I find it difficult to understand how our sensory apparatus can have any knowledge (or even "knowledge" if that is different from just knowledge) about anything at all. I would have thought it was people who know this or that, and it is with their sensory apparatus that people know whatever they know. The view that it is our sensory apparatus that knows (or "knows" if that is different) is something I find incomprehensible. Can you explain what you mean?

I found it difficult to accept myself, so I sympathize.

The thing that finally convinced me was ironically perhaps a computer program rather than a person.

Much of this description will be over simplified, as a full discussion would be too long to post here. I'm also going to forgo references for now, if you express interest after reading this I'll go to the effort to dig them up for you. I hope you'll forgive my laziness.

The problem that our visual system solves is extraordinarily complex. The primary input to the system is the eye of course, but we should set aside most of the eye's complexity for the moment as most of that organ's function involves focusing a clear image on the retina, along with some tracking information. Let us just say that vision begins with a projected image of light that has reflected from the environment.

This image is registered by structures in the eye, that react to the light by stimulating nerves at the back of the eye. The nerve bundle caries this information to the visual cortex where it is transformed into perceptions. Ultimately our conciseness receives several different types of information. We see colors, light and shadow of course. We see objects and entities. We receive information about trajectories, and rates of speed of objects, and creatures. and much more.

The information received in this way, which most intrigues me is the three dimensional "model" of the space we see. You know for instance how to navigate through a room, in part because you can plot a course using this information from your visual perception.

Think for a moment about how complex the process is to reach out and pick up a cup. Think consciously about how your arm must move, how each angle of your joints and the flexing and relaxing of the mussels which set these angles must occur, each at the right time with the right level of exertion.

It is very difficult to move this way intentionally, you will likely catch yourself cheating. The point is not only to illustrate the complication of the task, but also to show the effortlessness which which you do even more complex tasks all the time. Your brain is doing a tremendous number of very clever things behind your back

In order for your brain to accurately plan this motion it requires a model of the environment, as well as a model of itself (your sense of body awareness.) The question is how do we get such a model?

Consider the form of data your vision collects for a moment. The image projected on the retina contains what is essentially a pattern of colored splotches. It is not exactly an image in the usual sense because of peculiarities of the eye's function, but for out purpose here let us pretend it is like an image on the computer. That is, let us assume that your eye receives a pixelated image that it passes along to the brain.

From this image your brain must construct a model of reality that could have produced it. I don't want to get into issues of edge finding algorithms so you'll have to take my word for it that it is possible to calculate where lines and regions are in the image. This it turns out is the easy part (And brain research has detected these sorts of basic processes happening within us.)

Transforming this information into a 3d structure turns out to be harder than we think. One major issue is in deciding what shape in the world corresponds to a particular arangement of lines. There are patterns of lines which are innately ambiguous you may have a set of lines which could be an indent or a bulge for example with equal evidence of both views. Mathematically it is impossible to determine which option is correct.

So how do we do it? Well it turns out that if you make certain assumptions you can get the right answer with high probability. The key is that these assumptions must have a very high level of correspondence with the way the world actually is.

One example is the assumption that a particular scene is evenly lit, this lets you use differences in shading on either side of a line to determine which way the fold goes. Another is that objects are continuous in texture and color, this can increase the accuracy in a similar way. there are many other rules like this.

A computer vision researcher (apologies for not remembering the name) discovered this while working to make a program that could decode images into 3d models. (this is not particularly new research) He faced with exactly the problems we've been discussing here. So he cheated He equipped the system with rules based on valid assumptions about the world and was able to achieve a high level of accuracy. (note that in the research I'm referring here the images were 3d looking shaded line drawings, not photos)

This in itself could be dismissed as irrelevant to how our visual systems structure except for one very interesting discovery. When he fed his program images of optical illusions that we humans perceive as ambiguous, the program saw what we see! The state of it's model alternated between the two possible solutions just as ours perception does.

The key is not that the program was imperfect, but rather that it was imperfect in the same way that we are imperfect! To me this is profound evidence that we work in a similar way.

If so, then our visual apparatus has knowledge of the world in the form of rules about the behavior of light's interaction with mater. This knowledge is of course implicit most likely rather than explicit, and clearly we don't have conscious access to these calculations.

I apologize if this is disorganized, I'm not going to edit it.

It isn't that I don't accept it. I don't understand it. It is people who know things (or don't know things). And maybe computers (although I would doubt it). But how could sensory apparatus know things? We know things using our sensory apparatus, but our sensory apparatus cannot know anything any more than our left big toe can know things.

The system "knows things" in an implicit sense, that is the mechanisms of vision utilize rules which are representations of how light behaves. And that some of these rules do not come from geometry, and are not, and can not be learned from experience. It appears that there is in fact some "innate knowledge" not necessarily in the Greek sense of the term.

If you're just caught up on the word itself, I'm not sure what I can do to help. Consciousness is not required by the definition of knowledge I'm using, maybe that's the point of confusion.

