Topic 7: How close to reality is what one sees, and how come the brain does it that way?


First of all, the question "how real is perception" presupposes that there is in fact something "real" for perception to correspond to, which is debatable these days for many people. I'm not sure that this philosophical issue can really be separated from the "how real is perception" question, but it can at least be temporarily ignored.

There are some cases in which we can compare a "real" situation with a perceived situation objectively and experimentally; for example, the observed "filling in" of the blind spot or an apparent motion experiment. Both of these setups produce subjective experiences that we know to be incorrect descriptions of reality. Also, the observations of quantum mechanics (that, in many cases, a system's state seems to remain indeterminate until a measurement - or observation - is made) have suggested to many theorists that our common sense descriptions of reality are not quite good enough. In quantum mechanics and in the experimental cases mentioned, the prblems of correspondence with realism can be avoided at least in part by asserting that no reality exists independent of our perceptions. This doesn't seem to me to be the most appealing answer, although it has been convincingly argued.

It does seem that we have to accept that some situations exist in which human perception distorts reality. This doesn't mean that it does so in all situations, but there is really no way to prove it one way or the other. Why does the brain do it this way? In general, because any mechanism for interpreting the world must act on it in some way even if only to receive inputs, which may be enough to distort it. But what of the more obvious distortions, like filling in the blind spot or constructing apparent motion of rapidly flashed stationary spots on either side of a screen? WHy would the brain do this? IS it evolutionarily advantageous or simply accidental? Since humans must foveate a target in order to really see it clearly, and we do this constantly, the blind spot would be unlikely to matter to our vision whether or not it was filled in. It seems likely to me that such instances are by-products of the organization of the visual system.

Yep, two separate issues, both interesting (and maybe even related in a deep sense you're hinting at). Would, I think, all agree that filling in blind spot can in some cases be shown NOT to be perceiving "reality" (is worth thinking though about what THAT depends on; in essence, it is comparing one perception of reality with others, either others of other people or other's of one's own, and then defining "reality" as that which best accounts for all known experiences). The interesting hint in what you're saying is the idea that one must act on something in order to receive information about it. We tend to think of perception as a passive process leading to outputs, rather than as the consequence of an active process (which may be closer to the truth, and, if so, may be more than metaphorically related to the physicists' concerns about whether things exist in a particular state prior to observations). Well worth thinking more about. Thanks. PG


Based on an examination of sensory transducers alone, one can determine that each individual's perception of reality is lacking at best, and is certainly not "real" in the purest sense. If one is presented with a stimulus for which one does not have transducers, (i.e., exposing a human to sonar waves), the input will go undetected. That is, therefore, one portion of "reality" which is missing for that particular individual.

While no one organism has transducers for every possible type of input, it is noteworthy that the particular transducers which one has differ from organism to organism. In the example given above, humans lack the ability to detect sonar waves, but bats are able to do so. One can see this indicates that the perception of reality therefore varies across species. In fact, transducing abilities can even vary within species, as, for example, some humans are able to hear higher pitches than others. Following the same logic, reality is therefore even perceived differently by members of the same species. One would think that it would be useful to have all organisms of one species have the same perception of reality, if not all organisms in general. Additionally, it would certainly seem more advantageous for every individual to have a correct, complete view of reality. The fact that this is not so thus warrants further examination.

Everyone has had the experience of missing a word or phrase that an instructor said because they were "distracted" by, for example, trying to copy down information from a transparency. In effect, this is an illustration of sensory overload. Every individual has a finite amount of cognitive processing capability, and much of the information which exceeds this amount is lost, like our instructor's words. The phenomenon of "distraction" would therefore be due to directing what is available of one's cognitive processing capability to a competing, perhaps more salient, input. The nervous system compensates somewhat for its cognitive processing limitations through the automatic processing discussed in the previous essay, (in which the nervous system gleans some information without "you" needing to consciously attend to it), however a great deal of potential input is still lost.

Given that one is incapable of processing all of the information for which one has transducers, one can see why it would be not only impractical, but also potentially detrimental, to have transducers for every possible type of input. The fantastic amount of information which would bombard the system would probably impede meaningful processing, and might result in the loss of information important to survival (i.e., not seeing a sabertooth tiger that is about to attack). As a result, it seems logical that the nervous system should only attend to the information which is most relevant to the organism, and would therefore only need the transducers for those particular types of input. As bats are nocturnal creatures, their ability to receive and interpret sonar waves is adaptive for their navigation in the absence of light. Humans, conversely, function more during the day, therefore sight ability is more appropriate. One could therefore argue that those types of transducers which each organism has are the ones which are most useful to the organism's specific niche, and it lacks the others because they are not immediately relevant to the organism's survival.

Fair enough, as far as it goes. But how about the legitimacy of "making things up"? And, maybe even more important, would it REALLY be advantageous if all individuals and organisms had the same perception of reality? Does anyone know enough to design a system to give a "correct, complete view of reality"? How do the answers to those questions relate to one another, and what follows from it? PG


To start I would be greatly interested in reading about how athletes train as it involves the brain. As you may have noticed I get much more excited about a concept when I can relate it back to something I personally do. Not that crickets aren't interesting but I haven't been listening for mating calls lately.

