for edges, regions of similar intensity, and contours; to (c) a "2-1/2 D sketch", a representation that includes depths and orientations of surfaces relative to the viewer. It is assumed that objects within the visual field are then somehow compared to 3D models-- one for every object in the world-- that are stored in long-term memory so that object recognition may take place. What was discussed in lecture this week relates directly to the concepts of the raw primal sketch and the full primal sketch.
The raw primal sketch, being a simple intensity map, may be equated quite simply to the output of the photoreceptors-- permeability changes that "fairly faithfully copy the pattern of light on the retina." More interesting is the derivation of edges and contours-- the full primal sketch-- from this intensity map, which is the work of the ganglion cells. The shape of the receptive field of these cells, otherwise known as "center-surround cells", is critical to understanding this derivation. The ganglion cell's receptive field, called a "concentric center/surround antagonistic receptive field", is shaped somewhat like a bulls-eye. Energy striking the outer region of this receptive field (in the case of a "center-off, surround-on" cell) results in increased activity in the cell, whereas energy striking the inner region of the receptive field results in decreased activity in the cell. (Alternatively, in a "center-on, surround-off" cell, these excitatory and inhibitory areas are reversed). A cross-section of the excitatory and inhibitory tendencies one of these (center-off, surround-on) cells might therefore look like this:
+1 -2 +1Where +1 indicates an increased firing rate in response to energy, and -2 indicates a decreased firing rate in response to energy. Using this particular cell as an example, the derivation of edges and contours from an intensity map becomes quite simple.
A piece of the input to the ganglion cells, representing the differing intensities of light falling on the retina, might be represented as a string of numbers (smaller numbers representing lower intensities, and larger numbers representing higher intensities), such as this:
3 3 3 6 6 6A ganglion cell with a receptive field of +1 -2 +1 would "read" the first three digits of this series as follows:
3 3 3 +1 -2 +1(+1x3) + (-2x3) + (+1x3) or (3)+(-6)+(3), which equals zero. This ganglion cell would continue to fire at its baseline rate, having detected no change in intensity which might indicate an edge.
Given that the receptive fields of the ganglion cells overlap, a more realistic situation might be as follows:
3 3 3 6 6 6 6 +1 -2 +1Here, this pattern of light intensity is falling within the receptive fields of five separate ganglion cells, each of which will "read" its particular piece of the pattern and produce an output accordingly, as seen above. Specifically, the pattern of output produced by these five ganglion cells will be:+1 -2 +1
+1 -2 +1
+1 -2 +1
+1 -2 +1
cell 1: (+1x3) + (-2x3) + (+1x3) = 0 cell 2: (+1x3) + (-2x3) + (+1x6) = +3 cell 3: (+1x3) + (-2x6) + (+1x6) = -3 cell 4: (+1x6) + (-2x6) + (+1x6) = 0 cell 5: (+1x6) + (-2x6) + (+1x6) = 0Therefore, a pattern of light intensity that looked this:
Will be transformed into ganglion cell output which looks like this:6| _________
| |
| |
3|_____|
|_______________
This disrution in the ganglion cell frequency of firing indicates a point of change in intensity, or a probably edge in the world. These cells cannot detect gradual changes in brightness, nor do they give any information at all about areas of same intensity.|
+3| /\
|_____/ \ ______
|____________\ ______ /______
| \ /
-3| \/
|
As a final note, it is important to consider in understanding edge detection that the receptive fields of ganglion cells come in different sizes, allowing for varying degrees of resolution. That is, cells with smaller recptive fields are often more precise in detecting sharp edges, whereas cells with larger receptive fields are able to detect more blurred-over edges that cells with smaller receptive fields cannot detect. These cells with differently-sized receptive fields work simultaneously to produce a full primal sketch that contains "the best of both worlds."
Wonderful summary, along Marr lines. Which are useful, but leave out an argument which says this way of doing things actually makes sense in some worlds but wouldn't in others. To put it differently, the lateral inhibition network actually ADDS information to the picture in one sense (this is THIS kind of world), while subtracting it in another (ignoring the slow intensity variations). Did you try the simulator on the website? It is set up exactly like your example. PG
Night vision gear or Thermal vison gear shows us a picture of reality where certain aspects are amplified. Small differences in temperature are amplfified and then turned into different colors, or very low levels of light can be amplified by Night Vision goggles. It would seem that our visual sensory apparatus does a similar thing, preferentially highlighting edges, or being highly sensitive to motion in the periphery, or looking for different patterns or shapes. Because we have no experience seeing any other way, we are generally unaware of our biased vision.
While our ganglion cells are not good photoreceptors, but are good edge detectors, there must be parts of the eye and brain that receive more accurate details, at least from the fovia, right? Intuitively, I believe that my visual sensory apparatus sends a pretty accurate picture of reality to my brain. It only seems to have problems in special contrived circumstances.
the edge effect occurs at the level of ganglion cells. It is a sensory wiring effect, rather than a processing effect. Do other quirks of vision occur at high levels?
Can we do single cell recording simultaneously from all the cells in an entire nerve, say, the Optic nerve? What if we have a good idea of the part of the field of view that each neuron is recording from, could we recreate the image on a screen? What is the form of the visual information at the point when it leaves the eyeball in the optic nerve?