With regard to the brain in the vat argument, there is research going on right now which aims to send camera signals down the optic nerve bundle, to help blind people see. There has been some early success. This argument will likely be resolved, at least for vision in our lifetime.

I am sorry, but I cannot understand how my retina, my optic nerve, and the other anatomical parts which are part of my sensory apparatus for vision knows anything, any more than my hand knows anything. (Except in the metaphorical sense that when I lay my hand on your face I can say "my hand knows who this is". By which, of course, I mean, that by feeling your face I know who you are).

I am afraid that I am "caught up in words" because if the words do not make sense in the context, then I cannot make sense of them.

I do not see what your comment about the BIV argument has to do with it. However, you still have not commented on the theory that underlies the BIV argument, namely that we never observe objects, but only our own private sensations.

I did address the question. You say that we perceive objects in the world, and I proposed a biological objection. What I'm saying is that our perceptual equipment is far more complex than you imply, and that objects do not enter the mind at all in a biological sense.

The "idea of a specific object" that our minds work with is a mental construction formed from a combination of sensory impressions, and a huge amount of data processing that goes on in the brain mostly beyond (below if you prefer) consciousness. The visual cortex in humans is a gigantic organ, compared with other parts of the brain who's function is known.

I interpret you to be saying that we perceive with our minds things which are actually in the world, and I'm saying that while this statement is "effectively true" in certain contexts, it is completely untrue in the details of function, and thus has implications which are untrue as measured against reality.

If we were discussing the form of idea construction I would agree that our minds at many levels (including the conscious) do work with "objects." However I would still disagree as to the origin of these mental constructs.

I'll ask again explicitly, if we directly perceive objects in the world, via what mechanism? How does this mechanism function? Why does the function of this mechanism result in various forms of mental illusion? Why does menthol on the skin feel cold, if not because of a peculiarity in the structure of our temperature sensing organs and an accident of the particular shape of menthol molecules? From where do optical illusions spring, if not from the cracks in our processing strategies for visual data?

These are not trivial questions, they speak directly to how we know the world, and the answers in part determine what kinds of knowledge is accessible to us.

I've offered an example of how certain aspects of our visual system function (shape modeling from edge geometry and shading), and how this leads to specific defects in our understanding of the world (optical illusions.) Actually our ability to perceive pictures as having content is another fluke of our visual system. A picture of a chair is not a chair, but we have no difficulty deriving knowledge from photographs.

I can offer you many other examples:

Photographs often need to be modified in order to fit our expectation of reality. Honest photographs are often need to be white balanced, color corrected, desaturated etc, because without this additional processing the images don't look "proper" to us. The photos are a direct measurement of reality and they look wrong to us!

Mosquitoes exhibit some very interesting behavior in order to avoid being slapped. They exploit defects in our visual system to disappear from view like a ninja, giving them time to move to anew angle out of view from which to approach. One defect they exploit is that the retina responds to changes in activation level rather than presence of activation. In other words, the eye sees only change. Normally we constantly shift our eyes slightly to slide the pattern of light from the world around the retina, and use tracking information from the eye's tactile nerves to align the shifted images. Mosquitoes fly in such a way that they stay still in relation to the shifting of the eye for the fraction of a second necessary for our retinas lose them momentarily.

[As an aside, does this constitute knowledge of our visual system (which is similar in many respects to other mammals) in the mosquitoes? Or is this an automatic behavior on their part?

Your system of thought in this mater would seem to insist on the later, while I would say that the instinctive system "has knowledge of our visual system in an implicit sense." I would also say that I doubt the mosquito is "conscious" of this knowledge.]

What do you think about these things? Specifically how does your theory explain the defects in our sensory apparatus?

My argument has the advantage of copious evidence, perhaps you would provide me with something which corroborates you theory? I'm still trying to guess exactly what your theory of perception entails.

I don't know what "effectively true" means as contrasted with just "true". But the "mechanism" is, of course, exactly what physiologists of perception tell us it is. I hope you don't think I am disputing with the scientists, do you. But it doesn't follow, so far as I can tell, that what the physiologists say implies that we do not perceive objects directly.

The fact that we sometime make mistakes doesn't imply that what we see are not the objects. But it is not clear what you have in mind by optical illusions. It is a fact that when we look at things from different angles or under different conditions, that we have different perception of the same thing. But why should we suppose that if we were perceiving the object, it would not look different under different circumstances, and so that we were not seeing the object?

Yeah I did, because, my interpretation of your words is not compliant with science


Ah yes, but they are not just any mistakes they are consistent, reproducible dysfunction. They are always "seen" and thus are not mistakes in the usual sense. You can learn about mistakes and correct them by changing the way you think! Optical illusions cannot be removed from our experience via learning. You can learn to disregard them as false data, but you will continue to see them.

But let me try another tack. Where does your disagreement lie in the following sequence?