Going on to the question "How real is perception?". This immediately hits a problem, what is reality? Who is to say what is real? With that in mind I will try to answer this question as I see it. Perception is completely real, but it isn't complete. We, humans, percieve the world differently than bees because they have transucers we don't and vice versa. Neither is wrong, we are both just getting a different set of inputs. More complicated than this is that differnt individuals within a species can percieve the world diffently. Using humans again we know that we all have varying levels of eyesight, touch, hearing etc. This will make no difference as long as we all use the same set of words and concepts. What I see as green and what you see as green could be two completely different things but that is OK because when we see that color we call it green and that will correspond to what the other person saw as green because when we were young we learned that when we have that input we call it green. Although this makes it difficult to say what is reality because everones is different this system allows our anatomies to have slight differences without causing major problems. Let me try to explain what Im saying. If there was a "true" reality which a couple people could detect then for everyone to be able to communicate and live together we would have to all be able to see this. Yet even identical twins are slightly different so perhaps one had a few more photoreceptors than the other. Suddenly there realities would be different. If there was zero difference in our bodies than perhaps a stagnant reality would be possible. Another problem with that idea is that, as we saw before, the same input hardly ever results in the same output. There are too many factors involved in the brain to always have the same sense of reality. Michelle K. Bostick

Don't worry. That's the way its supposed to be. No one gets really excited about things UNLESS they have some connection to their own lives/experiences. And now a confession on my part. I KNOW there is a literature based on athletic performance, but I don't have an entree to it at my finger types (the embarassment is that I should, since it is something I get excited about). Stop by some time, and let's see whether between us we can find a way into that literature.

Perception: sure, different transducers in different organisms, and in different people. Interesting thoughts about how to view those differences. One way, you're suggesting, is to think of them as a problem, and hence to presume they are small and don't make trouble. An alternate possibility we'll explore from several perspectives is that they are not so small after all, but rather than being a problem they actually constitute an advantage: assuming there is some way to share the different perspectives on reality which different people (and organisms) have. PG


"How real is perception, and why would the brain have us perceive this way? Why don't we have a 'better' perception of reality?"

Our perception seems to depend solely on what our sensory neurons can sense. Their transducing capability, their ability to transform an input signal to an action potential, the common currency of the nervous system, is the determining factor of what information comes into the brain. Obviously we have limits to our sensory capabilities; we can not hear dog whistles, nor can we sense magnetic fields, for example. But that does not seem to be a disadvantage to our day-to-day functioning. We can get along perfectly well with our "limited" five senses, with the limits of the sensory transducers of our human nervous systems. So although our perception of our world is not complete, I don't think it has to be. However, isn't it funny that the "progress" of human kind has included the manufacture of man-made devices to perceive phenomenon in the world that our human senses do not: Geiger counters, infared photography, for example.

Then we must take into account the fact that the brain "invents" a reality for us. Take for example the reality we perceive while seeing. Because of the placement of the optical nerve in the eye, there is a place in our retinas where there are no photoreceptors, sensory neurons which perceive light. So, there should be a hole in the picture we see in our heads caused by this lack of sensory input from the hole in our retinas. However, we do not see holes in our sight perception of reality, in our heads we see a complete picture. The only explanation for this is that the brain fills in the holes with made-up data based on input from the large number of photoreceptors around the hole in the retina. In a sense, we have a mechanism in the brain that has an ability to lie to us, to fabricate reality for us. Is this the same mechanism that allows us to lie to ourselves about other aspects of reality, like the blindness we have to the faults of our loved ones? It could be thought of in a more positive way; it is not a mechanism of false fabrication, but the mechanism of creativity that the brain is using. Somehow, even at a basic level of sensory processing, sight, there is a mechanism that also provides us with the ability to imagine, to create, to invent machines which can sense for us the phenomena we are not capable of sensing.

So it seems that we have just the basic sensory power that we need. But that there is also a mechanism that fills in the holes by using information provided by our five senses. Would a better, more complete perception of the world lead us to be less creative?

You DO come up with some interesting perspectives/questions. I'm not prepared to give you that we have "just the basic sensory power that we need". In part for the reason you mention, something is certainly driving technology to increase our transduction capability. And in part because trying to understand biological systems in terms that what they are is what they need ends up being circular and not very productive. And, in part because, as you say, we actually "create" when things are missing. Now, where you surprised me is with the suggestion that our inputs are less complete in order to assure we are more creative. Very interesting thought, but it presumes we COULD be complete and therefore not need to be creative. I suspect the reality here (as in many things) is that neither we nor anyone else knows what it is to be "complete", and therefore both incompleteness AND creativity are inevitable. PG


The question regarding the soundness of the present anatomical arrangement of the eye in regards to neurons is indeed an intriguing one. For instance, one wonders why the retina cannot be just one big foveal area, or a substantially larger foveal area, in order to increase the amount of visual accuity and presumably efficiency. Further consideration seems to imply that an arrangement of this sort would greatly increase the amount of sensory input traffic, necessitate the enlargment of the entire eye, not to mention increase the total amount of energy utilized by the nuerons associated with visual processing. An analogy of this situation can be found in the eyes of birds of prey in which the anatomical structures of sight compose roughly half of the brain mass. Based upon the lifestyles of humans, this sort of sophisticated visual processing is unnecessary and energetically unfavorable. The current structure also appears more evolutionarily favorable considering the ways in which our eyes change as we age. Keeping in mind the gradual hardening of the lens, atrophy of eye muscles, increased difficulty with focusing, etc. the smaller fovea appears to be a sounder option than the more energetically taxing alternative.

