CHAPTER ONE: How Seeing Works

“These lovely lamps, these windows of the soul.”   
Guillaume de Salluste

Overview

Before trying to understand images themselves, we should develop a basic idea of how the eye and the brain work together to allow us to see the world and the things in it. In a sense, our vision is rather narrow - we only see a small sliver of the natural world at any one time – and for this reason, the brain is constantly working hard to weave these slivers into a comprehensive visual understanding.

The Vision Thing

Seeing is astounding when you think about it.

The notion that the universe, in all its teeming multi-dimensional complexity, can somehow be grasped by some tiny cells and lumpy gray matter in the skull is amazing enough.  That this is possible because a narrow range of energy in the form of reflected light gets squeezed through two tiny pinholes in the front of the head is nothing short of miraculous.  And of course that same grey matter can create visions in the sense of pictures in the head, imagined futures, even convincing delusions.

Vision is a primary way that we make sense of and come to understand what there is.  It is not the only way of course; people without sight understand the world too.  But for those with vision, seeing is one of the most fundamental ways of knowing.  For most of us, using our eyes is what we do and the vision thing is the way we live.

The Eye/Brain System

As a practical matter, we should not talk about seeing by thinking only about eyeballs, as complex as they are.   We see with our brains as well as our eyes.  Or to put it another way, we see with our eye/brain system.  Without the brain, the eyes would be cold cameras. The eye is a fascinating organ but it is the brain that makes what the eye sees meaningful.  Without the eyes, the brain cannot see.  Only together do they form and inform our vision.

Because this is the case, using the eyes is always using the brain and seeing is always thinking.  PET scans of the brains of people looking at things show this to be the case.  The visual cortex, the area in the back of the brain that handles vision, explodes with activity whenever we look at something.  This firestorm of impulses goes on as long as our eyes are open.  It happens when we dream too, by the way, or even visualize something in our mind’s eye because vision, even inner sight, always involves the eye/brain system.

Those PET scans also suggest that seeing is never a passive act.  Seeing is active all the time.  Seeing is a thinking process, a brain process…creative and constructive.  The brain is always working at it, taking tidbits of visual information and weaving it into a big picture in the mind, struggling to make sense of what we see and to fit it into the mental image of life that we have.


The Feeling of Seeing

You are seeing right now of course, as you read this.  Hopefully you are so interested in what you are reading so that you are not aware of guiding your eyes across the words of the page.  If you take a break from the text and look away for a moment, you will be seeing something else.  And as you continue through the day, you see an endlessly shifting pattern of light.

Studies of babies show that early seeing involves a massive attempt to make sense of this swirl of color as the brain begins to assemble a catalog of shapes, objects, motion, etc.  We are experts at this process so that once we master it, seeing does not feel like much of an effort.  We are barely aware of any qualia connected with seeing.  The word qualia refers the way something feels and if you stop to consider how it “feels” to see, you generally come up blank.  Seeing just does not feel like anything.  We have no sense – no awareness while it is happening – of the activity of the eyes, the processing of the light, the explosion of impulses through the visual cortex at the back of the brain.  And no awareness of the mind struggling to absorb, categorize, assess, analyze, file and store what we see in every moment.

That is why, unless something unusual happens, we are usually not aware of ourselves seeing and looking and watching.  They feel like nothing much at all going on.  But that is an illusion.  In reality, it is a firestorm in the brain because whole looking at anything – even mindlessly watching paint dry – the visual cortex is exploding with signals.


The Visual Tapestry

Why is this the case?  What is going on back there in the brain that is so important?  What is the brain doing when it is doing all this activity? Exactly what happens when we look at something?

One answer is that the brain is trying to build a model of the world out of very few blocks.  The problem is not that vision is so vast but the opposite.  Although there is a great deal of data to take in and organize, the scope of vision is rather limited because the eyes can only take in a thin sliver of the world at any one time.  Because of this, the brain has to work hard to use this limited information in more complete ways.  The visual cortex works constantly to sew minute amounts of information together into a tapestry of what we see.  That is the reason for the frenzy of brain activity when you use your eyes, even though it does not feel like much is happening at all.

Historically, there have been many theories about how the eye or the brain or both together accomplish this.  The Greeks thought that the brain sent out light through the eyes to illuminate the world; during the Middle Ages it was thought that a little man inside the brain called a homunculus, studied what the eye took in and made sense of it.  By the time of the Renaissance, when people began actually opening up the brain and looking at it, it was clear that what you find inside are no mechanisms or men, just brain mash.  And it was not until the 20th century that studies of the mash itself revealed the hidden structures of neurons that make up the brain and the cells at the back of the eye that translate light into electrical impulses.


Structures of Vision

In the first place, the eye itself is an orb, a roughly spherical organ.  This shape allows muscles that surround the eye to move it in its socket easily.  This is important because it allows the brain to direct the movements of the eye independently from movements of the head, giving greater control over seeing.

The eye is one of only six organs in the body that allows information from the world to come directly into it.   The ear, nose, mouth, tongue, and skin are the others.  The eye does this through a small hole in the front called the iris.  It is through this tiny hole that light rays from the world enter the body and begin the process of visual perception.  It is amazing to realize that the entire visual experience of life has all come in through these two tiny holes.

