Did you ever notice? There is something ver-ry strange about this world of ours.
Really? Like what?
Do you ever feel like you are trapped in some kind of bubble? I mean look—the sky looks like a dome over my head. Is that really the shape of the sky? And did you notice something really funny?
No what? Tell me!
Did you ever notice that things that are far away look smaller? And things that are nearby look bigger! Do you realize how strange that is?
Strange? That’s not strange at all! Thats just perspective, just like it happens in a camera. In a photograph farther things look smaller, too.
Yes, but the perspective in a camera is projected onto the flat sheet of film. There is no mystery in that kind of perspective, it is simply a projection from a 3-D world through a focal point onto a 2-D surface. And in your eyeball the retina is like the film.
But take a look at this street here. Is this street the picture on your retina?
No, that’s the street itself where the light comes from that makes the image on my retina.
But then how come things in the distance look smaller? Perspective is something that happens in your eye, not out in the world! In the real street things in the distance are not actually smaller, all the houses are exactly the same size. It is only on your retina that the farther ones appear smaller. And the image on your retina is only a flat 2-D image. This world out here is 3-D, but it has perspective. So is it the world itself? Or is it the image on the retina?
Well, it’s both. Light from the world makes a picture in your eye that lets you see the things out in the world. What’s so hard about that?
Ok then if this is the world itself, then why is everything bent around like a reflection in a Christmas bulb?
I don’t see anything bent. What are you talking about?
Well, take a look at this. See the two sides of this street? They are straight and parallel as far as the eye can see.
But LOOK! Those straight parallel sides also MEET AT A POINT! RIGHT THERE! Can you SEE it?
Well they LOOK like they meet at a point. But they don’t really!
And if you turn around and look behind you, they meet at a point back there too!
So? I don’t get it.
So this street that we are standing on is shaped like the rind of a melon slice with two curved sides that meet at a point at either end. And those end points are at eye level, even though the street is under our feet.
Ok, vision is not perfect. So what?
So what? So we are living in a scale model, and the scale of the model shrinks progressively with depth, just like a museum diorama, or a theatre set. And at the back plane the scale shrinks to zero, at least in the depth dimension, where everything beyond a certain distance appears flat, as if painted on the dome of the sky.
But it only looks that way. It’s an illusion. We know that the world isn’t really warped like that.
Yes but HOW do we “know”? We “know” by using a warped reference scale to judge the objective size of things in the warped subjective world. If we measure distances, and even straightness itself, using this warped reference grid, we can see that all the houses are the same height and width and depth, and that they are really all straight and vertical, not warped and bulgy as they appear.
I don’t know if I see anything warped at all! Looks perfectly straight to me!
Of course! Relative to your warped reference scale! And take a look at what happens when you walk down the road. Things from far away expand outwards and get bigger and bigger until you pass them, and then they shrink back down again to a tiny little dot before they disappear altogether!
Hmmm, I suppose it is a bit like some kind of bubble.
And the strange thing is that the part where the world is biggest, is always right where you are standing. Now look- you stay here and let me take a few paces. See? now my world is the biggest here where I stand, but your world is biggest over there where you stand. Either the world is a very elastic place, or you and I are looking at different bubbles.
But how can that be? Wouldn’t our bubbles collide?
Either that or they’re all part of one big elastic bubble. Except you’d think that I could see the distortion of your bubble from mine, and vice-versa.
No, that can’t be right either.
Well then the only other possibility is that we each have our own private bubble, and we can never see into anyone else’s bubble.
But how can that be? You can see quite clearly that we are both standing right here in the same space.
It only seems that way because in my bubble I have a picture of me here and you there, while in your bubble you have a picture of you there and me here. The pictures in our two bubbles are so similar that we assume that we are in the same space.
But then where are these bubbles? What are they made of? And whatever happened to the real world that we know exists independent of our experience of it? Where did it go? Does it not even exist? Is everything just a hallucination or lucid dream?
Of course it exists! Otherwise there would be nothing to keep the picture in your bubble synchronized with the picture in mine. Can’t you see? We are both looking at this same house from different perspectives, so there must be a real house there to be the common cause of both perspectives. We are each seeing our own virtual-reality replica of the real world, each from our own unique perspective.