In a similar manner, the aging of our eyes also lends itself to our perception. The reliabilty of perception is dependent upon a variety of input. Aspects of sensory input such as light placement, shading, perspective, the relation of one object to another, and stereoscopic cues all influence the image that eventually is produced in our mind. A fascinating phenomenon is the ability of the brain to formulate patterns from a seemingly random sensory inputs. When one considers popular 3-D "Hidden Pictures" that rely on the brain to locate the image from amidst a colored pattern by distinguishing small regions of high contrast, we can easily observe how finely tuned our eyes actually are. The need to quickly locate a coherent pattern makes sense upon consideration of the ways in which our eyes change as we age as mentioned above. Detection of patterns becomes finely tuned when our eyes are young and enables us to quickly detect the similarities in patterns later on as the eyes age.

However, one must also realize that perception itself is is to some extent predetermined by our minds. Support of this comes from studies done with individuals that were born blind, but have since had their sight restored. One subject remarked upon first seeing her reflection that she always thought she was better looking. Another said that she had alway thought that trees and humans looked alike based upon the simliarities in shape between the trunks of the trees and human torsos. This indicates some degree to which the brain forms connections which affect the perception of reality.

Some interesting connections in several directions. I'm not sure though that trying to figure out what is most efficient (energetically favorable) is the best way to explore the issues. Different organisms do things differently, and the same organism differently as it ages, so presumably all ways of doing things are in some sense equally successful in one or another context. Yes, popular 3D pictures do depend on high acuity vision (among other things), but that isn't inevitably or necessarily better when young than when older. The issue of how much of what we see reflects inbuilt processing as opposed to prior experience is an old and fascinating one, with a large and still growing relevant literature. Let me know if you'd like to get into it, and I'll suggest some places to start. PG


This past week in class we discussed visual perception. One very interesting feature of this process is that images as seen on the retina differ from those in real life, and the image as perceived in the brain can differ from both the retinal image and the real world image. For example, there is a spot in the eye where the axons of the retina's ganglion cells leave the eye to form the optic nerve. This spot has no photoreceptors, and thus there is a whole in the retinal image of the object being perceived in this location. The brain, however, does not perceive the object as having a "hole" in it, but instead fills in that "hole" as it believes it should according to contextual cues.

The result of this process is that the brain may perceive the proper image, or it may make a mistake and perceive it incorrectly. If the incorrect image is the one that the brain adopts, perception is not real.

This is no big surprise, that perception is not [always] real. When five witnesses are questioned about a crime, seldom will the police receive five identical reports of what occured. This is due to each person's brain perceiving the events a bit differently. In such a case, the police officers have to act as the brain and piece togther what really occured; like the brain, sometimes they will be correct and other times they will not be.

There are drugs that can influence the brain in such a way as to throw perception WAY off. A person on an acid trip may see hands coming out of the wall when no such event is occuring. This is called a hallucination.

Why would the nervous system be structured in a way that allows hallucinations to occur? or even the minor mis-perceptions seen visually? I believe that this is actually meant to be a benifical aspect of the nervous system. The nervous system gathers input from many arenas--both eyes, both ears, the other senses, memory--and coordinates the information to create the picture one perceives. If perception were only based on information coming from a single eye, then the brain could not create such a detailed image. Only when the input gathered from the various arenas dod not compliment each other does the brain need to decide what is and is not real. Drugs mess up this process and create hallucinations, but on a normal daily basis, the brain usually does a preety excellent job

Very interesting, appropriate thoughts. So why hallucinations (and, more generally, making things up)? You're ALMOST there (where we're going), but then you backed off a bit. The argument is need lots of things to make "detailed image", and therefore disagreements, and therefore need to make things up? Interesting, need to think more about it. Let's see how close it is to where we end up in class. PG


How real is perception and why would the brain do it this way?

This is a topic which I have once encountered in a completely different context. I was thinking about modern art and, in particular, what can be the idea behind abstract art or even cubism. Then I thought that maybe what we perceive is not the reality around us - it is one version of it. Maybe if we had our eyes 10m apart, our surroundings would look very different.

Next related thoughts came in my math classes when I moved to the world of higher dimensions. Ofcourse we can only perceive 3 dimensions, but it is an accepted fact that there is more to the reality than that.

But what can we really say about the reality? We can only base our judgements on what we perceive, either directly, or when mediated through scientific detection. At the same time, we can not be sure about what is really going on.

We have talked about many examples of things that humans can not perceive. We have proven that our perception is only a subset of reality and that it varies even within the human kind. I have always been very reluctant to accept people with Òspecial abilitiesÓ and qualified them as not scientific enough. But each one of us has our own world we live in and although our perceptions fluctuate in a relatively narrow range, there can be substantial differences between individuals.

This whole topic of perception seems a bit depressing to me since it replaces the reality with something very subjective and unsure. That brings me to the second part of the topic: why would the brain do it this way? It seems that we are simply spared of the information we do not necessarily need for survival. We do not need the ability of perception of electric/magnetic fields for our life - fish and birds do. If we think about the issue in terms of evolution, our sensory organs were developed the way we need them. If we were able to perceive more then we need, then our perception would not be as focused as it could be. Moreover, I believe oneÕs perception is influenced by environment and training. I once read about people who live in the forest all their lives and when in an experiment one of them was taken out to the planes and could not judge distance very well. Objects that were far away just seemed small to this person. Is it because the corollary discharge assiciated with focusing on certain distance did not function well?