Just behind the iris is the lens.  The word lens comes from a Latin word that means lentil, and in fact the lens is shaped like a bean.  It is this shape that allows the lens to focus rays of light from outside onto a tiny area at the back of the eye where they can begin to be processed by the brain.  The lens too has muscles than can alter its shape and therefore alter how the lights rays are focused.  These muscles allow us to focus our vision, to both see objects in the distance and also read fine print with the same lens.

To prevent dust and other debris in the air from damaging the lens, the eyeball is covered with a thin film of mucus that is constantly wiped clean by the blinking of the eyelid.  The size of the iris can be changed by another set of muscles called the cornea.  This allows more or less light to enter through the iris, which gives us the ability to see in both bright sun and dim light.  This is equivalent to the aperture of the camera.

The inside of the eyeball is filled with a fluid.  If you have ever seen floaters while looking at a white surface, little transparent assemblies of cells, these are actually hardened bits of the fluid that float inside the eyeball, not on the surface of it.

Perhaps the most extraordinary part of the eye is a postage-stamp sized group of cells on the back of the eye, directly opposite from the iris.  This is the retina and it is the most delicate and complex part of the eye.  The retina is basically an array of photosensitive cells and in this way is very much like the chip inside a digital camera.  It is a flat surface (but curved because it is part of the rear of the eyeball) packed with two types of light sensitive cells, about 130 million of them.  Cones, so called because of their shape, are sensitive to colors.  Rods are more sensitive to changes in tonality or light and dark and help us to see in dim light.  The third kind, called bipolar cells, transmit signals to the optic nerve.  The bipolar cells are connected to neural cells that gather together and pass through a hole in the back of the eyeball (like a video cable), then to other cells in the brain and eventually to the visual cortex at the back of the head.

The eye/brain system is a lot like a digital camera in that both convert photons of light into electrical signals.  But that is where the similarity ends because the eye is connected to the brain and the brain makes visual sense of what is seen.  Exactly how exactly the brain with its100 billion neurons accomplished this is still a mystery.


Slivers of the World

If you close your eyes, you can easily visualize the world around you…in great detail and depth if you need to.  What you know of the visual world is based in large part on what you have seen of it. This includes your own direct personal experiences (what your room looks like, for example), images you have seen (pictures of Saturn, for example) and other visual representations (a chart in a newspaper that shows crime on the increase, for instance.)

Of course there is infinitely more to the universe that you have not seen at all. As incredible as the eye is, it is quite limited in its ability to take in the world. In fact, we only see a tiny little slice of the universe through our eyes.  We can only detect a tiny range of energy we call visible light and only within certain boundaries of time, motion, brightness, etc.  

As suggested earlier, this means that the brain has to constantly work to convert this limited information into a useable visual model of the world. And that model is seamless, complete, full.  You do not tend to think of the world around as having gaps or holes or missing parts.  On the contrary, you think of the visual world that you know through your experience as being all there is to see.

Seeing in this sense is therefore not just active…it is constructive.  We build the visual model from bits and pieces; we create the visual world as we look at it.


Brainwork

We are so adept at all this that we do not notice the effort and in fact take all the brainwork that goes into it for granted.  The reading connected to this chapter demonstrates this vividly.

In a fascinating section of the book Seeing, writer Annie Dillard focuses on experiments that allow patients who have been blind from birth to suddenly be able to see.  These studies show just how much work is involved in every visual act, all the tiny calculations the brain makes to makes sense of what we see, all the things we must learn in order to see.

The experiments demonstrate how the perception of depth, size, distance, color, shape, space are things that have to be learned, sometimes with great anxiety and frustration.  One patient, for example, cannot conceive of the idea that the house might be bigger than the room he is in because this is a visual understanding.  Another cannot distinguish objects but sees everything as a confusion of colors.  One woman thinks that shadows are objects themselves and complains that the world looks flat with dark patches.  Another thinks that an object blocked by a closer one is not just hidden from view but is simply no longer there. A surprising number of these individuals would prefer to return to their familiar unsighted environment.

A video about Michael May, whose sight was restored after 43 years, shows just how complex the brain activity involved with ordinary seeing can be. These kinds of examples remind us that vision is a complex task of the eye/brain system – one we very easily take for granted – that is rehearsed endlessly as we go about the world with open eyes.

Image Assignment

Find an image from any source and on any subject that you think is fascinating, intriguing, captivating, mind-blowing, or startling (or to which you have any other strong positive reaction).

Write a paragraph explaining what it is about this particular image that makes you feel this way about it or have this response to it.  What do you see in the image that attracts you to it?

This assignment is due by the next class. Remember to put your name, the words Assignment #1, and where you found the image at the top of the paper.

Extra Credit

Find an image from any source and on any subject that you think is fascinating, intriguing, captivating, mind-blowing, or startling (or to which you have any other strong positive reaction).

Write a whole page to explain what it is about this particular image that makes you feel this way about it. 

Write about whatever you think is important about the image that has an impact on you, but here are some ideas that may help you think about its effect:

Is it the subject matter (what the image shows) and if so, what about it?
Is it the look and feel of the image (the appearance of it) and if so, what aspects of it?
Is it something else about what the image is communicating to you (personal, emotional, visual?) and if that is the case, what is it exactly?