But where is this virtual-reality picture? What is it made of?
If we know anything about neurophysiology, we know that it must be in the brain. The brain is the organ of conscious experience. Mind is nothing more than the operation of the physical brain.
So you’re telling me that everything I see around me is actually inside my head? How can that be? My head is right here, and all that is out there!
You cannot see the external world directly. You can only see it through your private conscious experience of it. So this world you see around you is the picture in your brain. In other words beyond the dome of the sky above, and beyond the solid earth underfoot, is the inner surface of your true physical skull.
Impossible! I don’t buy it! I don’t care what you say, I know this is the world, not just a picture in my head! I don’t see any curvature, the world is just plain straight. You must be crazy!
Ok, then you tell me. How does vision work?
Well, first of all, this here is the real world, not some kind of image in anybody’s head. And there is nothing bent or bulgy about it, the world is perfectly straight! The sides of the road don’t converge, they only seem to converge. And they never do actually meet, if you look very carefully. And farther things are not really smaller, they only appear to be smaller. It’s an illusion.
Now light from the world enters your eye where it makes an image on your retina. The retina sends an electrical signal up the optic nerve that generates electrical activation in the visual cortex.
And as the cortex lights up electrically, you see the world around you.
Is the electrical activity in the cortex shaped like a street with houses under a domed sky?
No! Neurons chatter away in the brain in a pattern that is nothing like the shape of the world you see.
Then where does the shape of visual experience come from? Where is the picture that we see?
The world! It comes from the world! The shapes and colors you see around you are shapes and colors of the world, not patterns in your brain!
But what if you are having a lucid dream, or a hallucination? Then you are seeing shapes and colors that are not in the world. Where are the shapes and colors of the hallucinated scene?
They’re in your head of course! But in your head they do not have the shapes and colors you see. In your brain they are just a bunch of neurons chattering to each other.
But then where do the shapes and colors you see come from? Why don’t you just see the shapes of the neurons and their activations? What is it that turns the patterns of electrical activity into the patterns that we experience?
The pattern of electrical activation in your brain during a hallucination takes the same shape as it would during a normal perception of the hallucinated scene. So the shape and color that you experience are the shape and color that the world would have if you were perceiving it instead of hallucinating it. They are the shape and color of the world, not of your brain! Even if that world is imaginary!
But then what determines which neurons, or patterns of activity, represent which experienced shapes? What is the mapping between the shape of the neurons, or patterns of activation, and the shapes that we experience?
The mapping is learned from experience! One neuron, or neuron assembly, learns to fire whenever you see a house, while other neurons, or assemblies, learn to respond to windows, doors, and roofs, for example. The collective pattern of activation of all of these neurons together corresponds to our experience of the external scene.
And in dreams and hallucinations, the same constellation of neural activations produces the same kind of visual experience as a perception of the corresponding real scene!
But where is this experience located? We can see quite plainly that it is a spatial structure. But where is that structure? What is it made of and where is it located?
It’s out in the WORLD of course! Experience is right out here in the world where we observe the world to be!
So, let me get this straight. Experience is a spatial structure, as we can plainly see. And your experience occurs as the result of some kind of activation in your brain. But your experience is not in the brain, it is out in the world, although it is caused by electrical events in your physical brain.
Yeah, thats right!
So let’s say I had a switch that could turn your brain on and off like a light bulb. Are you telling me that every time I turned it on, the experience would appear out there, but when I turn it off, then the experience disappears? Is experience like a beam of light from a flashlight that is projected outward from the brain? What is that experience made of? What is its substance?
Its not made of ANYTHING! It is just EXPERIENCE! It doesn’t really EXIST in a physical sense! Nothing is actually projected, it is only EXPERIENCED to be projected!
Doesn’t exist? This here? The fabric of experience? Doesn’t exist??? All this here is really a bunch of scrambled neurons firing in my brain? I don’t care what you say, I see a spatial structure in experience, and if I see it, I know that it exists!
Ok then, how do YOU explain visual processing? How does vision work in the brain?