I'm not sure, but its an interesting issue, and there is a large and fascinating literature on visual perception in people with various kinds of restricted visual experience. The connections to art and math are worth following up on. As for the depressing, yes it is appropriate to think we have less and more individualized access to "reality" than one might have thought. On the other hand, there are reasons for that, and some real benefits. If you're still depressed after next week, let me know. PG


In my oppinion, what we perceive as reality, is reality. If we were to video tape everything in a day (get a machine recorded display of reality), I would bet that it was no different then what we saw with our own eyes. Maybe we could notice things we had not scene before, but I feel the blind spot in the eye would not at all change how we saw things.

Reality is such as abstract word, it is very hard to define. I feel that "reality" is different for every person. You and I may not think that UFOs are part of reality, but to someone how claims they saw one, UFOs are very much a part of reality. It is not really fair for us to judge what someone did or did not see. There is so much that goes into interpreting the different inputs into our brain, one stimulas may illicit two very different, very correct responses.

Say for example you say something to me. You might know you are joking or being sarcastic, and that is reality to you. But if I did not know you were just being a wise guy, I would think what you said were true, and it would become part of my reality. Or another example, you might see something and because of something that happened in your past, interpret it one way, while I might interpret the same thing very differently. It is a hard concept to explain (and I'm not doing a very good job of it!)

Why the brain does it that way is a very difficult question. For what ever reason it does it that way, it obviously works. Despite a blind spot in the eye and different views of reality, humans have survived.

What you said in class about not everything having a reproductive advantage really struck me. When ever I heard about some odd quality of an organism, my first reaction was to try to come up with a reproductive advantage, but what you said changes my ideas greatly. Its like the more I learn about the human body, the more amazed I am by it. I am reminded again of the question of is there a god? It is something I have been thinking a lot about, and the fact that the body IS so complex and delicate, that makes me think there is one. The odds of life ever forming, serviving, and turning out the way it did are so remote, there must be something greater. The system of checks and balances is so delicate.

Very interesting/intriguing, both the immediate response and the extensions it takes. I share your sense that inputs do not determine perception and your examples are good ones: the "reality" of any give thing can be quite different to different people. Hopefully, the blindspot and related things will help explain WHY that it so, and hence make your belief more certain. But that begs the more difficult questions: IS there a reality? and how come the brain deals with it the way it does? Yes, of course, it WORKS. Whatever is alive represents something that works though and so that doesn't provide much explanation for why a PARTICULAR thing is the way it is. Maybe there are some other explanations for why things like the brain are the way they are? God (or gods) are certainly one possibility. But maybe there are others? Perhaps others that might account for why the brain sees things they way it does? PG


some thoughts on perception

It is slightly disturbing to think that what our brain sees is not what our eyes see. The way vision and perception is organized in our bodies is obviously quite reliable yet the inconsistencies it creates are odd. The brain, in the case of vision acts as translator of sorts for the signals coming from the retina of the eye. I have found that in many cases that the signals travelling from the peripheral organ or section of the body to the brain are not directly processed by the brain and that the chief role of the mass of neural tissue in our skull is to translate signals into perception for the I function. This is so WE are able to percieve the wide range of senses we do.

The difference we see between the image on the retina of the eye and the image the brain creates is one of the fundamental mysteries of the brain that we do not have an explanation for. We know the mechanisms involved in the transduction of a signal along the length a nerve down to the molecule. But at the critical point where the signal becomes perception there is no explanation as of yet. Perhaps it is better to conserve this mystery. It is however clear that this section of the brain can be adjusted and it's translation mechanisms rearranged. Through chemical alterations caused by some drugs, hallucinations in the visual perception occur. This is an example of the brain creating an image all by itself without input from the retina. So yes, I feel perception is real but I can not say that with great confidence, because as of yet I, like others do not know how it works.

I'm a little puzzled. You really want to "conserve this mystery"? And really think what you perceive is "real", given both the blindspot AND hallucinations? Yes, indeed, there is a special step involved in what *I* see which we haven't gotten to yet (and will), but it seems to me that along the way we're in fact getting some important parts of the mystery clearer, no? PG


How real is perception and why would the brain do it this way?

As already stated in class we would only have access to those aspects of reality for which we possess transducers. There are many aspects of reality that we do not have transducers for; such as radio waves; a large portion of the electromagnetic spectrum and so forth. This in itself already cuts down reality or how much of it we perceive in our lives.

A section that we have not yet addressed in class is the role that memory plays in perception. This I think is an extremely important part of the puzzle. When we are in a region that is very familiar to us, we (or at least I) find that when I switch off the lights, and the room is quite dark, I am still able to find my way around very efficiently and I am even able to find specific things in my room without really seeing them and even do stuff. This is an essential part of perception. This ability of ours/our brain, implies that there is a great deal of what we see enters our memories and the brain is then able to recognise these things when seen again and even when not really seeing them, send information which is fairly accurate to other regions of the nervous system and enable us to do things working from a picture in the brain. For example, when our vision deteriorates, and our lens does not maintain its ability to bend light coming from different distances very efficiently, sometimes, before we do anything to remedy the situation, we are still able to recognise objects and people when seen at a distance. This means that although what we see (reality) is impaired somewhat, our brains are still able to recognise whatever we do see and in a way, put the different pieces together and provide a conclusion - sort of like with the blind spot experiment...the brain fills in the blanks. Another thing though, is that I feel that perception of the world not only involves information from the eyes but also from all our other "senses" such as touch, smell, hearing and so forth. Information from all these regions must also be recorded in the memory and work to improve our sense of perception and make it as real and accurate as possible.