A pattern of action potentials in lots of gangion cell axons, of course (beginning from your last question). And yes, we could try and infer what is being looked at from the pattern of action potentials, but it would yield lots of different possible pictures instead of a unique single picture (you see why? and that the rest of the nervous system faces the same problem?). IF we could record from all of the axons (there are too many for any existing or currently imaginable technology).
Are you sure you want to argue for a sharp distinction between "sensory wiring" and "processing"? How are you going to make it? Its all patterns of activity in neurons. But, yes, there are additional edge effects more centrally in the nervous system. And yes, there are differences between ganglion cell responses centrally and more peripherally, but lateral inhibition (to varying degrees) is present throughout the retina.
Now, IF all this is true, and IF we are "generally unaware of our biased vision", and IF showing all this is easier in "special contrived circumstances" but applies more generally (which it does), what is the basis for your intuitive feeling that the visual apparatus "sends a pretty accurate picture of reality to my brain"? That's not a trick question, but rather one worth thinking about and trying to generate an answer to. PG
In class when we were discussing the neurolgical aspects of vision we concluded the human sensory devices for vision were designed to notice "edges"; sharp changes in light intensity. This explains why many optical illusions "fool" the human eye. My question is the following: what would happen if one took a had a long strip which was black on one end and VERY gradually lightened until it was white on the other end? At what point would the eye register the change in light intensity? From what we have learned so far it would seem that one would not register the continueing change, but instead would register a series of small rectangles each lighter than the next. For example, the eye would register black until the change in intensity of was significant enough for it to register a lighter shade. Therefore one actually "sees" an area of black where it actually is getting ligher but the change is so subtle that one cannot tell the difference. From the series of rectangles the brain would then be able to contruct a picture of a strip that is gradually shifting from black to white.
Nice question. Try looking at a wall sometime, with ceiling lights on. There's more light reaching your eye from the top of the wall than the bottom (since its closer to the source of light), but you don't notice that (normally), and instead see a homogenous wall (NOT a series of step changes in brightness, since no edge detectors are activated). That help? But yes, the question of how rapidly a brightness change must occur to be detected still remains (as well as the question of how come you CAN notice the difference in light intensity on the wall if you "pay attention to it"). The answer is that not all ganglion cells are SHARP edge detectors. There are also ganglion cells which respond better to slower changes in light intensity (and even, in some organisms at least, some which actually DO, more or less, report local light intensity). PG
I am skeptical in believing that my sensory input is not a true representation of reality. I certainly see the point with our brain filling in the holes that result from the optic nerve. And to some extent, what is filled in is not true. But neither is that part of our vision a primary source of input, and so it cannot effect how we see things in our brain so much. How about if we just say that our brain is "smart"? It is able to compromise when it does not have complete sensory input. Of course, there is a limit to our brain's self-smartness just as there is a limit to our intelligence. The two are of different type. Either way, I think that we are living in a real world and what we "see" is reality.
The whole checkerboard example is sort of playing with me. We have not finished our discussion on the topic yet, but as of now, we have not really explained how we see. See as in not just borders and changes, but putting all of that together and making an image of an object in our brain that the I-function can understand. I assume that the I-function is going to have to come in at some point. Not for all of our vision, but when we are trying to look at something specific. We will find out, I suppose.
Your intution is correct; we will (of course) find an I-function lying around somewhere, but not (by any means) everywhere. Your skepticism is also appropriate but let's see whether it wanes as we go on. The blindspot is much more typical of how sensory systems work than you may suspect. Yes, the rest of the nervous system is "smart", but whether that gives one (ever) a "true representation of reality" is a totally different question. In any case, your input is NOT a "true representation of reality" in lots of important senses. Which leaves an interesting, appropriate, and answerable question: why do you think that you are living in a "real world" and seeing "reality"? PG
The sensory side of the nervous system is disturbing in that it creates a reality for the individual which is not the same as the true reality. For example, when there is a lesion in the parietal lobe (which is known to occur in patients suffering from a tumor, stroke or other cerebral vascular accident) they experience hemineglect in that they will not and cannot admit to having a side of their body, normally the left side. In this case the patient will comb their hair on one side of their head, apply lipstick to only half of their lips, etc. Clearly their perception of themselves is not accurate in the sense of onlooker's reality. Similarly, every human can only detect certain frequencies of sound, light etc. Just because we can only detect the certain frequencies, commonly we believe that these are the only frequencies that exist. But with the aid of technology we can detect things that before did not exist for us. In this sense we are uncovering the true reality of our environment. On the other hand, we can never know the precise true reality of the environment because there could be a different thing similar to light or sound but different in that we have no perception of any of its frequencies. Therefore, we can never uncover this portion of reality as we have no perception or awareness of any sort of its existance. Thus, we can be sure to never know what true reality is. This is especially disturbing because it means that the brain is responsible for creating what an individual thinks is reality although it is not an accurate reality.
Alternatively, one might think of it as exciting, enfranchising? Along this line "true reality" might be thought of as an idea created by the nervous system rather than something definite out there. And then what one has to do is not to worry about whether what one sees is "true reality", but rather to enjoy finding new things that one didn't know about before. Even without a "true reality" one can happily go about creating a better and better one, no? PG