Well, first and foremost, it is plainly evident that visual experience is a spatial structure, and it is produced by the brain. So unless we find compelling evidence to the contrary, that structure must be located in the brain! How the brain constructs spatial pictures remains a deep dark mystery. But that it does so is an observational fact.
So whether it is by coherent oscillations, standing waves, or some kind of Fourier code, somehow the tissue of the brain must be capable of generating three-dimensional moving images as rich and complex as this image of me that you see here!
Now of course the volumetric image may be warped and distorted in the brain…
…while still being a volumetric representation.
But as long as its connectivity, or functional architecture, is similarly warped and distorted, the warped image encodes the same volumetric information as its undistorted counterpart.
And apparently the volumetric image can even be fragmented into separate modules specialized for processing color, motion, binocular disparity, etc., while still producing a coherent, unified experience.
But whatever else we know about the visual representation, one thing is plainly obvious by inspection: the representational strategy used in the brain is an analogical one. In other words objects and surfaces are represented in perception not by an abstract symbolic code, nor by the activation of individual cells, or cell assemblies. Instead, objects are represented in the brain by constructing full spatial effigies of them that appear to us for all the world like the objects themselves.
Vision is televisual. It lets us see the remote external world through the medium of an internal replica of it.
But who is the viewer of this internal theatre of the mind? For whose benefit is this internal performance produced? Is it the little man at the center who sees this scene? But then how does HE see? Is there yet another smaller man inside that little man’s head, and so on to an infinite regress of observers within observers?
No, of course not! It only goes in one level! Take a look! What do you see inside your phenomenal head? I see nothing! It is an empty void! There is no infinite series of heads within heads, there is just a fuzzy brown emptiness with nothing inside, that opens to the world through the eyes like two open windows.
No, the little man at the center of our world of experience is not the observer of the internal scene. It is merely an object, made of the same substance as is the rest of the perceived scene, because that scene would be incomplete without a replica of our own body in the world. But the perceptual homunculus is more than a mere replica of the physical body. It is a computational mechanism constructed by the brain to help it control the body.
If the representational principle behind visual perception involves an explicit volumetric spatial model of external reality, then sensorimotor function might also be best implemented in the form of an explicit volumetric model of the body, like a wooden marionette, with hinges and ball joints at elbows and shoulders just like the real body that it represents by analogy.
But what makes the internal marionette a meaningful model of the larger body that it represents, is that it is coupled to the larger body somehow, so that the posture of the model always exactly mirrors the posture of the real body that it represents.
(Follow alternate argument path)
Motor control is tele-motive, like a virtual-reality body glove, electronically coupled to a remote android body that automatically replicates its posture.
Except in perception that android body is not remote, but surrounding, like a body glove suspended in a control room which is located inside the head of the giant android body that it controls.
And projected into that control room is a volumetric colored replica of the surrounding environment constructed on the basis of sensory input.
As the controller cavorts about in this synthetic reality, the larger android body cavorts in the external world, giving the controller the impression that he is interacting with the external world directly…
…although there are also times when it becomes abundantly clear that our view of the world is not direct or unmediated.
Now despite appearances to the contrary, the little man at the center of our world of experience is not the viewer or ‘experiencer’ of the surrounding virtual world. The body-image homunculus is just the interface between perceptual and motor function, expressed as an explicit model of the body in an explicit model of surrounding space.
Motor computation takes the form of spatial field-like forces in that space, that bend the body-image homunculus into different postures…
…and those postures are then mirrored in amplified form by the larger android body.
But the coupling works both ways. Forces from the external world are also communicated back in to the model world. For example gravity drags the android body downwards against the ground that pushes upward…
…and these forces are also replicated in the model environment where we perceive them as actual forces in what we believe to be the external world. The perceived force of synthetic gravity makes sense of the persistent resistance felt to upward motion of the body, just as the resistance of the ground underfoot to penetration is perceived as an upward force of rigid support.