To what extent do blindspots affect our perception of reality? When we have information coming from both eyes, the brain is able to take these different pieces of information and interpret it for us. The effects of the blind spots is usually cancelled out when we think that light from a source does not usually hit the same region on both retinas. However, how much does it make our perception unreal if we are blind in one eye? For those who are blind in both eyes, how real is their perception of the world and how does this differ for those who are born blind and those who become blind during their lifetime?

I am still not sure if I understand the correlation between viscious animals and eyes in front of their heads and herbivores/gentil animals and eyes on the sides of their heads. I was also curious when thinking of animals with eyes on the sides of their heads. It must not then be possible to see (to a certain extent or within a certain range) directly infront. Although the brain is receiving information from both eyes (each with a different view of the world) there will/should always be a region missing in their picture, where neither eye sees a particular region directly infront. Is this true and if so, how does the brain deal with it as this is some important info that is missing? Does it simply fill in the blanks like it does in the case of blind spots, using information from the surrounding areas to complete the image? Would this be a very accurate method of perception?

When we see something, we only ever receive a segment of the entire picture. For example if we see a man, and behind him at some distance there is a tree, we will not be able to see what is between the man and the tree. The light coming from the sources in this region is being blocked off by the light being received from the man, i.e. what is being interpreted by our brains of what could be in between the man and the tree may not be entirely true.

The main reason I can think of why the brain would use information from surrounding areas to make a picture in our mind complete is for mere survival. It would be very confusing to leave regions of the image which correspond to light falling on your blind spots as mere holes and more often than not, the consequences of the brain doing this are not detremental and accurate enough to enable survival. The brain works in the most efficient way possible when it combines information not only from both eyes but also from other sensory organs to perceive a sense of reality which does not seem to be far off - but then we really wouldn't be able to tell since this would be the only reality we know. If it enables us to survive successfully, then its all we need.

Extensive and very rich set of thoughts. I agree very much that the way the brain "sees" uses prior experience to fill in uncertainties, much as it uses other information to fill in the blind spot. And it does, at least in some cases, do the same thing with bigger blindspots (remind me to tell you a personal experience with a migraine attack; despite lacking any (known to "me" information about anything to my left, I was unaware of any holes there until the picture and my memory didn't match). All of which says that how the brain works "enables us to survive successfully", of course, but says something much more specific as well, which you're suggesting and we'll get to more in the course: the picture we have is much less dependent on input than we usually think it is, with the input serving in many cases not to create the picture but only to check it. And that in turn does indeed raise some very interesting questions about sight in people born blind. PG


It was said in class that our perception is very different from reality, and that what we see is not necessarily what is. This has been sufficiently supported to be considered true, but the question of why the brain doesn't represent the reality as it is probably doesn't have a clear answer. A partial answer for the question of why our perception of things is so different from reality is probably contained in the complexity of the processes by which we are allowed to see.The phenomenon of vision involves complicated interactions between our eyes -- which are very elaborate and precisely organized organs, between eyes and brain, and between different "boxes" in the brain. Since it is the case that many of the intermediates involved in seeing are probably themselves multi-leveled, the complexity of the system further increases, and therefore there must exist a sufficient number of places in it where small errors can easily appear. These deviations would account (at least to some degree) for the discrepancies between our perception of reality and the reality itself. I have heard a curious theory that ElGreco, an artist who always drew people of slightly elongated shapes and with very oblong faces (I'm not sure when he lived late 1700's?) drew like that because he had a problem with his vision: to him, the reality was always a little stretched. Another example demonstrating that the image we get doesn't necessarily correspond to reality: brain completes the images from the eyes' blind spots by taking information from other spots around it, so we can not really be sure whether the whole picture we get is what it is in reality,( though probably because we constantly move our eyes, the picture is always being updated and is not too unexact). The triangulation of the points of light to produce 3D images also requires great precision and so any small mistakes and deviations would also likely affect the perception from reality. To come back to another question posed at the beginning, I don't know whether it is possible to answer the question why the brain gets the images from the outside in the way it does. We know that it is quite efficient at it however, and then I don't know of any alternate ways in which images could be obtained -- the eyesight of other animals is different ( in some ways less advanced), but it is well suited for what the organism needs. Sorry about the sketchy thoughts, I wasn't in class on Thursday, and I'm not sure about some of the things in the notes.

No problem. Interesting thoughts/questions nonetheless. Yes, its certainly possible that what we see differs from reality because of the complexity of the system and inevitable associated errors. BUT their are some pretty systematic distortions of reality going on, which suggests something other than random errors. Of course they system is "good enough", since we are alive and use it. But could it be better? And how would we know how to make it better? And what about those systematic distortions? Let's see if we can come up with something that connects all of those questions. PG


In my opinion, perception must be very different from reality. According to the dictionary, perception is a way of understanding or seeing, and numerous real-life situations show that people perceive things differently. For example, when a pickpocket is seen taking a wallet from someone's purse in the mall, most of the accounts of the incident from various witnesses usually differ. It is odd that the descriptions of the perpetrator would vary (in hair color, height, clothing, etc.), because the crime was committed by one person at one time. Yet it seems as though the witnesses believe that what they saw was what actually happened. Therefore, what each person perceived could not have been reality, but rather their perception of reality.