1 Light reflect from an object.
2 Light enters the eye.
3 Light stimulates organs in the retina.
4 Organs in the retina stimulate nerves in the back of the eye.
5 the nerves carry a signal to the visual cortex at the back of the brain.
6 The visual cortex constructs a model of the object.
7 The visual cortex sends this information to other areas of the brain which do their thing.
8 We experiance seeing the object.
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Here is a page all about what I mean by Optical illusions: Optical Illusions and Visual Phenomena

I was just looking at this site and I thought this was funny:

If we are brains in a vat, it matters very little to our existence. Because we are stimulated by sense data of the external we experience (whether that real world is real or illusion does not matter), and not sense data from vats, it would have little effect on us if we came to the conclusion that we were brains in vats. Now if we were BIVs and had vat thoughts then it may matter to us.

I could take the question one level higher:

How real is reality itself? How can we tell it is not just a show staged for some unknown reason with us as actors who don't even know they are playing a role.
For all we know, the entire physical universe can be fake. That would imply even our brains themselves exist in some kind of vat and are really thinking 'vat' thoughts.

I wonder what would make anyone think we are BIV. Especially all of us. Who would have created the vats?
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Theaetetus strikes at how I often argue with (against?) skepticism of this nature:
The question seems to be unanswerable: as much as many of us would like to assert the reality of reality there is little recourse to prove that the basis of this world is its existence rather than a program of a computer. However, the reality I experience is no different whether ontologically is is reality itself or a computer program. There can be no assurance one way or the other as to the reality of reality, which means that there should be no difference between a reality-reality or a computer-reality in my general being-in-the-world. If such a difference was evident we could use it one way or the other to show what this world is, but in its absence either hypothesis remains possible.

In this vein we have a problem we cannot possibly solve that has no actual effect on how things operate. We can't experience a difference between reality and a computer-reality, so is there a reason to be concerned as to whether or not we are in one or the other?

kennethamy points to another skeptical hypothesis: do we know if the world was created five minutes ago? My answer would simply be: does it matter (in either case)?

Excelent points Blue Chicken. Of course it doesn't matter, and that is the important realization.

Also I saw this recently and think it's appropriate: xkcd - A Webcomic - A Bunch of Rocks

... ahhhhhhhh - now you're bringing Occam's Razor to bear ... so is there anything worth saying regarding which scenario is the most likely? - or is relative likelihood yet another problem to which there can be no "proof"? ...

Nothing about my experience in the world makes me think I am a brain in a vat, but nothing about my experience in the world can prove that I am not a brain in a vat.

As far as I can see, you can't falsify the BIV concept. That doesn't make it particularly meaningful to our lives.

I accept the epistemological skepticism entailed in this concept, but I don't live every second of my life worrying about whether I can really know anything or not. The point of skepticism is interesting, but the effect it generally has on life doesn't seem to be as much so.

Not only could it be true, it IS true.
What are our bodies, other than highly scientific supercomputers sending electronic impulses to our brains?

I think the thought experiment relates well to the concept I am struggling with concerning the relationship between knowing and trusting. I recall a professor using the example of the physiological process of vision (that was so well related by Quatl) to make the point that indeed we don't experience the world directly. This professor was not trying to drive us students toward some extreme form of skepticism, but, rather toward what he called "critical realism." The basic idea was just that, as we interpret our day to day practical lives, there's no need to be (and indeed it would be disfunctional if we were to be) so analytical about the vast majority of things we take for granted as knowledge. The world is "real." We see things, and we know they are there, and we don't bump into them. However, when we experience more complex or deceptive visual phenomena it's good to recognize we are susceptible to all kinds of illusions. One good result: it helps us to not become so naively confident about what we "know."

Are we BIV, I would guess not. Could we be, yes. Does it matter to me, not at all. That business finished, I'd like to ask everyone what they mean by reality? There's alot of talk about the 'reality of reality' that begs analysis.

Having read through this entire thread, I would like to summarise my views:

1. Regarding the discussion on visual perception (up to post #28), I think kennethamy is right that we perceive objects in the world, but Quatl is right that we do not perceive them directly. The objects themselves create sensations, or sense-data, in our visual reception apparatus, which are then reconstituted as object-perceptions by our brains. The object-perceptions usually correspond closely to the objects themselves, but in some conditions they do so less closely, and in some optical illusions they do not correspond to real objects at all. Normally, we really do perceive the objects that are 'out there', but the process is an indirect one. I wonder if kennethamy and Quatl would both agree with this summary.

2. We could be brains in a vat, but Occam's Razor makes it slightly more probable that we are not. But ultimately it doesn't matter.

3. As to 'reality':
(a) At least something must be real; it would make no sense to call everything unreal, since unreality implies some contrasting reality.
(b) My own experiences, in themselves, are real. I know I really exist, and I cannot be mistaken about my own feelings. If I think I am in pain, then I really am. When I think I perceive an object, I really do perceive something - either a real object or a real illusion.

I agree ACB. That's what was bothering me, I notice people (not neccessarily right here in this thread, but in general) who like to claim that things are not real when it really makes no sense. Something does indeed have to be real for something not to be real. While something must be real, does something have to be unreal? Does it even make sense for some-thing to be unreal? I guess it depends on the context.