We resist forces like the pull of gravity by constructing an equal and opposite force of levity, that raises our body-image homunculus upward against the downward pull while pushing downward against the ground. This symmetrically opposed motor force field is a spatial thought that appears under voluntary control, and it acts on the body image as a motor command. And as the motor force field moves the body-image homunculus…
…the larger android body moves in perfect synchrony with it, pushing harder against the ground to raise itself upward against gravity.
We move our hand by simply willing it to move in any direction we choose, and that will is itself a force that acts on our body-image hand which moves in response to the willed force. The larger android hand moves in synchrony, as if it were itself under the influence of a larger external force pulling it in the willed direction.
And our desire to move through the world is expressed as a larger force field that pulls on the entire body-image homunculus. But since the homunculus is anchored to the center of the control room, the only way he can advance forward…
…is by pushing the world backwards until his destination comes to where he is, or so it seems perceptually, resulting in real progress of the physical body through the physical world.
Perceived objects in the perceived environment also exert attractive and aversive forces that influence the movement of our body through the world. So whenever we perceive an object to be attractive, it automatically exudes an attractive field that tends to pull our body image towards it in perceptual space.
The larger body moves through external space exactly as if it were responding directly to field forces from the external world, except that these forces actually exist only in the internal perceptual world.
(Follow alternate argument path backwards)
And when we perceive something to be aversive, it automatically exudes a repulsive field that pushes our body away from it in perceptual space.
The subjective impression of being attracted or repelled by attractive and repulsive stimuli is not only metaphorically true, but this subjective impression is a veridical manifestation of the mental mechanism that drives our motor response.
So in a sense it is the sensorimotor homunculus for whom the internal world of perception is constructed. But that homunculus does not “see” the internal scene…
…but rather the attractive and aversive features recognized in the scene exert forces on the body image homunculus, which in turn result in body motion through the environment.
Once we recognize the world of experience for the internal representation that it is, the computational strategy used in motor control becomes clearly evident by inspection.
So you are saying that vision, proprioception, somatosensory, and motor function are all part of a single integrated analog control system? But brain scientists have discovered a fragmented architecture in the cortex with separate areas specialized for processing visual, auditory, and motor information. How would the activations in all those separate cortical areas integrate to produce a single unified experience? What is the binding force that binds them all together?
They are bound together by bi-directional causal connections, just like the dual controls of an airplane. If the student pulls the stick back while the instructor is pushing it forward, both control sticks move in perfect synchrony because they are connected, exactly as if the two pilots were actually pulling and pushing on the same stick.
In the same way, the different sensory/motor marionettes in different cortical areas are all coupled to each other, as well as to the larger external body, so that forces applied to one marionette are automatically and immediately transmitted in parallel to all the rest.
And if different forces are applied to different marionettes, the resultant body motion is exactly as if all of those forces were acting on a single virtual marionette.
So visual data is expressed in the visual representation, body posture is represented in the proprioceptive representation, and motor planning is computed in a global motor planning space. But all are coupled to form a single visual/proprioceptive/motor space, which is the space that we experience.
Each of these diverse representations are expressed in their own specialized slab of cortical tissue, although these areas are tightly coupled so as to form a single integrated computational module.
That is the most incredible hypothesis I have ever heard! Tell me honestly now—do you really believe this? Or are you being deliberately provocative for the sake of argument?
Look—if you once just accept the fact that this world we see around us is a picture in our head, all the rest of it follows by inspection! Besides, the alternative view, that we can somehow see the world directly, bypassing the sensory machinery in the eye and brain, is just plain magic!
So it comes down to a choice between two incredible hypotheses. Either you believe the incredible notion that your skull is larger than the entire perceived universe…
…or you believe the absurd notion that we can experience things outside of ourselves directly, beyond the sensory surface! One of these two incredible hypotheses simply must be true, and the other is just plain wrong!
Which one do YOU find less incredible?
Send comments and opinions to: Steve Lehar (slehar _+_a t _+_ g m a i l + c o m). Interesting comments or logical objections will be posted HERE.
For an in-depth philosophical presentation of the epistemological debate, see my on-line paper:
Gestalt Isomorphism and the Primacy of the Subjective Conscious Experience
or read my book
The World In Your Head: A Gestalt view of the mechanism of conscious experience