In class it was mentioned that in making a picture in the head, the brain makes up part of what we see to complete the image. The brain is able to guess what belongs in certain blind spots based on the light inputs from the surrounding areas. Therefore, this may play a part in how people can perceive the same thing differently. Maybe their brains process the neighboring light inputs differently and predict different images (or a part of an image) to fill into the picture in the head. Furthermore, it could be that people may perceive things differently due to their individual experiences. So, perhaps when we catch a glimpse of something, it triggers our memory and causes us to relate the image to a particular picture from a previous experience. Then what we briefly saw may be somewhat influenced and altered by the memory, distorting reality. In that case, the person's reality would change based on the interpretation of what they think they saw.

As I was writing, an interesting point occurred to me: Since it seems as though people perceive things differently and that one's perception is one's reality - what that person believes to be real - more support is given to the argument that the brain is behavior. Everyone's brain is different, leading them to interpret what they see differently. And because they perceive things differently they behave accordingly, which is also varying. Therefore, it follows that the brain would be behavior.

So, maybe the reason why the brain perceives reality differently is somehow related to behavior. Or maybe due to the limitations on the wavelengths of light that we are able to detect. I don't know, but I hope to find out.

A wonderful extension of things said in class to the "real" world. Of course eye witnesses may "fill in" differently and hence come up with quite different accounts of the same events. Raises some interesting general issues about the usefulness of "eye wittness accounts", yes? And an intriguing point that popped into your mind as you were writing. Indeed, we DO expect people's behavior to be different, and if brains are too that does indeed help make the brain=behavior argument more solid. Thanks. PG



For the last week in class we have discussed the anatomical nature of vision. Moreover, we discussed the ways in which certain structural entities in the eyes corresponded to certain functions. The first step in the process of eyesight is the creation of an image in the back of the eye, this image is then modified and appears to us as reality. Special attention was paid to the actual image which is created on the retina as a result of lights rays being curved by the lens. The image created on the back of the eye is different than the image we carry around in our heads in a number of tangible ways. First the image on the back of the eye is two dimensional whereas the image in our head obviously is three dimensional. There exists a blind spot resulting from the anatomical composition of the eyeball, nevertheless no evidence of this hole can be found in the images in our heads. The question we posed at the end of the week was to what extent is the image we see in our eye reality. This is essentially a philosophical problem which has troubled minds for thousands of years. From a purely pragmatic standpoint what we see in our head must correspond to some sort of reality, for we know if we see a car quickly coming at us, if we didn't move, we shall die, but if we do move, we won't. In this line of argument it could be asserted that everything we see in distorted but if that is the case, we are still distoring everything in a uniform was, and it really doesn't matter for this is all relative. This line of reasoning is analagous to the statement you made to Rufus when he claimed the image on the back of our eye was inverted. The small adjustments the optical apparatus make, probably do not differentiate much from reality anyway. For all intents and purposes the area around a certain object(which our mind convienantly fabricates based on the surroundings) is probably quite similar to what actually exist. Although not an exact presentation of reality, it is close enough and anyway, it is much less distracting then a big hole in our view of the world.

Fair enough. And of course the issue of "reality" has been around for thousands of years. But I'll try and persuade you you're minimizing the significance of the kind of making things up represented by the blindspot, that its actually a much more pervasive phenomenon, and that recognizing that does in fact help to sort out some of the issues that have been around for a long time. Let me know if we don't get somewhere along those lines. PG

Follow-up comments:

Another thing I was thinking about has to do with how well the world we internally perceive corresponds to the actual world. When we were discussing the fact that humans, as a species, only have sensory transductors for certain ranges of light and sound and who knows what other mediums, it appears as if the world we perceive might be completely different than the world as it actually is. Moreover, it seems very unlikely that we will ever be able to construct a word of reality even in the abstract sense for one can not describe what one does not have experience with.

Yeah, but maybe there are ways to GET that experience? PG


Questioning the truth in reality and perception is something we do everyday yet it is another idea that is impossible to determine a specific answer/explantion for. In general, we have grown fairly accustomed to what we supposedly can see though there is always that inherent question of whether or not what we perceive is really what we are looking at. What I think makes the questioning of perception the most interesting is the part of the I-function in it. I mean the brain is not exactly seeing "green" because green is a color someone's I-function assigned to the grass years and years ago. The fact is some of what we consider real and what we call what we are seeing are fabrications of someone else's perceptions that have become ingrained in society.

However, just the way we see, how the brain actually enables us to look at objects in the distance and recognize what the object is seems to be a fairly simple process. The idea that what we see is dependent upon how far away the object is makes sense since it would be impossible to see inifinitely. However, the way that the optic functions of the brain actually performs the differentiation (by bending the light source too much, the rays will cross so that the point of light on the retina is an infinite pattern) seems a little surprising because it sounds too simple. Reality seems like such a complicated notion yet much of how the brain seems to let us perceive/see seems straightforward. By triangulating images in order for us to see depth seems like an ordinary geometrical notion. In fact, what is very interesting about a so-called 3-D movie is that without the glasses, the pictures on the screen are fuzzy, with an outline of red and blue around each. Due to these outlines, when the glasses are worn, the glasses will help to triangulate the images; therefore, we think the people on the screen are moving toward us.

Got the idea that what we see might be "made up", both by others and by ourselves, yet what the brain seems to do is "simple". Assuming brain=behavior, what it is to "see" and what the brain does must be the same thing. Can think of ways what the brain does can be shown to be "made up"? And ways in which the "simple" things the brain does might yield something more like "seeing"? PG


We have established that visual perception is not related to reality to any great extent. The image that one holds in one's head is not the same as the image that lies on the retina. It appears that the brain does quite a bit of creative work in generating images from the information provided by the retina. For instance, the brain fills in the blind spot where the optic nerve interrupts the retina by using the images on the retina near the blind spot. In addition, the construction of the cell layers in the eye seems counter-intuitive. Light enters the eye and has to go through two cell layers before it reaches the photoreceptors - the area at which it is first processed. After processing there, the signals are passed back out to the two cell layers which were in the way earlier. The next question to ask is why.

Why are the photoreceptors in the back? We discussed the point that what we see now has survived through evolution, but that survival is not really such a feat. If the organism can see well enough that it isn't killed too easily, the features of the visual system will survive as well. Perhaps the photoreceptors are in the back because they were the first layer of vision cells. Perhaps early organisms didn't have middle nuclear and ganglion cells because they didn't need the level of visual acuity or the color vision that we have today. Perhaps the additional levels of cells developed later, and thus grew out, like specializations of the photoreceptor cells. AT any rate, the visual system has made accommodations so that the distortion caused by the cells is compensated for, so it is likely that the whole system works well enough.

Why is each point in the image determined by many points on the retina, rather than just a corresponding point? This makes sense in that the image in the head will not be distorted if a particular photoreceptor or the cells at a point on the retina are damaged. The brain, by taking a sample of surrounding cells, may be sacrificing some accuracy, but it is taking precautions against mishaps. Thus, if there is damage to the eye at a certain point, there will probably still be a relatively accurate complete picture in the head. Furthermore, the brain has the sum of information from two eyes to work with, and thus the chances of accuracy are increased. Thus, while the visual system is not able to produce an exact replica of the information provided by the external world, it is able to create an image that is accurate enough to allow us to function well.

Nice wrestling with some questions. "Works well enough" is true, but careful, it sometimes ends thinking about questions prematurely. As for the business of using lots of retinal points to determine one in the picture in your head, your thought is appropriate in a simple evolutionary sense, but there may be a more interesting answer. We'll talk more about this in the next lecture. PG



Okay, well, first off, what do you mean when you say "perception"? Do you just mean things we percieve with our sense of sight, since that was what we talked about in the last lecture? Or do you mean perception as relating to all senses, which we sort of touched on in the tuesday lecture? I think you mean everything. We decided that sensory transduction in general is the process of using various receptors to transduce an external stimulus into something that our nervous system can use to make decisions and behavior relating to it. We also said that what is coming into the nervous system is a subset of the available information of what's going on in reality.

Maybe now I'm starting to think that you meant perception as it relates to vision. So how does the whole mechanism and process of vision relate to what we just said? Well, to see, we use photoreceptors, so that fits w/ the whole thing so far. As far as the information coming into the nervous system being a subset of the available information in reality goes, that makes sense, too. When we see, we don't see everything in the whole world, we just see a specific subset of all of that. We said in class that the area we see very clearly and accurately is a small area where the photoreceptors are packed together tightly. So far, all of that is very real. Something exists, you see it. Simple as that. But when you said how 'real' is perception, I think you meant how real is the part we make up. We did that experiment in class about holding the piece of paper w/ the 'x' and the dot and seing when the dot would appear and disappear. When we can't see the dot, we see paper anyway. This is so far away from the area that's very focused and clear, and what we're doing is actually making guesses about what should appear there based on input that's coming in from the area immediately around it, and what the light is doing in other places.

When you ask why would the brain percieve things this way, I think that question can be answered w/ one word- efficiency. Why would a rabbit need to see everything around it? It's not out hunting other animals down, so it really doesn't need to be aware of everything in front of it for survival. But eyes on the side of its head can help it see predators and get away. I guess predators would approach from the side, since charging something straight-on doesn't seem like a sly way to do it, but even if it did that, the rabit would smell it and take off. So I guess the integrated perception (including all of the senses working together) is built to take care of that, too.

Fair enough, as far as we've gotten in talking about perception. But its going to turn out that there is MUCH more making things up than one can account for so easily. Let's see how you feel in a while about the relation between perception, reality, and what animals (including ourselves) do and don't "need". PG


The in-class "experiments" clearly demonstrated the element of myth that comprises perception. While the brain receives information from one photoreceptor in a direct correlation, there is an area in the retina where there are no photoreceptors. This gap cuts the communication ink between the brain and the image falling on these photoreceptors. The picture on the retina thus differs from the picture pieced together in one's brain. This error in perception, however, is actively recognized by the brain. The brain assumes that the input from the photoreceptors around the hole is a reliable predictor of the scene that the photoreceptors are projecting. The brain assesses the outlining photoreceptors at face value and integrates their facade into the hole. This demonstrates that there are places in the picture in the head where appearance has nothing to do with the light on the retina, but rather with the light across a greater expanse of the retina. Perception is further distorted when two light sources, on the same line, illuminate the same photoreceptor. Both sources will be indistinguishable to the brain and only the light from the closest object will be registered. Every individual receives two images of the world, one from each eye. The information from the eyes allows the brain to do a triangulation configuration that helps detemine the location of the object in 3D space. While these two images overlap, creating binocular vision, a single unified impression of the world results from both views. By adjusting the curvature of the lens, the overlap is brought into focus. Reading through the bulk pack, I was struck by a number of ideas. To begin, I was intrigued by the notion of preattentive perception, in which sensory recognition of a familiar or past experience is both quick and highly accurate. This phenomenon seems to imply that certain signals can contribute to an expectation and a conclusion, by the brain, of what is triggering the cascade. Another article asserted that perception of depth is not affected y one's objective knowledge of up and down, but rather by the orientation of the object on the retina. This argument seems to return to the idea that "you" are not in the driver's seat. I wonder if visual processing occurs in a "spotlight" manner or if the entire visual field is ascertained simultaneously? Perhaps, if the situation warrants the visual framework is used. I was also wondering if neurons can be fatigued or over-stimulated and how this may adversely influence and limit our perceptual reality? Must the eyes then remain active and in constant motion in order to offer the most accurate protrayal of reality? On a similar note, I was wondering what role visual receptors play in both dreaming an sleepwalking. How is it that our sense of reality is created in these states? While memory must play a key role, how are the "scenes" created and are they dependent on initiation from visual cues or visual memory?

A whole host of interesting questions and wonderings. With some interesting relations among them. Sure, neurons fatigue, and that will affect input signals. But pictures, as you argue from dreams, aren't entirely a function of input signals (no, photoreceptors are not active). From which, it follows that ...? We'll come back to dreamsn and to the relation of all this to the "I-function". PG


I'm not sure we are equipped to answer the question "How real is perception?" As we can only attempt to answer only through our own perception, this is like using a yardstick to measure itself. The standard by which this phenomena is to be measured is the phenomena itself and thus has a built in degree of uncertainty. The question can, however, be attacked at certain angles. Having developed a model of understanding neurological activity (interconnected boxes within boxes composed of neurons as the smallest boxes, operating via patterns of action potentials), we can apply this model with its capabilities and limitations to what we believe perception to be.

From here we can speculate on how reality might differ from perception and in many cases actually observe the divergence of reality and perception. We have done this with several examples within visual perception to include how the brain actually interpolates information to fill our blind spot. A second approach to the question employs the standard of one individual's perception verses that of another's. Here too we note that a "reality" carefully engineered to be identical to two individuals will be perceived differently in some way by them.

Both of these approaches reveal perception to be at best an approximation of reality. This is before even attempting to account for any built in error associated with using perception to measure itself. It seems rather clear that perception and reality may often, if not most of the time stray far from one another. This leads us to the second part of the question, "Why does the brain do it this way?"

On one level, the answer is a simple one that has been used before to explain biological phenomena: Because it works. Our perception however divergent it may be from reality, has enabled us to achieve what we need to survive and then some (like sitting around speculating about the nature of perception and reality). Our brains have evolved by making use of a picture of reality created in terms of patterns of action potentials. Just as the limited resolution of our computer screen class picture provides us with a decent approximation of how we look as a class, the limited resolution of perception within our brains gives us a decent enough approximation of reality to find food, shelter, and avoid getting run over by large vehicles. A reality painted in action potentials may seem crude in light of what reality might be---and it probably is, yet it works.

Yeah, but what about the OTHER levels? Betcha we can do better. Even YOU think so, your essay is set up to give an answer. How come you didn't? PG



According to the article, "The Physiology of Perception," each time a particular odorant is smelled the same central pattern is formed. This explains why people often associate smells with experiences or feelings. For example, the smell of a particular perfume can be so strongly associated with the person who wears it that it forms a pattern of neuron synapses. If the same perfume is smelled elsewhere, it will trigger some of the same patterns in the nervous system and the smeller will remember the person who often wears the perfume.

When questioning perception and reality, one must consider dreaming, which can feel very real but occurs only within the nervous system. The sense of smell is sometimes incorporated into a dream. The dreamer perceives and reacts to a smell that in reality does nto exist. What starts the pattern of neurons that lead to the response within the dream? Input from outside the nervous system is not required at that particular time but it may be that dreams are composed of patterns established at an earlier time. A dream could be a variety of already created patterns that are activated for other reasons than an outside stimulus.

Indeed dreams need to be thought about in relation to perception. And we'll get to them a little later in the course. In the meanwhile, in addition to wondering about how dreams get started, what do they have to add to a consideration of the nature of perception, and why the brain handles "reality" the way it does? PG


How real is perception?

I do not know how real my perception is after learning about the picture in my eye and the picture in my head. I like to think that the picture in my head is the picture of the real world, but after learning about how my brain makes things up, I am uncertain. I find myself testing myself to see if I am truly seeing the world accurately because of this uncertainty I feel. On the other hand, I know that my mind perceives the world as it really is. When I detect a book directly in front of me, I know that it is there because I can extend my right arm and touch it. When I see a friend Sam approaching me, I know that the person is Sam and not an allusion, because I can shake her hand and hear her say hello. But how I account for the observations that the brain can fill in gaps and place things that are really not there?

Nice question. Worth thinking more about, particularly since I think you've already got two important parts of the answer. The brain DOES make things up (even more than we've talked about as yet), but it ALSO is constantly checking what it makes up (reaching out to touch the book) to see how reliable what it makes up is. PG

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